- Raster
- Adding a layer from a disk file
- Adding a layer using the WMS protocol
- Connecting to the service
- Accessing the service
- Selecting 'Layers'
- Selecting 'Styles' for the WMS server layers
- Selecting values for a WMS layer's 'Dimensions'
- Selecting the format, spatial system and/or transparency
- Adding the layer to the view
- Modifying the layer's properties
- Adding a layer using the WCS protocol
- Accessing the service
- Selecting 'Coverages'
- Selecting the 'Format'
- Adding the layer to the view
- Modifying the layer's properties
- Adding orthophotos using the ECWP protocol
- Adding a layer using the ArcIMS raster
- Introduction to ArcIMS
- Connecting to image services
- Adding a layer using the ArcIMS protocol
- Add layer using the arcIMS protocol
- Connecting to the server
- Accessing the service
- Selecting layers
- Adding the layer to the view
- Points to remember about spatial reference systems
- Modifying the layer's properties
- Information about scale limits
- Attribute information requests
- Connecting to geometry services
- Adding a geometry layer
- ArcIMS symbols
- Symbols
- Legends
- Working with the layer
- Web Map Context
Raster
Adding a layer from a disk file
Click on the "Add" button
The "Add” dialogue window allows you to move around the file system to select the layer to be loaded. Remember that only the files of the type selected will be shown. To indicate the type of file to be loaded, select a file from the “Files of type” pull down menu.
If several layers are loaded at the same time, the order in which the themes will be added to the view can be specified with the "Up" and "Down" buttons in the “Add layer" dialogue.
Adding a layer using the WMS protocol
Go to the "Add layer" window and then select the WMS tab.
- The pull-down menu shows a list of WMS servers (you can add a different server if you don’t find the one you want).
- Click on “Connect”.
- and 4. When the connection is made, a welcome message from the server appears, if this has been configured. If no welcome message appears, you can check whether you have successfully connected to the server if the “Next” button is enabled.
- The WMS version number that the connection has been made to is shown at the bottom of the box.
Click on “Next” to start configuring the new WMS layer.
When you have accessed the service, a new group of tabs appears.
The first tab in the adding a WMS layer wizard is the information tab. It summarises the current configuration of the WMS request (service information, formats, spatial systems, layers which make up the request, etc.). This tab is updated as the properties of its request are changed, added or deleted.
The wizard’s “Layers” tab shows the WMS server’s table of contents.
Select the layers you wish to add to your gvSIG view and click on “Add”. If you wish, you can choose a name for the layer in the “Layer name” field.
N.B. Several layers can be selected at the same time by holding down the “Control” key and left clicking on the mouse.
N.B. To obtain a layer description move the cursor over a layer and wait a few seconds. The information the server has about these layers is shown.
The “Styles” tab allows you to choose a display view for the selected layers. However, this is an optional property and the tab may be disabled because the server does not define styles for the selected layers.
The “Dimensions” tab helps to configure the value for the WMS layer dimensions. However, the dimensions property (like the styles property) is optional and may be disabled if the server does not specify dimensions for the selected layers.
No dimension is configured by default. To add a dimension, select one from the “Settings editor” area in the list of dimensions. The controls in the bottom right-hand corner of the tab are enabled. Use the slider control to move through the list of values the server has defined for the selected dimension (for example “TIME” refers to the dates the different images were taken). You can move back to the beginning, one step back, one step forward or move to the end of the list using the navigation buttons which are located below the slider control. If you know the position of the value you require, you can simply write it in the text field and it will move automatically to this value.
Click on “Add” so that you can write the selected value in the text field and request it from the server.
gvSIG allows you to choose between:
Single value: Only one value is selected
Multiple value: The values will be added to the list in the order they are selected in
Interval: An initial value and then an end value are selected
When the expression for your dimension is complete, click on “Set” and the expression will appear in the information panel.
N.B. Although each layer can define its own dimensions, only one choice of value is permitted (single, multiple or interval) for each variable (e.g. for the TIME variable a different image date value cannot be chosen in each layer).
