• Analysis and data processing
• Vector
• Geoprocessing tools
• Introduction
• Accessing the geoprocesses
• Buffer
• Introduction
• Creating an area of influence or buffer
• Lateral buffer
• Intersection
• Introduction
• Running the 'Intersection' geoprocess
• Clipping
• Introduction
• Running the 'Clipping' geoprocess
• Dissolve
• Dissolve
• Running the 'Dissolve' geoprocess
• Split lines
• Merge
• Introduction
• Running the 'Merge' geoprocess
• Convex hull
• Introduction
• Creating a convex hull
• Difference
• The 'Difference'
• Running the 'Difference' geoprocess
• Union
• Introduction
• Running the 'Union' geoprocess
• Spatial join
• Introduction
• Running a 'Spatial Join'
• 2D Translation
• Introduction
• Translating a vector layer
• Reprojection
• Introduction
• Reprojection of a layer
• Exporting layers
• Introduction
• Exporting a shape
• Exporting to dxf
• Exporting to postgis and Oracle Spatial
• Exporting to gml
• Exporting to kml
• Annotation layer
• Introduction
• Creating an annotation layer
• Editing an annotation layer
• Annotation layer properties
• Adding an annotation layer to the view
• Example of how to create an annotation layer
• Export to a raster layer
• Creating a layer with derived geometries
• Raster
• Layer functionalities
• Filters
• Description
• Enhancements
• Spatial filters
• Colour adjustment
• Edge detection
• Masks
• Histogram
• Description
• Preferences
• Radiometric enhancement
• Save View as image
• Clipping layers
• Zoom to raster resolution
• Automatic vectorization
• Analysis view
• Geographic Transformations
• Geolocation
• Georeferencing
• Description
• Modifying georeferencing upon loading
• Image reprojection
• Alphanumeric
• Exporting to dbf and xls
• Joining tables
• Join
• Statistics

Analysis and data processing

Vector

Geoprocessing tools

Introduction

The gvSIG geoprocessing extension allows you to apply a series of standard processes to the vector information layers loaded in the layer tree in a gvSIG view (ToC), thus creating new vector information layers which will provide new information for the source layers.

The following geoprocesses have been implemented in the first version of the geoprocessing extension:

• Buffer.
• Clip.
• Dissolve (by adjacents and alphanumerical criteria).
• Merge
• Intersection.
• Join.
• Spatial Join.
• Convex Hull (minimum convex polygon).
• Difference.

The output layer can take one of the output formats supported by gvSIG (it can only be saved in shp format at the moment).

When some geoprocessing tools are applied (for example, Clip) a window appears in which a spatial index can be created for the input layer. This is an internal process which is only carried out once per layer and per new project and speeds up the spatial intersection processes.

To create a spatial index for the input layer which can be used by the geoprocesses, click on “Yes”.

Accessing the geoprocesses

You can run the geoprocesses available in gvSIG with the geoprocessing wizard by clicking on the following tool bar button:

The “Geoprocess toolbox” will appear and you can use it to select the geoprocess you require. To access the different geoprocesses, pull down the tree in the window shown below (double click with the left button of the mouse on the "Geoprocesses" folder and the rest of the folders will appear).

When you have found the geoprocess you wish to use, click on the “Open geoprocess” button.

Buffer

Introduction

This geoprocess generates “areas of influence” around the vector element geometries (points, lines and polygons) of an “input layer”, thus creating a new polygon vector layer.

Several equidistant concentric radial rings can be generated around the input geometries. Moreover, in the case of polygon input geometries, the area of influence can be outside the polygon, inside the polygon or both inside and outside it. Some examples of the creation of areas of influence include:

• Which urban areas lack schools in a 1000m radius.
• Which wells do not comply with regulations on observing the minimum distance between two consecutive wells.
• River bed flood zones to monitor flood risks.

Creating an area of influence or buffer

When you click on the “Geoprocessing wizard” button, the following dialogue appears:

If you select “Buffer” and click on the “Open geoprocess” button, the window associated with this process is shown:

The form is divided into the following parts:

Selecting the elements whose buffer is to be computed. This is a pull-down list in which you can select the vector layer the calculation is to be applied to. If you wish, you can enable the “Use selected features only” check box so that the process only computes the buffer of the elements currently selected in the specified layer.

Inputting the features of the buffer to be computed. You can choose to input the buffer defined by distance (in the first text box) or to input a field in the input layer, from which the buffer radius value to be applied will be taken. This second option allows you to apply different buffer radii to different vector elements (whilst the first option applies the same radius to all the elements in the input layer). When the buffer of all the input layer elements has been generated, the “Dissolve features” option allows you to merge the elements whose geometries touch each other in a second iteration.

The “Rectangle end cap" option allows you to generate buffers with perpendicular edges (not rounded). Selecting the number of concentric buffers and their situation regarding the original geometry. The gvSIG “Buffer” geoprocess allows you to generate several equidistant areas of influence of the original geometry (for example, if the buffer distance to be applied is 200m and you choose to generate two concentric radial rings, the buffer distance of the second ring will be between 200-400m. Currently, you can only generate a maximum of three concentric radial buffer rings for efficiency reasons. If the vector layer we are working on is a polygon layer, the “Create Buffer…” option will be enabled, thus allowing the user to generate buffers outside, inside and both inside and outside the original polygon.

Introducing the result layer characteristics. Currently, the result of running a geoprocess can only be saved as an shp file. Thus, gvSIG allows you to select an existing shp file to overwrite it or to specify a new one. As new formats are supported to save the result of the geoprocesses, wizards will be provided to indicate the characteristics of these formats.

When you have input all the necessary information to compute the buffer, and clicked on the “Ok” button, a check routine is carried out to ensure that the information input is correct: whether the radius distance is numerical, whether the attribute from which the buffer radii are taken are numerical, whether a result file has been input, etc. If the check routine is not correct, a dialogue box appears so that the input data can be corrected.

If the input information that you have entered is correct, a window with a progress bar appears, in which the buffer processing rate is shown.

The process can be cancelled at any time by clicking on the “Cancel” button. As a consequence, the result file and any other intermediate product generated as a result of running the process are deleted. Whilst the buffer computing process is underway, other tasks can be carried out, such as changing the zoom or adding new layers to the layer tree in the gvSIG view. Other tasks can be carried out because all the geoprocessing extension geoprocesses are run in the background. When the process has finished, the new result layer is added to the layer tree in the active view. It is made up of buffer polygons with a specified radius based on the source layer.

Finally, the “Dissolve elements” option can be useful in specific situations (such as when the aim of computing the buffer polygons is to determine the total surface area affected by a phenomenon: quarantine areas, etc.), because when the generated polygons are merged the surface area covered by the buffer will be a real surface area, i.e. the sum of two buffers will not have any overlays.

The above image shows non-merged overlay polygons. The total area covered by the phenomenon does not coincide with the sum of the individual areas.

However, this second image shows merged overlay polygons. The total area covered by the phenomenon is real. When the buffer computing process includes the merger of overlay areas (dissolve) we cannot predict its exact duration (we do not know how many polygons will touch each other a priori). This is why the gvSIG geoprocessing extension does not show us a progress bar as such, it shows us a bar which periodically reaches the end and then goes back to the beginning. This type of process is called an “indeterminate” process.