N.B. The server may come into conflict with the layer combination and the variable value you have chosen. Some of the layers you have chosen may not support your selected value. If this occurs, a server error message will appear.
N.B. You can personalise the expression in the text field. The dialogue box controls are only designed to make it easier to edit dimension expressions. If you wish you can edit the text field at any time.
The “Formats” tab allows you to choose the image format the request will be made with, specify if you wish the server to hand in the image with a transparency (to superimpose the layer onto other layers the gvSIG view already contains) and also the spatial reference system (SRS) you require.
As soon as the configuration is sufficient to place the request, the “Ok” button is enabled. If you click on this button, the new WMS layer will be added to the gvSIG view.
Once the layer has been added its properties can be modified. To do so, go to the Table of contents in your gvSIG view and right click on the WMS layer you wish to modify. The contextual menu of layer operations appears. Select “WMS Properties”. The “Config WMS layer” dialogue window appears. This is similar to the wizard for creating the WMS layer and can be used to modify its configurations.
Adding a layer using the WCS protocol
Click on “Next” to start configuring the new WCS layer.
When you have accessed the service, a new group of tabs appears.
The first tab in the adding a WCS layer wizard is the information tab. It summarises the current configuration of the WCS request (service information, formats, spatial systems, layers which make up the request, etc.). This tab is updated as the properties of its request are changed, added or deleted.
Select the coverage you wish to add to your gvSIG view. If you wish, you can choose a name for your layer in the “Coverage name” field.
You can choose the image format you wish to use to make the request and reference system (SRS) in the “Format” tab.
N.B. Tabs such as “Time” and “Parameters” are disabled in this case. Configuring these variables depends on the server chosen and the type of data it has access to.
As soon as the configuration is sufficient to place the request, the “Ok” button is enabled. If you click on this button, the new WCS layer will be added to the gvSIG view.
Once the layer has been added its properties can be modified. To do so, go to the Table of contents in your gvSIG view and right click on the WCS layer you wish to modify. The contextual menu of layer operations appears. Select “WCS Properties”.
The “Config WCS layer” dialogue window appears. This is similar to the wizard for creating the WMS layer and can be used to modify your configurations.
Adding orthophotos using the ECWP protocol
If you wish to add an orthophoto to gvSIG using the ECWP protocol, first open a view and click on the “Add layer” button.
Click on the “Add” button in the dialogue box. A file browser window appears.
Choose the “gvSIG Image Driver” option from the “Files of type” pull-down menu.
Write the URL of the file you wish to load as follows in “File name”:
ecwp://server address/path of the file you wish to add.
For example:
ecwp://raster.alava.net/datos/ecw/Ortofoto_5000.ecw
ecwp://earthetc.com/images/geodetic/world/MOD09A1.interpol.cyl.retouched.topo.bathymetry.ecw
When you have input the data, click on “Open”.
The orthophoto will be added to the layer list.
Select the new added layer and click on “Ok”.
The image will be added to the view.
Adding a layer using the ArcIMS raster
In the proprietary software environment, ArcIMS (developed by Environmental Sciences Research Systems, ESRI) is probably the most widespread/popular widely used (Internet) cartographic server on the Internet thanks to the number of clients it supports (HTML, Java, ActiveX controls, ColdFusion...) and to its integration with other ESRI products. ArcIMS is currently one of the most important remote cartographic information providers. Although the protocol it uses does not comply with the Open Geospatial Consortium (because it was created long beforehand), the gvSIG team believes that offering support for ArcIMS is important.
The extension can access image services offered by an ArcIMS server. This means that, just like a WMS server, gvSIG can request a series of layers from a remote server and receive a view rendered by the server containing the requested layers in a specific coordinate system (reprojecting if necessary) and in specific dimensions. In addition to displaying geographic information, the extension allows you to request information about the layers for a particular point via the gvSIG standard information button.
ArcIMS is slightly different in its philosophy from WMS. In WMS, the request is normally made by independent layers whilst in ArcIMS the request is global.
The steps required to request a layer from an ArcIMS server and to request information for a particular point are listed below.
Our example uses the ESRI ArcIMS server. Its URL is http://www.geographynetwork.com. This is the address a web browser requires to access the HTML visual display unit.
Before loading a layer from this server, the datum WGS84 in geodesic coordinates (code 4326) has to be set up previously as the view’s spatial system.
If the extension is loaded correctly, a new ArcIMS data source will appear in the “Add layer” dialogue box.
Adding a new layer to the view
If the server has a standard configuration, simply indicate its address. gvSIG will try to find the servlet’s full address.1 If the servlet has a different path, you will have to write it into the dialogue box.
When the connection has successfully been made, the server version, its compilation number and a list of image and geometry services available are shown.
The service can be selected from the list or can be written in directly.
Finally, if the “Override service list” check box is enabled, gvSIG will delete any catalogue that has already been downloaded and will request them again from the server.
List of services available
The next step is to select the ImageServer type service required by double clicking or selecting it and clicking on "Next". The dialogue box changes and an interface with two tabs appears (fig. 3). The first tab shows the metainformation given by the server about the service’s geographic limits, the acronym of the language it has been written in, units of measurement, etc. It is a good idea to find out if a coordinate system has been defined in the service (using EPSG codes) as this can directly influence the requests made to the server, as Figure 3 shows.
N.B. If no coordinate system has been defined in the service, the extension will assume that it is the same coordinate system as the one we have defined for the view.
Figure 3: Metadata from the ArcIMS server
We can continue by clicking on "Next" or return to the previous dialogue by clicking on "Change service”.
The last dialogue box is the layer selection. We can define a name for the gvSIG layer or leave the default value (the service name) in this window. A box appears below with a list of the service layers in tree form. When the mouse is moved over the layers, information about these layers appears: extension, scale ranges, type of layer (raster or vector image) and if it is visible by default in the service (fig. 4).
Figure 4: Metadata from a service layer
We can view each layer’s ID via the “Show layer ID” check box. This check box is useful when there are layers whose descriptor is repeated. Therefore, the only way to distinguish between them is via an ID, which will always be unique. A combo box is also available to select the image format we wish to use to download the images. We can choose JPG format if our service works with raster images or one of the other remaining formats if we want the service to have a transparent background.
N.B. The transparency in 24-bit PNG images is not correctly displayed in gvSIG 0.6. This type of files will be supported in gvSIG 1.0.
The box with the layers selected for the service appears below. If you wish, you can add just some of the service layers and also reorganise them. This makes the service view totally personalised.
N.B. The configuration cannot be accepted until a layer has been added.
N.B. Multiple selections of service layers can be made by using the Control and CAPS keys.
When the “Ok” button in the dialogue box is pressed, a new layer appears in the view (fig. 5). If no layer has been added previously, the extension of the ArcIMS layer is shown, as per the standard gvSIG procedure.
Figure 5: ArcIMS layer added to the gvSIG view.
It must be remembered that when the layer extension is shown, the layers that make up the chosen configuration may not appear and a blank or transparent image appears instead. If this occurs, use the scale control dialogue box (V. Information about scale limits section).
An ArcIMS server does not define the spatial reference systems it supports as opposed to the WMS specification. This means that a priori we do not have a list of EPSG codes that the map server can reproject. In short, ArcIMS can reproject to any coordinate system and leaves the responsibility of how the projections are used to the client.
Therefore, if our gvSIG view is defined in ED50 UTM zone 30 (EPSG:23030) and we request a global coverage service (stored for example in the geographic coordinates WGS84, which correspond to code 4326) the server will not be able to reproject the data correctly because we are using global coverage for a projection of a specific area of the Earth.
However, the procedure can be carried out in reverse. If we have a view in geographic coordinates (and thus global coverage), services defined in any coordinate system can be requested because the server will be able to transform the coordinates correctly.
In short, requests to the ArcIMS server must be made in the view's coordinate system and they cannot be requested in another coordinated system.
Moreover, as we mentioned above, if an ArcIMS server does not offer information about the coordinate system its data is in, the user will be responsible for setting up the correct coordinate system in the gvSIG view. Thus, if a user with a view in UTM adds a layer which is in geographic coordinates (even though the server does not show it), the service will be added correctly but will take the view to the geographic coordinates domain (in sexagesimal degrees).