Lateral buffer

Lateral Buffer

Select "lateral buffer" from the proximity geoprocesses and click "Open Geoprocess" to show the form related to this geoprocess:

The form is divided into the following parts:

• 1. Selection of elements for which buffers will be calculated. From the drop-down list select the vector layer on which to apply the calculation. Optionally, select the "Use selected features only" checkbox to restrict the calculation of buffers to the currently selected items in the specified layer.
• 2. Definition of the characteristics of the buffers to be calculated. You can either enter the buffer distance (in the first text entry box) or specify a field in the input layer which contains the buffer distances to apply. This second option allows you to apply different buffer sizes for different vector elements (whereas the first option applies the same buffer size to all elements of the input layer).
• 3. Selecting the number of radial buffers and the type of lateral buffer. gvSIG's "lateral buffer" geoprocess allows you to generate various buffers equidistant from the original geometry (for example, if the buffer distance is set at 200 metres and two radial buffers are specified, the second buffer covers the distance of 200 to 400 metres from the geometry. Currently, for reasons of efficiency, the number of concentric radial buffers that can be generated is limited to three. Select lateral gives you the option to create the buffer to the right or the left side of the geometry, as defined by the direction the geometry was digitised.
• 4. Details of the result layer. The outputs from this geoprocess can only be saved as shp files. For this reason, gvSIG provides options for selecting an existing shp file to overwrite, or for specifying a new shp file and path.

Once all the information necessary to calculate the buffer has been entered and the "OK" button is clicked, the input information is checked to verify if it is correct.

If the input information is correct, a dialog with a progress bar indicating the progress of the calculation of the lateral buffers is displayed.

Intersection

Introduction

This geoprocess operates on two layers, the “input layer” and the “overlay layer”, whose geometries can be polygons, lines or points.

It calculates the intersection with the different geometries in the “overlay layer” for each geometry in the “input layer”, thus creating a new element for each intersection. This element will take all the alphanumerical attributes in the geometries that created it (input and overlay). This is why (it models space areas which comply with the condition of belonging to the two polygons, lines or points that created it) this geoprocess is known as “Spatial AND" operator.

An example of how this geoprocess can be applied:

Given a land use layer (e.g. Corine2000), and a national geological map layer, you can obtain a polygon layer with homogeneous information on land use and geological material.

Running the 'Intersection' geoprocess

After selecting the "Intersection" geoprocess, the following dialogue appears:

Select the input layer and the overlay layer. You must also specify a file in which to save the results. Finally, click on "Ok" and the geoprocess will be run.

In this case, we will use a very simple example to better understand the function of the geoprocess. The previous figure shows two overlaying polygons. The result of launching the “Intersection” geoprocess with these layers as parameters is as follows:

Clipping

Introduction

This geoprocess allows you to limit the working area of a vector layer (points, lines or polygons), and to extract an area of interest from it.

To do so, you need an “input layer” (the layer you will use to extract an area) and a “clipping layer” so that the union of the geometries included in the "clipping layer" defines the working area.

The geoprocess checks all the vector elements in the “input layer” and will calculate the intersections for the vector elements contained in the working area defined by the “clipping layer”, so that in the "result layer" only the vector elements of our working area will appear. The geometry portion that lies outside the working area will be clipped. The alphanumeric schema of the input layer remains intact.

Examples of use:

Setting up a local GIS would allow you to include national or regional maps and then to delimit the city or town as the working area.

Running the 'Clipping' geoprocess

When the "Clip" geoprocess has been selected, the following dialogue appears.

This dialogue allows you to select which layer you wish to clip, and gives you the chance to only clip the elements which are selected in the layer.

It allows you to select which layer will be used as the clipping layer and whether you wish to use the union of all the polygons in the clipping layer as the clipping polygon or just the selected elements.

Finally, as in the case of the other geoprocesses in gvSIG's geoprocessing extension, you can define how the result layer will be saved (at present you can only save it as a shp file).

As a result of running the geoprocess, you will have a new layer in which only the geometries which came under the union of the clipping geometries have been kept.

Dissolve

Dissolve

This geoprocess only acts on one “input layer”. The process analyses each entity in the "input layer" and merges the elements that have an identical value for a specific field into one element. Moreover, it allows you to involve spatial criteria in the decision to merge several features. This allows you to establish that for two elements to be merged, they must be adjacent to each other in addition to having the same value in the specified attribute.

Example: We have a polygon layer which represents the municipalities of a particular autonomous region and we need a polygon layer with the provinces which make up this region. We can generate a province layer by launching the “Dissolve” geoprocess and specifying that the polygons that have the same value for the "PROV" field in which a unique code for the province is specified are merged.

Running the 'Dissolve' geoprocess

Using the previous example, we start by taking a "local layer" which we wish to convert into a "provincial layer".

When the "Dissolve" geoprocess has been selected, the following window appears:

Firstly, select the layer you wish to dissolve (you can only work with a selection of elements in this layer).

You then need to specify the attribute of this layer which is going to be used as the criterion to merge the adjacent polygons. In our example, we must choose the “PROV” attribute.

The polygons to be merged must have the same value for the dissolving attribute and in addition, you can choose whether they are adjacent to each other (spatial criteria). If you wish to choose this option, enable the "Only dissolve adjacents" check box. The gvSIG geoprocessing module allows you to keep a summary of the input layer polygon attributes once they have been merged. To do so, the “Summary function” concept is introduced. As each polygon of the “Dissolve” geoprocess result layer is the product of joining several input layer polygons, a summary function on the numerical attributes of the merged polygons can be applied.

If you click on the button with the "<-" icon, a dialogue will be shown in which you can choose one of several summary functions for a selected attribute.

The summary functions supported are maximum, minimum, average and summatory. A field will be included in the result layer for each summary function selected for the numerical attributes you have selected a summary function for.

When you have specified the field you wish to merge and the numerical attributes you wish to obtain a summary value for in the result layer, you are ready to run the geoprocess.

Split lines

Trim Lines

The functionality provided by this geoprocess is to cut a line into sections of equal size. To access this geoprocess click on the geoprocesses that transform data and choose "Split lines". Click on "Open geoprocess" to display the following window:

Enter the following data:

• Input cover: The Layer to be cut into into sections of equal size. You can also activate the "Use selected features only" check box to restrict the line cutting to selected lines only.
• Distance section: Enter the length of the new lines.
• Output cover: Enter the name and path of the layer for saving the changes. You can check that everything is correct by creating a field and then calculating the lengths of the new lines by means of the field calculator. Note that the last line section will not necessarily be the specified length, but will have a length less than or equal to the desired length.

Merge

Introduction

This geoprocess acts on one or several layers, generating a new layer which joins all the geometries in the “input layer”. The "result layer" of this geoprocess will keep the attributes of the "input layer" specified by the user. For the rest of the layers which have not been selected, the attributes whose name and type of data coincide with any of the attributes in the selected layer will be kept.

Example:

When a cartographic series arrives which is separated into sheets and you wish to join the content of the different sheets in one layer. This is the case of the Magna series of sheets, published by the Spanish Technological and Geomining Institute (ITGME).

Running the 'Merge' geoprocess

If you select the “Merge” geoprocess, the following dialogue appears:

The geoprocess allows any of the layers loaded in the layer tree in the gvSIG active view as an input layer. To run the process, first select the layers you wish to merge in the "Input layers" text box. Then, click on the "Select” button. A new window will open in which you can give the new layer file a name or choose a target file.

Click on the "Save" button when you have finished and gvSIG will return you to the geoprocess window. Click on the "Ok" button. This will start the geoprocess.

A new layer will be created at the end of the process which will be added to the view.

However, in the example of the sheets in a cartographic series, it would be awkward to load all the pages in the series one by one. Thus, there is an extra option to select a directory and to add all the layer files (with extensions supported by gvSIG) contained in this directory to the geoprocess input layer list. The only layer files currently supported are shp format files. If you click on the “Folder with files...” button and select a directory, a list of the layer files contained in it are shown and can be selected as part of the geoprocess input layers.