An additional effect is that if the view uses different units of measurement from the server, the scale will not be shown correctly.
The layers requested from the server can be modified via a dialogue box, which can be accessed from the layer’s contextual menu (fig. 6) just like the WMS layers. This dialogue box is similar to the box used to load the layer, apart from the fact that the service cannot be changed.
Figure 6: Properties of the ArcIMS layer
The extension allows us to consult the layers' scale limits which make up the requested service via a dialogue box which can be maintained in the view during the session (fig. 7). This window shows the layers on the vertical axis and the different scale denominators on the horizontal axis via a logarithmic scale. This box is small on screen but can be enlarged to improve the difference between the scales.
The vector layers, raster layers and the layers that can be seen on the current scale (marked with a vertical line) in a darker colour and the layers we cannot see above or below the current scale are differentiated by different coloured bars (described in the window legend).
Figure 7: Scale limits status
Attribute information requests about the elements for a particular point is one of gvSIG’s standard tools. Its functionality is also supported by the extension.
The WMS specification allows information about several layers to be requested from the server in one single query. This is different in ArcIMS. We need to make one server request per layer required.
This means that no requests for unloaded layers or unseen layers that are not visible on the current scale or layers whose extension is outside the view will be made. Even if all these layers are filtered, the information request usually takes longer than is desirable because of this intrinsic feature of ArcIMS.
When all the request responses have been recovered, the standard gvSIG attribute information dialogue appears with each of the layers (LAYER) which return information as a tree. If we click on a layer, its name and ID appear on the right (fig. 8).
Under this node, if we are talking about a vector layer, all the records or geometric elements the server has responded to appear, and give each one their corresponding attributes (FIELDS).
If it is a raster layer, such as an orthoimage or a digital terrain model, it returns the values for each of the bands (BAND) in the requested pixel colour, instead of records.
Figure 8: Displaying attribute information
The extension allows access to both ArcIMS image services and geometry services (Feature Services). This means that a server can be connected to and geometric entities (points, lines and polygons) and their attributes obtained. This is not dissimilar to WFS service access.
However, the variety of existing geometry services is much lower than the variety in the image server. There are two main reasons for this. On one hand, providing the public with vector cartography implies security problems because many bodies only want to offer the general public views and images. The vector data becomes either an internal product or must be paid for. On the other hand, this type of services generate much more traffic on the network and in the case of basic information servers could become a problem.
Loading a geometry layer is practically the same procedure as loading the image server as mentioned above (Accessing the service section and the following sections). In this case, the number of layers to be selected must be taken into account. If we wish to download all the layers offered by the service the response time will be very high.
The only difference between loading an image layer is that in this case we can choose whether we wish the layers to be downloaded as a group via a check box. This is useful for processing the vector layers as one layer when it needs to be moved and activated in the table of contents.
Unlike the image service, in which all the service’s layers appear as one unique layer in the gvSIG view, in this case each layer is downloaded separately and appears in the view grouped under the name defined in the connection dialogue.
Cartography symbols are configured in the server in one AXL extension file for both geometry and image services. We can divide symbol definition into two parts. On one hand, we can talk about the definition of the symbols themselves, i.e. how a geometric element, such as a line or polygon, should be presented. On the other hand, we can talk about the distribution of these symbols according to the cartographic display scale or to a specific theme attribute.
In ArcIMS terminology symbols are different from legends (SYMBOLS and RENDERERS).