Until you select at least one layer to merge with one of the two possible lists (the layer list in the gvSIG layer tree and the layer list contained in the specified directory), no layer will be shown in the pull-down list. This list allows you to select which layer is going to define the attributes of the result layer’s attributes. When you select the layers to merge in one of the two lists, the layer whose attributes we wish the result layer to have and when you have specified the file you wish to save the result layer in, you can run the geoprocess. An initial requirement is that all the geoprocess input layers have the same type of geometries.

The result will be a new layer with all the input layer geometries.

Convex hull

Introduction

This geoprocess calculates the “Convex hull”, or the smallest convex polygon which surrounds all the vector elements in an “input layer”.

It only works with an “input layer” whose geometry type can be any type (point, line or polygon). There are different types of applications for this geoprocess: Determining the coverage area for a specific geographical phenomenon.

Calculating the diameter of the area covered by a series of geometries, etc.

Creating a convex hull

If you select the “Convex hull” geoprocess, the following dialogue appears:

After selecting the layer whose “Convex Hull” you wish to calculate and specifying an shp result file, you can run the geoprocess and generate a new result layer.

The following image shows the convex hull created which surrounds all the points in the input layer.

Difference

The 'Difference'

The “Difference” geoprocess works with two layers, the “input layer” and the “overlay layer”. It is known as “Spatial NOT” and allows you to obtain the areas in a layer which are not present in the other layer. The geometries in both the “input layer” and the “overlay layer" must be polygons, lines or points. The alphanumerical schema of the “input layer” will remain intact in the "result layer", as in the end it gives more information about it.

This geoprocess is very useful in numerous situations. For example, it can be used to complement the "Clip" geoprocess. If “Clip” allows you to exclude everything that does not belong to a geographical area under study, "Difference" allows you to do exactly the opposite; exclude a specific area from our working layer.

A useful example:

Transferring territorial jurisdiction between different governing bodies. Thus, if the national government transfers certain jurisdiction to a regional authority, it can decide to exclude the geographical area of the transfer in question from its data bases.

Running the 'Difference' geoprocess

Running the “Difference” geoprocessClick on the “Open Geoprocess” button to access the dialogue window which allows you to run the "Difference" geoprocess.

You can enable the “selected features” check boxes at this point of the geoprocess for the input layer and the overlay layer. If you click on the “Ok” button, the geoprocess will be run.

In the following image, the “Difference” geometry appears in black between a flood zone and one of the selected cities or towns. In this case, the new layer resulting from the calculation of the difference will take the schema (alphanumerical attributes) of the geoprocess input layer.

Union

Introduction

This geoprocess is similar to the “Intersection” and "Difference" geoprocesses in that it operates on two polygon, line or point layers to obtain their intersections (this is why these three geoprocesses are known as “overlay geoprocesses”).

The "Union" geoprocess is known as "Spatial OR", because the result layer is made up of the geometries which appear in the two layers (intersections between the polygons, lines or points), plus the geometries which only appear in one of the two associated layers.

This means that the geoprocess carries out three analyses:

the first time it calculates the intersection of both layers, the second time it calculates differences between the first layer and the second, and the third time it calculates the differences between the second layer and the first.

This geoprocess may be of interest if you wish to generate new layers which show the occurrence of two phenomena so that the occurrence of one of the two or of both is highlighted.

Running the 'Union' geoprocess

If you select the “Union” option, the following dialogue appears:

When you have selected the input layer, the clip layer and an output layer, click on "Ok".

The result layer will have all the intersections and differences between the two layers. If you click on the “Information” button and then on the different polygons in the result layer, you will see that the intersections have all the attributes, whilst the differences only have the attributes of the layer that created them.

Spatial join

Introduction

This geoprocess allows you to transfer the attributes of one layer to another based on a common element. In contrast to the join sql operator in the relational data bases, in this case, the common element is not that a field of the two tables takes the same value, but that the related elements in the two layers meet some spatial criteria.

The “Spatial join” geoprocess allows you to follow two types of spatial criteria to establish the spatial link:

Nearest neighbour (1->1 relationship). This assigns the attributes of the nearest element in the related layer to an element in the source layer.

If the nearest element intersects (or in the case of polygons is “Contained in”) with the source element, the algorithm will take the first element analysed in the possible intersections.

Contained in (1->M relationship). This relates an element in the source layer with several elements in the destination layer (in particular, with those that intersect).

In this case, the source layer will not inherit the related layer’s attributes, but the operation will be very similar to the "Dissolve" geoprocess.

The user can choose one or several summary functions (average, minimum, maximum, summatory) to be applied on the numerical attributes of the related layer for the M elements related to an element in the source layer.

Running a 'Spatial Join'

When you have selected the "Spatial join" option, the following window appears:

This window is practically the same as the windows in the overlay geoprocesses (Union, Difference, Intersection) with one difference.

It allows you to choose whether you want to run a 1-1 relationship (using the nearest neighbour spatial criterion) or run a 1-N relationship (using the “Intersect” or “Contained in” spatial criterion).

The choice can be made by enabling or disabling the "Use nearest geometry" check box. If when you have selected the source layer and the layer to be related, the geoprocess is launched and you have not enabled the "Use nearest geometry" check box, a window appears in which you can select the summary functions you wish to apply for each numerical attribute of the layer to be related:

The summary functions are the same as in the “Dissolve” geoprocess:

Thus, the attributes transferred to the source layer will be the result of the summary functions selected for each numerical field. If you run the geoprocess and the “Use nearest geometry” option is enabled, this window does not appear.

2D Translation

Introduction

This geoprocess allows a translation transformation to be applied to all the points, lines and polygons of the geometries in the input layer. The geoprocess can be applied to all types of vector layers (shp, dgn, dxf…). To do so, the movement on X and Y must be specified.

This geoprocess is extremely useful when combining cartographies which come from different sources, a process which is referred to as conflation. Bear in mind that although translations can be carried out on all types of vector layers (shp, dgn, dxf, dwg…), the resulting output layer will always be a shape file. In other words, the input layer can be a shp, dxf or dgn file, but when translation is applied to these layers, the result will be one or various different output layers which are always shape files.

When a translation is carried out in which the input layer is a vector layer which is not a shape file, the result of the translation will be three layers in SHP format (one line layer, one point layer and one polygon layer).

If, for example, the input layer to which the translation is applied contains only points and lines, the polygon .shp file will be created but it will be empty.

NB. At the end of this section there is a table giving details of the relationship between the type of input file and the resulting output layer.

Translating a vector layer

Firstly, load a vector layer in gvSIG and then click on the geoprocessing wizard in the tool bar.

Select the option “2D Translation” from the “Data Conversion” folder. Click on the “Open Geoprocess” button and the geoprocess data input window opens. For the input layer, select the vector layer (dgn, dxf, dwg, shp…) you wish to translate and introduce the values corresponding to X and Y. Select an output layer and click on “Ok”.

The following image shows the result of applying the translation process.

Relationship between the type of layer before and after translation.

Input cover		Output cover/s
Point Shp file		Point Shp file
Multipoint Shp file		Multipoint Shp file
Line Shp file		Line Shp file
Polygon Shp file		Polygon Shp file
Dxf (points, lines, polygons)		Point Shp file Line Shp file Polygon Shp file
Dgn (points, lines, polygons)		Point Shp file Line Shp file Polygon Shp file
Dwg (points, lines, polygons)		Point Shp file Line Shp file Polygon Shp file

Reprojection

Introduction

This geoprocess allows you to change the geodesic projection of the vector elements in the input layer. In order to do so, the user must specify the new projection to be applied.

This process is extremely useful when standardising cartographies in the same project if these are in different projections.

Reprojection of a layer

Click on the geoprocessing wizard in the tool bar and select the “Reproject” option from the “Data conversion” folder.

Click on “Open geoprocess”. The wizard will open to guide you through the reprojection process.

In “Input layer”, select the layer you wish to reproject from the layers loaded in the ToC.

To select the new projection for the layer, click on the button next to the destination projection and select the new reference system.

Exporting layers

Introduction

The “Export to...” tool allows you to save the elements selected in a layer in a different format. If no elements have been selected the whole layer will be exported. At the time of going to press the export formats supported by gvSIG were shape, dxf, and postgis and gml.

Exporting a shape

Select the “Layer” option from the menu bar then go to “Export to…/shp”.

If you have selected elements in the layer to be exported, gvSIG will tell you how many elements are going to be exported and will ask for confirmation before carrying out the operation.

If you continue with the operation, a dialogue box will appear in which you will be asked to select the file the new shape is to be saved in.

When you have accepted, a new message will appear asking whether you wish to insert the new layer into the view.

If you click on “Yes”, the layer will be added to the active view.

Exporting to dxf

Select the “Layer” option from the menu bar then go to “Export to…/dxf”.

Follow the same process used for exporting to shape.

Exporting to postgis and Oracle Spatial

Desde la barra de menú seleccione la opción “Capa/Exportar a.../postgis”.

Si tiene elementos seleccionados le mostrará una ventana informándole del número de elementos que se van a exportar (al igual que en exportar a shp y dxf).

Si pulsa sobre la opción “Sí” para continuar la exportación gvSIG, aparecerá un diálogo donde podrá seleccionar una conexión a PostGIS activa o crear una nueva.

A continuación podrá seleccionar el esquema (entre los existentes en la base de datos actualmente) y el nombre de la tabla donde debe guardarse la exportación. Recuerde que si la tabla existe en la base de datos, la información que contenga será borrada.

Cuando haya introducido el nombre de la tabla pulse el botón “Aceptar” para comenzar la exportación

Exporting to gml

Select the “Layer” option from the menu bar then go to “Export to…/gml”.

Follow the same process used for exporting to shp or dxf.

Exporting to kml

From the menu bar, select Layer > Export to... > Keyhole Markup Language (KML).

From here on the steps are exactly the same as for the Exporting to GML option.

Annotation layer

Introduction

This gvSIG tool makes advanced labelling easy.

The process creates a new layer which represents annotations.

The main features of this new layer can be summarised as follows:

• The new layer is only composed of the annotations created.
• The table associated with this new layer only contains the fields which refer to the text of the annotations (Text, Font, Colour, Height and Rotation).
• The layer created is always in .shp format, irrespective of the format of the original layer.

Creating an annotation layer

To create an annotation layer, first select the layer from the ToC (Table of Contents).

In the menu bar, select the “Layer” option, then select “Export to” and finally select the “Annotation” option.

This option opens the wizard which will guide you through the steps required to create the annotation layer.

In the wizard’s first window, select the data which gvSIG requires to carry out the operation from the pull-down tab:

Duplicate control: Select either “None” or “Centred” to choose the position in which you wish the annotations to be inserted.

Centred: A label is created for each value and this will be inserted in the centre of all the labels which are the same.

None: A label is inserted for each value, even if these are repeated.

Select the field to be labelled: Choose the field which contains the text you wish the labels to show.

If you do not wish to modify the format of the annotations created by gvSIG and prefer a standard format, click on “Finish”. If you wish to customise the format, click on “Next”.

The wizard’s second window allows you to select the fields of attributes of a a table (if there are any) which contain the values which allow you to customise the labelling.

The following parameters can be customised.

Slope – the slope the annotation will have in the view.

Colour – annotation text colour.

Height – annotation text height.

Units – units in which the value assigned to the “Height” field are to be measured.

The options currently available are map units or pixels.

Font – annotation text font.

Set the values to be used for customising the required parameter (by pulling down the list).

Leave the default value in the fields you do not wish to customise.

Click on “Finish” when you have input these changes.

Editing an annotation layer

An annotation layer can be edited like any other layer. To start an editing session in gvSIG, select the layer in the Table of Contents and then select the option “Start edition”.

When you start an editing session, an option appears in the menu bar called “Modify annotation”. This will allow you to individually customise the annotation you wish to change.

When you click on this button, the appearance of the cursor will change. You may graphically select the annotation by clicking on the point associated with the text and then access a set of properties shown in the following image.

Annotation layer properties

If we select the “Properties” option from the annotation layer contextual menu, the following box appears:

The “Layer properties” box has two tabs. The “General” tab allows you to access the general properties of the layer and the “Annotations” tab allows you to select: whether you wish the annotation text to be shown in pixels or metres in the view.

Whether you want only the text to appear (select the “Draw text only” option) or if you prefer the text to be accompanied by a location point (deselect the “Draw text only” option).

However, remember that this point is useful, for example, to move the annotation or to access the “Modify annotation” window.

If you wish to avoid overlays, activate the “Avoid overlays” option.

If you wish to eliminate overlaying annotations, activate the “Clear overlaying annotations” option.

Adding an annotation layer to the view

To add an annotation layer, click on the “Add layer” button in the tool bar

and select the “Annotation” tab.

In the box you can select the annotation layer you wish to load, in addition to the units in which the annotations are displayed (pixels or metres) and the projection of the layer.

Example of how to create an annotation layer

The following image shows how an annotation layer is created out of a polygon layer called “muni10000.shp” which contains all the towns in the Valencian Region.

In the first window of the wizard, insert the type of duplicate control you wish to use and select the field which contains the text to be shown.

This is the field in a layer’s table of attributes which contains the name of the town.

If you do not wish to customise the presentation, click on “Finish” and indicate where you wish the new annotation layer to be saved.

The following image shows the result (the rest of the fields in the wizard are left with their default values and this one is zoomed in) of creating the “annotation layer”.

The annotation layer which has been created is the one in red called “Towns” in the Table of Contents.

Export to a raster layer

This tool allows you to extract portions of a raster layer using a selection in the view or by inputting the coordinates that define the portion to be extracted.

It allows the user to change the spatial resolution of the clipping or of the whole image, choose the bands to be extracted or generate a new raster layer for each of the original bands.

To access this option, go to the ToC and select the raster layer you wish to select a portion of.

Then go to the Layer/Export to menu and select the “Raster” option.

The following window appears:

Image clipping

There are two ways of selecting an area to be clipped from the original raster layer:

You can use the text boxes in the window to input the data which correspond to:

• Real coordinates: If the source image is georeferenced.
• Pixel coordinates: If the source image is not georeferenced.

You can also make your selection directly from the view by clipping the whole image or selecting a part of it.

This button allows you to obtain a clipping from the whole image.

This button allows you to obtain a clipping from a selected area in the view. Place the cursor over the image, then click and drag. Check that the text boxes are automatically completed.

If you wish to save the raster layer clipping you have created, click on “Save” and select the location you wish to save this file in. The image will be saved in TIF format.

Changing spatial resolution

The controls that allow you to specify the clipping’s (or whole image) spatial resolution are located in the Clip table, with the additional options panel pulled down (to pull this panel down click on the button). You can define the resolution by specifying the Cell size or the Width and Height of the raster layer to be generated in pixels as well as choosing the interpolation method using the resolution change. At the moment, only the “Nearest neighbour” option is operational.

Band selection

The original raster layer’s band list appears at the bottom of the Clip table. You can use this list to choose the bands the output raster layer will have if you enable or disable the check boxes in the Bands column. If you check the Create one layer per band option, a new layer will be generated for each of the bands checked in the list. The new layers will be added to the ToC.

Saving and Adding a raster layer clipping to the current view.

When you have established all the parameters which define the raster layer clipping you have made, click on “Save”. This opens a dialogue box which allows you to search for a directory to save the clipping in. If you wish to add the layer to the view, go to the “Add layer” button in the tool bar once you have saved the clipping.