There are various types of symbols: raster fill symbols, gradient fill symbols, simple line symbol, etc. The extension adapts the majority of the symbols generated by ArcIMS. Table 1 shows the ArcIMS symbols and indicates whether they are supported by gvSIG.
| Label | Description | Supported |
|---|---|---|
| CALLOUTMARKERSYMBOL | Balloon-type label | NO |
| CHARTSYMBOL | Pie chart symbol | NO |
| GRADIENTFILLSYMBOL | Fill in with gradient | NO |
| RASTERFILLSYMBOL | Fill with raster pattern | YES |
| RASTERMARKERSYMBOL | Point symbol using pictogram | YES |
| RASTERSHIELDSYMBOL | Customised point symbol for US roads | NO |
| SIMPLELINESYMBOL | Simple line | YES |
| SIMPLEMARKERSYMBOL | Point | YES |
| SIMPLEPOLYGONSYMBOL | Polygon | YES |
| SHIELDSYMBOL | Point symbol for US roads | NO |
| TEXTMARKERSYMBOL | Static text symbol | NO |
| TEXTSYMBOL | Static text symbol | YES |
| TRUETYPEMARKERSYMBOL | Symbol using TrueType font character | NO |
Table 1: ArcXML symbol definition labels
In general, the most common symbols have been successfully “transferred”. Some of the symbols cannot be obtained directly from gvSIG (at least in the current version), such as the raster fill symbol or they need to be “adjusted” such as the different types of lines. This means that a raster fill symbol is not a symbol that can be defined by the gvSIG user interface, but it can be defined by programming.
gvSIG supports the most common types of legends: unique value and range and value themes as well as the scale-range control over the whole layer. ArcIMS goes much further in its configuration. It can generate much more complicated legends in which symbols can be grouped together, scale-range controls can be established for labels and symbols and different labelling based on an attribute can be shown (as though it were a value theme for labelling).
This group of legends can generate very complex symbols for a layer in the end. The current implementation status of the gvSIG symbols needs to be simplified to reach a compromise to recover the symbols that best represent the layer as a whole.
| Label | Description |
|---|---|
| GROUPRENDERER | Legend which groups others together |
| SCALEDEPENDENTRENDERER | Scale dependent legend |
| SIMPLELABELRENDERER | Labelling layer legend |
| SIMPLERENDERER | Unique value layer legend |
| VALUEMAPRENDERER | Value and range themes |
| VALUEMAPLABELRENDERER | Labelling themes |
Table 2: ArcXML legend definition labels
When a GROUPRENDERER is found, the symbol ArcIMS draws first is always chosen. Thus, in the case of the typical motorway symbol for which a thick red line is drawn and a thinner yellow line is drawn over it, gvSIG will only show the red line with its specific thickness.
If a scale dependent legend is discovered during a symbol analysis, this is always chosen. If more than one is discovered, the one with the greatest detail is chosen. For example, in ArcIMS we can have a layer with simple road symbols (only main roads are drawn) on a 1:250000 scale and based on this a different theme is shown with all types of roads (paths, tracks, roads, etc.). In this case, gvSIG will show this last theme as it is the most detailed.
If a labelling legend is discovered during a symbol analysis, it will be saved in a different place and will be assigned to the selected definitive legend. In the case of the VALUEMAPLABELRENDERER label, only the legend of the first processed value will be obtained as a label symbol. The rest will be rejected.
In short, it is obvious that the failure to adapt the legends for gvSIG is a simplification process in which different legend and symbol definitions must be rejected to obtain a legend which is similar to the original as far as possible. It is to be expected that the gvSIG symbol definition will improve considerably so that it can support a larger group of cases in the future.
Working with the layer is similar to any other vector layer, as long as we remember that access times may be relatively high. The layer attribute table can be consulted, in which case the records will be downloaded successively as we display them.
If we wish to change the table symbols to show a unique value or range theme we must wait as gvSIG requests the complete table for these operations. On the other hand, the downloading of attributes is only carried out once per layer and session and therefore, this wait only occurs in the first operation.
In general, if our ArcIMS server is in an Intranet, it will be relatively fast to handle, but if we wish to access remote services we may be faced with considerable response times.
The main feature to bear in mind when working with an ArcIMS vector layer is that the geometries available at any given time are only the ones displayed. This is because we can connect to huge layers but only the visible geometries are downloaded. As far as gvSIG is concerned, the geometries shown on the screen are the only ones available and thus, if we export the view to a shapefile for example, are only a part of the layer.
Finally, we need to remember that to speed up the geometry downloads they are simplified to the viewing scale in use at any given time. This drastically reduces the amount of information downloaded as only the geometries that can actually be "drawn" are displayed in the view.