Example of a raster layer clipping

This example shows how a clipping is taken from an orthophoto.

First, select the area by defining a rectangle in the gvSIG view.

When you have finished, the coordinates will automatically be input into the text boxes based on the selection. You can fine tune these selected values from the view by inputting the new value directly into the text boxes containing the data.

Then pull down the box. As the resulting image is to be resampled, not as much resolution is required. Therefore, go to the “Spatial resolution” section and select “Width x Height”. This enables the text boxes so that you can input the output raster layer resolution.

When one value is input the other one is automatically completed when you press Enter or when you exit the field, as the proportions between the width and height must be maintained.

The cell size for the chosen output resolution is also calculated. If “Cell size” had been chosen, you would have had to specify the size in metres for each pixel and thus the width and height for the chosen cell size would have been calculated.

You now need to select the bands you want the output layer to have. In this case, select them all as this is a three-band orthophoto and we want to include them all.

Finally, for our example, the “Create a layer per band” option needs to be enabled to do just this.

Each new layer will have the same data type as the original image. If you click on “Save” a dialogue box opens to indicate the directory and image name.

To retrieve the layers you have created, go to the Add layer” button and then to the directory they were saved in.

Creating a layer with derived geometries

"New layer with derived geometries" tool.

This tool allows users to generate geometries derived from points or lines in a vector layer, and to store them as a new shape layer.

Table

Icon	Description
	Derived geometries tool enabled if the TOC contains at least one visible point or line vector layer that is not in edit mode.
	Derived geometries tool disabled if the TOC does not contain any visible point or line vector layers that are not in edit mode.

The tool can be accessed from:

Via the menu: Layer / Derivative geometries

Layer selection dialog and process

Upon choosing the tool a dialog for selecting layers is displayed:

1. Source Layer: drop-down list of point or line vector layers in the current View that are not in edit mode. Select a layer to be the source layer.
2. Name of the output layer: layer name that will appear in the TOC.
3. Path of the output layer: full path for creating the new shapefile.
4. Type of output layer: geometry type of the new layer. This depends on the type of process chosen (See options below).
5. Type of process: select the type of geometry generation process. This depends on the geometry of the source layer. This process is applied to the source and destination layer pair until the tool is closed.
6. Cancel: Close the tool.
7. OK: Opens a control panel and displays data for the selected source layer. This control panel will be associated with source and output layers until it is cancelled.

Table

Source layer geometry type	Type of process	Target layer geometry type
Points	Points to line	Lines
Points	Points to polygon	Polygons
Lines	Close polylines	Polygons

Process Control Panel

The control panel is associated with the layer and is shown every time the layer is activated in the TOC, as long as the layer is visible and not in edit mode.

The dialog has a semi-modal behavior in order to allow the user to continue working with gvSIG by using the minimize, maximize, resize and hide buttons (use the X, not the Cancel button, to hide the dialog).

1. Name of the source layer: Layer from the TOC that contains the source geometries.
2. Name of the output layer: Name of the new derived geometry layer that will appear in the TOC.
3. Table of features: Table showing the attributes of all the source layer's features. Source layer geometries selected in the View will also be selected in this table.
4. Add all: Adds all the features of the source layer to the table of selected features.
5. Remove all: Removes all features from the table of selected features.
6. Enable snapping tool: Enables snapping tool on the source layer, without putting it into edit mode (only available in the Castilla y León extension for gvSIG 1.1.2).
7. Add selected features: Adds only the selected features to the table.
8. Remove selected features: Removes only the selected features from the table.
9. Table of selected features: Table showing the attributes of all the features selected from the source layer. It has 2 extra columns:
   • Order: Order to be used when generating the new geometry from the selected features in a point source layer, or when closing polylines in the case of a line source layer. The order can be changed with buttons 10 and 11.
   • ID: Fixed ID number of the geometry in the vector layer.
10. Move up: Moves the selected geometries up one position.
11. Move down: Moves the selected geometries down one position.
12. Create: Start the process of generating the derived geometries. If it doesn't already exist, a new layer is created, and the new geometries are added to this layer. The process is done in a thread, the progress of which is indicated by a progress bar.

The results of the completed process can be viewed by clicking on the "View Details" button. There are three types of data that are of interest here:

• Number of geometries to create: depends on the geometry selected:
  • If they are of type point: one line or polygon is created.
  • If they are of type line: one polygon is created for each line.
• Number of geometries that could not be created: the subprocess failed, for example because a polygon couldn't be derived from simple lines that consist of only two points.
• Number of geometries created successfully: the new geometries created.

This information is recorded in the gvSIG log.

The control panel is hidden during the process but becomes visible again when the progress dialog is closed.

13. Cancel: Closes the control panel and de-registers the associated tools, thereby terminating the tool for the specified source layer.
14. Expand / Collapse: Changes the position of the splitter, so as to display only the table of features, only the table of selected features and associated management controls, or both halves of the control panel interface.

Control Panel Behaviour

The control panel is linked to the source layer from the time it is created until it is cancelled by clicking the cancel button.

Table

Action	GUI Element	Description
Maximize		Resizes the dialog so that it fills all available space.
Minimize		Minimizes the control panel to a restore button.
Collapse		Control panel is hidden but remains linked to both the source and output layers. Further operations between these layers can be performed once the panel is restored.
Resize		The size of the control panel can be increased or reduced by selecting and dragging the edge of the panel.
Expand / Collapse splitter interface		These controls are used to display only the table of source layer features, or only the table of selected features and associated management controls, or both halves of the control panel interface.
Cancel		Closes the tool so that is no longer available for operations between the source and output layers.

When the control panel is hidden it can be restored it by clicking on the source layer in the TOC.

If the View is closed when control panels are visible, the panels will be hidden and then restored when the View is reopened.

Geometries derived from points do not retain any attribute values but do maintain the columns. Those derived from lines, keep all attributes.

Removing the new layer associated with control panel will result in the tool being ended and a warning being displayed to the user.

Examples

This example will show how to generate a line layer showing the path followed from home to work, and back again. The example uses the following four shape layers:

• Land-use: layer showing parcel boundaries of the town.
• Rivers: layer showing rivers in the town.
• Lakes: layer showing lakes in the town.
• GPS Waypoints: shape layer containing points recorded by a GPS on the drive to and from work. This layer will be used as the source layer in the example.

Once all four layers have been loaded the "Derived Geometries" tool can be selected and the following values entered:

• Source layer:
  • Layer: GPS Waypoints
• Output Layer:
  • Name: Route: Work to Home
  • Path: .../RouteWorkToHome.shp
  • Type: Lines
• Options:
  • Mode of operation: points to line

When "OK" is clicked the new process control panel appears. If a file with the same name as the new output layer already exists then the user is asked whether to continue or not. If yes, then the file will be overwritten.

Minimizing the control panel will reveal the View:

The geometries can be selected from the top table in the control panel.

We select the first seven geometry points (1st route: work to home).

Click "Create" to generate the first path:

Modify the symbology so that the route stands out as a thick line.

To generate the route back, activate the control panel and select the remaining points from the source layer so that the line can be generated:

Finally suppose we are interested in the polygon formed by the closure of the routes.

Cancel the tool and then reopen it but this time use the new layer as the source:

• Source layer:
  • Layer: Path: GPS Waypoints
• Output Layer:
  • Name: Close routes
  • Path: .../CloseRoutes.shp
  • Type: Polylines
• Options:
  • Mode of operation: close polylines

Select all the geometries (the two polylines) and generate the polygons.

Since the layer "Route: Work to Home" does not contain data due to the points to line process, we assign a distinguishing identifier to each by editing the layer.

Now apply some changes to the symbolology:

• Layer "Close routes": select a unique values symbology to distinguish the two polygons, and choose fill patterns that allow the lower layers to be seen.
• Layer "GPS Waypoints": Use a symbol of a car for the points and place the layer above the other layers.

Raster

Layer functionalities

Filters

Description

Filtering is a process by which we can enhance images. gvSIG can filter images through a variety of filtering methods. In the upper left part of the Filter dialog, the filters are grouped by type (1). By double-clicking one of the filters or by clicking on the "Add Filter" button on the bottom left, the filter will be added to the list of filters in the lower left part of the Filter dialog. All filters in the filter list will be applied in the preview. If you want to remove a filter from the list, you can either double-click on the filter or click on the "Delete filter" button. The filters in the list will be applied to the image in the order that they appear. Keep in mind that the order in which the filters are applied will affect the result, and changing the order of the filters may change the output.

In the middle of the dialog window are the controls of the selected filter (2). When changing the controls of one of the filters from the filter list, the results will be directly shown in the preview window. Below the middle part of the dialog you can change the name of the output layer that will be generated when clicking "Apply" or "Close".

On the right side of the dialog you can preview the outcome of the filters (3). (See documentation on "Preview tool"). In the lower right part you can select whether you want to display the filters over the selected layer or save the filtered image as a new layer (4).

The button "Apply" will apply the changes according to the entered parameters, keeping the Filter dialog open. The "Close" button will apply the changes and close the Filter dialog. The "Cancel" button will close the Filter dialog without applying any filters.

All filters in the filter list can be activated or de-activated through the "Active" checkbox. This checkbox is usually located in the upper part of the filter control panel.

Enhancements

The brightness filter changes the brightness value of the layer. You can increase or decrease the brightness by moving the position of the sliding bar or by entering the value directly in the text box and press enter.

The contrast filter changes the contrast value of the layer. You can increase or decrease the contrast by moving the position of the sliding bar or by entering the value directly in the text box and press enter.

Spatial filters

With this type of filter, graphical transformations like smoothing, edge detection, sharpening etc. are applied to the image.

The following filter types can be applied:

MEDIAN FILTER

The median filter applies a kernel of a certain size, which is determined by the user through the sliding bar labeled Window side.

The median filter is normally used to smoothen and to reduce noise in an image, by moving a kernel of N x N number of pixels over the image and evaluating each central pixel, replacing its value with the median of its neighboring pixels. Compared to the Mean filter, the advantage of the Median filter is that the final pixel value is a value that actually occurs in the image and not an average.

MEAN FILTER

The mean filter applies a kernel of a certain size, which is determined by the user through the sliding bar labeled Window side.

The filter replaces the value of the central pixel with the mean value of the surrounding pixels. Each value of the kernel would be one and the divider would be the total number of elements in the kernel (i.e. a kernel of 3 x 3 would replace the value of the central pixel by the average value of the nine pixels covered by the kernel).

LOW PASS FILTER (smoothing filter)

The low pass filter applies a kernel of a certain size, which is determined by the user through the sliding bar labeled Window side.

Using a low pass filter tends to retain the low frequency information within an image while reducing the high frequency information.

SHARPENING FILTER

By moving the slider to change the sharpness (values from 1-100), the contrast of an image can be changed. The results can be evaluated in the preview window. With a higher contrast, details in the image can be accentuated but the noise will also increase.

GAUSS FILTER

The Gauss filter applies a kernel of a certain size, which is determined by the user through the sliding bar labeled Window side.

The maximum value appears in the central pixel and gradually decreases for pixels that are further away from the central pixel.

CUSTOM FILTER

This is a kernel of 5 x 5 or 3 x 3, for which the values can be introduced by the user. After multiplying the pixel values with the kernel values, the result will be divided by the number specified in the Divisor textbox.

MODE FILTER

The mode filter applies a kernel of a certain size, which is determined by the user through the sliding bar labeled Window side.

This filter takes the value that occurs most in the surrounding pixels and assigns it to the central pixel.

Colour adjustment

Edge detection

These filters attempt, through the use of kernels, to detect edges in the image and change the image so that these edges are enhanced, while the rest of the image is grayed out.

There are four edge detection filters, all with the same interface and options, in which the user chooses a threshold in the range 0-255, and the possibility compare the results by ticking the compare check box:

SOBEL

The Sobel filter detects the horizontal and vertical edges separately on a grayscale image. Colour images are converted to RGB gradations. The result is a transparent image with black lines and some remains of colour.

ROBERTS

The Roberts filter is suitable for detecting diagonal edges. It offers good performance in terms of location. The major drawback of this filter is its extreme sensitivity to noise and therefore has poor detection qualities.

PREWITT

The Prewit filter detects edges in all directions as it consists of 8 kernels that are applied over the image pixel by pixel.

FREI-CHEN

The Frei-Chen filter processes the neighbouring pixels as a function of their distance from the pixel that is being evaluated. The result is that edges in all directions are detected.

Masks

Histogram

Description

To launch the histogram dialog window, use the drop-down toolbar selecting the "Raster Layer" button on the left and "Histogram" in the drop-down button on the right. Make sure that the text box that displays the current layer is set to the name of the raster layer for which you want to see the histogram.

The Histogram dialog shows a histogram of the statistical distribution of pixel values in the current view. This information is often useful when you are trying to color balance an image. In the middle of the dialog you will see the graph on which you can right-click to show a context menu with general options for this kind of graphics.

In the upper part of the dialog (1) are the controls to configure the histogram:

Preferences

The Raster section of the Preferences dialog contains the option "Number of classes" where you can set the number of intervals in which the histogram is divided when the data type of the image is not Byte. For Byte images, this value is 256. In the preferences dialog, the default value of this option is 64 but you can choose any of the options (32, 64, 128, and 256). The intervals are the parts in which the range of values is divided. For example, if we have a DTM with values between 0 and 1 and there are 64 intervals, each interval will have a range of 1/64.

The number of classes does not only refer to histograms but also to other functionalities that require a division in intervals of value ranges.

Radiometric enhancement

The maps that are obtained through digital processing of satellite imagery are useful not only for thematic mapping, but also as a backdrop on which map features can be overlaid. If the visible bands are displayed in a colour composition through the colouring of each band with the corresponding colour gun, it is important that the bands are sufficiently enhanced so that the colours appear more natural. The final display colour depends not only on the direct result of the chosen colour composition but also on the radiometric post-processing. The satellite image map will be more useful as backdrop if the bands are enhanced and displayed in colours that match the natural colours as the human eye perceives them. gvSIG provides the enhancement tools to adjust the colours for each band.

In the following sections the different parts of the dialog are described:

Save View as image

The tool for exporting the view as an image can be accessed from the drop-down toolbar by selecting "Export to raster" on the left button and "Save view to georeferenced raster" on the right button. Make sure that the name of the raster layer that you want to export is set as the current layer in the text box.

A message will appear to inform that you can use the selection tool to set the area in the view to export.

Now, you can select two points in the view to define the rectangle of the area to be exported, by clicking the first point and dragging the mouse towards the second point, then release.

Then, the Save view to georeferenced raster dialog will appear. If the selected area is too small, the dialog will not appear and a bigger rectangle must be selected.

The upper part of the Save view to georeferenced raster dialog shows the coordinates of the two points that define the selected area in the view. You can edit the coordinates to change the selected area.