Loading a geometry layer is practically the same procedure as loading the image server as mentioned above (Accessing the service section and the following sections). In this case, the number of layers to be selected must be taken into account. If we wish to download all the layers offered by the service the response time will be very high.
Unlike the image service, in which all the service’s layers appear as one unique layer in the gvSIG view, in this case each layer is downloaded separately and appear in the view grouped under the name defined in the connection dialogue.
After a few seconds the layers appear individually but are grouped under a layer with the name we have defined for it.
The layer symbols are established at random. A pending feature is to recover the service symbols and configure them by default so that gvSIG can display the cartography as similarly as possible to how it was established by the service administrator.
Web Map Context
Web Map Context (WMC) is another OGC standard (http://www.opengeospatial.org) which can be added to the list of standards of this type supported by gvSIG.
It can reproduce a view made up of Web Map Services (WMS) layers on any GIS platform which supports WMC. If your project has a view which contains WMS layers, you can export these layers. The result is an XML file with a specific format and .cml extension which can be imported by another platform on which the view it describes can be reproduced.
Web Map Context (WMC) is another OGC standard (http://www.opengeospatial.org) which can be added to the list of standards of this type supported by gvSIG.
It can reproduce a view made up of Web Map Services (WMS) layers on any GIS platform which supports WMC.
If your project has a view which contains WMS layers, you can export these layers. The result is an XML file with a specific format and .cml extension which can be imported by another platform on which the view it describes can be reproduced.
Exporting a view to WMC
Exports to WMC are currently limited to WMS type layers, although it is hoped that its functions will extend to all layers that comply with OGC standards in the future.
To obtain a WMC file, open a view in gvSIG and add the WMS layers you require.
Then go to the “View” menu and select “Export” and then “Web Map Context”.
The following dialogue will be shown.
N.B.: If you cannot find the "Web Map Context" option in the "Export" option, your project does not contain any WMS layers.
Basic mode only shows the compulsory properties which cannot be taken for granted by the application.
View: This defines which view is going to be exported to the WMC. The view which is currently active is selected by default.
Title: This is the title of the view which will be shown when your .cml file is loaded at a later date. The current title of the view is used by default but this can be changed.
ID: This field is also compulsory and represents a file ID which must be unique.
File: You can search for the place you wish to save the .cml file in from the "Browse" button.
Version: Use this tool to specify the WMC version you wish to use.
The version 1.1.0 is selected by default as it is the most highly developed and the most recommended. However, several applications and geoportals are often limited to a specific version.
gvSIG currently supports Web Map Context in its versions 0.1.4, 1.0.0 and 1.1.0.
Extent: This defines the extension of the map to be exported.
Defined by the view’s extent. This option only exports what we can currently see in the view.
Use full extent. This extension is better to use the full WMS layers depending on how their respective servers define them.
If you click on the “Advanced” button, the advanced configuration dialogue will drop down. This allows you to define more properties to obtain a complete WMC.
Abstract: This contains a summary of the view defined by WMC.
Keywords: This list of words allows you to classify and “metadata” the WMC.
URL description: If you have a web site which refers to this WMC, write its link here.
URL logo: If you have an image associated with this WMC, write its link here.
Map size (pixels): This defines the pixel size that the WMC-defined view will have. The current gvSIG view size is used by default but you can customise the size if you wish.
Contact info: Information that allows third parties to contact the WMC author.
Importing Web Map Context allows you to use gvSIG to open views with WMS layers which have been created with other platforms or with another gvSIG.
Use the "View” menu and select “Import” and then “Web Map Context”.
The WMC file selection dialogue opens.
Choose the WMC file you wish to import. On the right, you can specify how you wish to view the layers.
New view: This adds a new view to the current project and loads the WMC as specified in the file.
Layers in the active (current) view: This option only appears if the active gvSIG window is a view. It allows you to quickly add the layers to the current view.
Layers in other view: This adds the layers defined by the WMC in the chosen view. In this option, a list of views appears to select the view that will contain the new layers.
Click on the “Open” button to import the file based on your preferences.