In the option box in the central part of the dialog you can choose from three selection methods:

• Scale. Selecting this option will enable the Scale textbox and the pull-down box "Spatial resolution" which refers to the resolution in points per pixel (ppp) of the exported image. When entering a value in the Scale textbox and clicking enter, the values "Mts/pixel" and the size (Width and Height) will be recalculated for the output image.
• Mts/pixel (Meters per pixel): When selecting this option, the "Mts/Pixel" textbox is enabled. When you enter a value in the Mts/Pixel textbox and press enter, the values for "Scale" and size ("Width" and "Height") will be recalculated automatically for the output image.
• Size: When selecting this option, the text boxes to enter the "Width" and "Height" will be enabled. When you enter one of these values, the other will be calculated automatically to preserve the right proportions of the image. The other data ("Mtx/Pixel" and "Scale") will also be recalculated automatically. By default, the Width and Height values are displayed in Pixels, but you can select the units (Pixels, Cms, Mms, Mts, or Inches) in which you want to see these values.

NOTE: To save time and memory the maximum size of output images is limited to 20000 x 20000 pixels. If the intended output image is larger and you click on "Apply", gvSIG will display a message that the parameters must be changed before trying again.

Clicking the "Selection" button will open a file browser dialog where you can specify the output file. Depending on the type of file, the corresponding driver will be loaded (you will notice that the button on the right of the "Selection" button will change). For example, an output file .jp2 will open the properties dialog for Jpeg2000. The formats in which you can save are .TIF, .IMG, .BMP, .PGM, .PPM, .MPL, .RST, .JP2, .JPG, and .PNG. Furthermore but only on Linux kernel 2.4 you can also select ECW.

When you select the output file, the Properties button will be enabled.

For example, for geoTiff the dialog will look like this:

• Photometric: [MINISBLACK | MINISWHITE | RGB | CMYK | YCBCR | CIELAB | ICCLAB | ITULAB]. This assigns the photometric interpretation. The default is RGB, as the input image consists of 3 bands of the Byte data type.
• Interleave: [BAND | PIXEL]. By default, tiff files are interleaved by band. Some applications only support interleaved by pixel, in which case you can change this option.
• Compression: [LZW | PACKBITS | DEFLATE | NONE] This refers to the data compression. The default option is NONE.

When the output image is selected and the properties set, you can click on "Apply". A progress bar will appear. Depending on the size of the output file, this process may take while. Processing times may vary between a few seconds or several days, so it is important to check the size of the output image in pixels before clicking "Apply". When finished, a screen with statistics will appear that indicates the path of the output image, the disk size, the duration of the process and whether it was compressed. To check the georeferencing of the output image, you can add it to the view as a new layer with transparency.

Clipping layers

(The clipping tool can be accessed from the raster toolbar by selecting "export to raster" from the left drop-down button and "Clipping" from the drop-down button on the right. Make sure that the raster layer that you want to clip is set as the current layer in the text box.)

With the clipping tool, you can create new layers from an existing one. The options are:

• Extract an area from the input image to be saved as a new layer (cropping)
• Modify the resolution through various interpolation methods
• Modify the order or the number of bands
• Separate the bands into multiple files

Zoom to raster resolution

You can zoom to raster resolution by right-clicking on the layer in the TOC. In the context menu that appears, click "Zoom to raster resolution".

This will activate a crosshair cursor in the gvSIG view which allows users to perform an action by clicking somewhere in the view. The action in this case is that with every mouse-click, the view will be centered on the point where you clicked. In addition, the view will zoom so that one screen pixel is the same size as a pixel in the current raster layer.

Automatic vectorization

The "automatic vectorization" function can be launched from the raster toolbar by selecting "Raster process" on the left drop-down button and "Vectorization" on the drop-down button on the right. Make sure that the name of the raster layer that you want to vectorize is displayed as current layer in the text box.

With automatic vectorization, you can generate a vector layer from a raster image using preprocessing to highlight the features of interest.

When launching the Vectorization dialog, the first step is to select the area of the image that you want to vectorize. Keep in mind that the vectorization process may take a long time, so it is recommended to minimize the area (number of pixels) for vectorization. The selection of the area for vectorization can be done in several ways. You can type the coordinates directly; either in pixel coordinates or in the map coordinates. The area can also be selected from the view by clicking the button "Select from the view", after which you can draw an approximate rectangle to define the area. Another selection option is by Region Of Interest (ROI). You can define a ROI here or use a previously defined ROI to set the area for vectorization. In the section "ROI selection" appears a list of available ROI and a checkbox next to each of these to select one or more ROI that you want to use. There are two options to vectorize the ROI: to vectorize the entire area inside the rectangle (bounding box) that covers all the selected ROI, or vectorize only the areas inside the ROI while considering the values outside the ROI as NoData values, excluding them from the calculations.

Finally you can select the scale of the image to preprocess. This is useful because a higher resolution of the preprocessed image will result in a higher precision for the resulting vector layer. You can define this with the drop-down text box labelled "Output Scale". By default, the resolution will be the same as the input image.

When moving on to the next step of the wizard, the process of cutting the image for preprocessing is started. A progress bar appears with the warning that this operation could take a few minutes. The resulting image cut is saved in the temporary folder of gvSIG.

There are two methods to preprocess a raster image to vectorize. The first is by creating a limited number of grayscale levels from the original image. The image will be converted to grayscale using one single band or a combination of bands (use the drop-down button labelled "Bands"). For the conversion to grayscale, a posterization process is used to reduce the number of different values. (By default, the image is reduced into 2 levels only: black and white.) For this process you can control the threshold on which the values are passing from black to white and vice versa. This can be done by moving the "Treshold" slider while you can see a preview of the result. (The Treshold slider is only available when there are 2 levels; when there are intermediate grayscale levels, the slider is disabled.) In addition to the posterization threshold, you can apply a mode filter or a noise filter to smoothen the result.

The second preprocessing method is useful to vectorize contour lines and can be applied to data types other than byte. With this method you can define intervals between each contour line to be vectorized. You can specify the number of intervals in which you want to divide the raster, or indicate the size of each interval. The cuts that have been selected will be shown on a graph that represents the histogram of the image. On this graph, you can modify the distance between cuts, or add or remove some of them using the mouse. It is also possible to modify the distance between cuts in numeric format using the table on the right of the histogram. Each entry in the table represents a cut with the corresponding value. This type of preprocessing is used for digital elevation models (for example .adf or .asc images).

When moving on to the last step of the vectorization wizard, the preprocessed image is generated with the specified values, and saved in the temporary directory of gvSIG.

The last step is to select the method for generation of vectors. There are two methods: contour and potrace, that can be selected from the drop-down button after which a panel appears with settings that are specific for the method. The first method is the simplest and does not have any options. This method will trace the vectors in straight sections going through the pixel centers. This generates a network of vectors based on very small straight sections. The potrace method uses the potrace library for vectorization. The available options for this method are those that the potrace library provides and they are used to define the precision of the tracing of the curves: number of points for each curve, threshold, optimization, etc.

When clicking on "Apply" or "Accept", the process of vectorization will start after which you will be prompted whether to display the generated layer in the TOC.

Analysis view

The "Analysis view" can be launched from the raster toolbar by selecting "Raster layer" from the left drop-down button and "Analysis View" on the drop-down button on the right. Make sure that the name of the raster layer that you want to analyze is displayed as current layer in the text box.

With this functionality you can zoom in on the current raster layer with 3 different zoom levels:

1. On the left of the view, the layer is added to the locator map of gvSIG. This provides a general view of the layer, and you can zoom into the locator map by clicking and dragging, thus drawing a red rectangle. The area inside the red rectangle will be displayed in the view.
2. The view itself is the second zoom level which functions independently, and the zoom variations that are performed on the view will be applied to the locator map as well so that it keeps being centered on the correct area.
3. When launching the Analysis view, a small floating window labelled "Cursor Zoom" appears in the upper right corner of gvSIG. This window has the highest zoom level. The zoom level is fixed and always centered on the mouse point. By moving the mouse over the gvSIG view, you will see the contents change.

You can change the relation between the zoom level of this floating window and the gvSIG view. This is done by right-clicking on the floating window and selecting one of the values that are shown in the drop-down menu that appears. The available options are x4, x8, x16, and x32. This means that the pixels in the floating window will be 4, 8, 16, or 32 times bigger than the original.

The floating window also shows the RGB values of the pixel on which the cursor is currently located. The text colour of the RGB values as well as the colour of the central cross (red by default) can be changed by right-clicking on the floating window and choosing the option from the drop-down menu.

Keep in mind that, to see the effects in the floating window while moving the mouse over the view, the view must be active. If it is not active, just click on the view. When the cursor is outside the view, the content of the floating window appears black.

There can only be one Analysis view open at any time in gvSIG. Therefore, the button "Analysis View" is re-labelled as "Close Analysis View" when the Analysis view is already open, so that it can be closed before re-opening.

Geographic Transformations

Geolocation

The Geolocation tool provides the ability to change the related transformation that is applied to a raster in its display. A raster could have coordinates that place it in a geographical position. This geographic location is only a change of position, scale and rotation of the image relative to an original position. These changes in position, scale and rotation are those that can be changed with this tool. This can be done numerically and by visual approximation.

This tool does not provide capabilities to deal with complex projections and georeferencing involving the need for resampling.

To launch the geolocation dialogue of the layer, the drop-down toolbar is used by selecting "Geographical Transformations" on the left button and "Geolocation" on the dropdown button on the right. Make sure that the text shows the name of the layer to which we like to assign the transformation.

Upon activating the geolocation tool on a raster layer, a small dialog will appear floating on the view with a series of text entries and a button bar. Also the raster layer that has been selected acquires the capacity to be moved, rotated or moved by clicking and dragging it to the right place on the view.

Georeferencing

Description

Direct traslation from Google traslator

To launch the georeferencing dialog it is used the dropdown toolbar selecting the "Geographic Transformations" button on the left and "Georeferencing" from the dropdown button on the right.

Initially we must decide what type of georeferencing to implement, "reference maps" or "without reference maps".

Modifying georeferencing upon loading

When you load a file that is not georeferenced, gvSIG can prompt you to enter the coordinates manually. For this the option has to be activated in preferences, which is disabled by default. The option that needs to be activated is "Pedir las coordenadas al cargar un raster que no tiene georreferenciación".

In this case we will see a dialog with the message: "Name of layer. The layer has no georeferencing. Do you want to enter them manually?". If you answered "No", the load is carried out with the coordinates (0, 0) in the top left corner (width in pixels, height in pixels) in the lower right corner. If the answer is "Yes", then a dialog to enter the coordinates of the raster will show. In this one must be careful to enter valid data to avoid erroneous results. The dialog has two tabs from which we can enter the coordinates in the form of affine transformation or the upper-left and bottom-right corners. In the first mode will need the X and Y coordinates of the upper right corner of the original raster, the pixel size in X, the pixel size on Y, X rotation and the rotation Y.

In the second mode we only introduce the coordinates of the corners in the order indicated by the graphs.

Image reprojection

For the reprojection of raster layers, gvSIG uses the GDAL library. The reprojection process can be launched in two different ways: By activating the reprojection icon from the raster toolbar for images that have already been loaded to the view, or by reprojecting the layer before it is loaded to the view if this is needed.

The GDAL library does not support ecw, mrsid or jpeg2000 images and therefore images in these formats cannot be reprojected.

To launch the reprojection dialog from the raster toolbar, select "Geographic transformations" on the left drop-down button and "Reproject layer" on the drop-down button on the right. Make sure that the layer that you want to reproject is set as the current layer in the text box.

When launching the reprojection function from the raster toolbar, a dialog opens which shows the projection information of the input image as "source projection". The source projection cannot be changed as it is assumed that the input layer has been loaded into the view with the correct projection. Under "target projection" the projection of the output image can be set by the user through the standard gvSIG dialog for CRS and transformations. It should be noted that not all transformations are supported; the projection options depend on the GDAL reprojection library.

The output layer can be saved on disk or opened in memory as temporary file. When the first option (which is the default) is selected, the user is prompted for a file name and path. Then, the reprojection process starts and when this is finished, it will ask whether you want to add the new layer to the TOC.

NB: When reprojecting an image, the used transformation is "EPSG Transformation"; with raster layers the other transformations (manual, composed or grid) can not be used.

Images can also be reprojected before loading them to the view. To do this, you will need to have the option "Ask for projection when the raster loaded has different projection from view", located in the raster options section of the Preferences dialog, selected. If this option is selected and a raster with a different projection than the view is loaded, a dialog is opened with projection options. The default option is to load the layer while ignoring the projection, but you can reproject the layer by selecting the option "Reproject raster to the view projection". Then, the same Reprojection dialog is shown, but in this case the "target projection" is fixed to the projection of the view, and the "source projection" can be changed, as in some cases the projection of an image may not have been set correctly or the needed projection information maybe missing.

After accepting the settings, the reprojection process will start and the layer will be added to the TOC.

Alphanumeric

Exporting to dbf and xls

Exporting Tables to DBF and Excel

The application allows tables (whether layer attribute tables or separate alphanumeric tables ) to be exported in two formats:

• 1.Excel: Export data to a new Microsoft Excel file. The data appears on the second row of the first sheet. The first row contains the column names.
• 2.DBF: Export data to a dBase file.

Follow these steps to export a table:

A. Select the table:

To export a table it must first be opened. The export operations are activated once the table is opened.

To export a subset of the records use the selection tools to select the records to be exported. The records can be selected either from the attribute table or by selecting the corresponding geometries in the View.

B. Select the export option

To do this select the menu option:

For Excel: Table/Export/Excel.

For Dbase: Table/Export/DBF.

C. Enter the file name

Locate the directory where you want to create the file and type a name for the file. If the file already exists the application will ask for confirmation to overwrite it.

Joining tables

The tool for joining tables has been improved and now reflects the relationship between the tables once they have been joined. The operation of the tool remains the same in that both tables must contain a common field that will be used to join them together.

It is possible to add a prefix to the source table fields so that they can be easily identified in the joined table, e.g. Table1_FIELD1, Table1_FIELD2, etc. In a similar manner a prefix can also be added to the target table fields: Table2_FIELD1, Table2_FIELD2, etc.

The resulting joined table is given a title made up of the tables participating in the join, e.g. Table1 X Table2 X, or vice versa.

The join between the tables can be removed by selecting 'Remove joins' from the Table menu.

• Note: A layer can't be edited once a join has been established on it and the "Start Editing" option on the layer's context menu will be disabled. To start an editing session go to the Table menu and remove the existing joins.

Join

The “Join” tool allows two tables to be joined via a common field. You can also access this tool by clicking on the following button

or by going to the “Table” menu and then to “Join”. To join the two tables, carry out the following steps: Firstly, specify the source table the join is to be made from.

Then specify the field to be used for the join.

Then indicate the table you wish to join to the first one.

Finally, indicate the field in the second table which is common to the first one.

If you open the data source table, you will see that the fields of the destination table have been joined. The name of the field added to the table is identified by the word “Join_(Field name)”

Statistics

You can access this option by clicking on the following button

or by going to the “Table” menu and then to “Statistics”.

The “Statistics” tool allows you to obtain the most common statistical values.

N.B.: Remember that the tool will not be activated until you select a numerical field.

If you wish to obtain field statistics, select the field (left click on the field heading), then click on the “Statistics” tool.

You can only obtain statistics from a series of records, firstly, select the field the values are located in, then select the desired records, and click on the “Statistics” tool.