• The algorithm dialog
• Introduction
• The parameters tab
• The raster output tab

The algorithm dialog

Introduction

Once you double-click on the name of the algorithm that you want to execute, a dialog similar to the next one is shown (in this case, the dialog corresponds to the Anisotropic cost algorithm).

This dialog is used to set the input values that the algorithm needs to be executed. There is a main tab named Parameters where input values and configuration parameters are set. This tab has a different content depending on the requirements of the algorithm to be executed, and is created automatically based on those requirements. On the left side, the name of the parameter is shown. On the right side the value of the parameter can be set.

Those algorithms that generate raster layers as output have an additional tab named Raster output. This tab is used to set the characteristics of those output raster layers, specifying its extent and its cell size. On the lower part of the window there is a help button. Click on it to see the context help related to the current algorithm, where you will find detailed description of each parameter and each output generated by the algorithm.

The parameters tab

Although the number and type of parameters depends on the characteristics of the algorithm, the structure is similar for all of them. The parameters found on the parameters tab can be of one of the following types.

• A raster layer, to select from a list of all the ones available in the View.
• A vector layer, to select from a list of all the ones available in the View.
• A table, to select from a list of all the ones available in the View.

• A method, to choose from a selection list of possible options.
• A numerical value, to be introduced in a text box.
• A text string, to be introduced in a text box.
• A field, to choose from the attributes table of a vector layer or a single table selected in another parameter.
• A band, to select from the ones of a raster layer selected in another parameter. In both this and the previous type of parameter, the list of possible choices depends on the value selected in the parent parameter.
• A list of elements (whether raster layers, vector ones or tables), to select from the list of the ones available in gvSIG View. To make the selection, click on the small button on the left side of the corresponding row to see a dialog like the following one.

• A file or folder
• A point, to be introduced as a pair of coordinates in two text boxes (X and Y coordinates)
• A small table to be edited by the user. These are used to defined lookup tables or convolution kernels, among other parameters.

Click on the button on the right side to see the table and edit its values.

Depending on the algorithm, the number of rows can be modified or not, using the buttons on the right side of the window.

The raster output tab

The Raster output tab is found in those algorithms that generate raster layers. Unlike in most GIS, when combining several raster layers as input for an algorithm, they do not have to have the same extent an cellsize in order to process them together. That is, layers don't have necessarily to match" between them. Instead, the characteristics of the output raster layer are defined and SEXTANTE performs the corresponding resampling and cropping needed to generate layer with those characteristics.

It is responsibility of the user to enter adequate values and be aware of the limitations of this mechanism, so as to generate cartographically correct results. (i.e. you can select a small cell size for the resulting raster layers, but if the input layers you are using have a bad resolution the results will not be geographically sound).

The following options are available in the raster output tab:

• Fit to input layers. By default, the characteristics of the output raster layers are set based on the input ones. The minimum extent needed to cover all the input layers is used.
• User defined. The coordinates of the boundaries of the extent and the cellsize are both defined manually, entering the desired values in the corresponding text boxes.
• Use extent from view.. This option will let you use predefined extents from one of the views currently opened.
• Use extent from layer. The extent of a layer can be used as well to define the output characteristics, even if the layer is not used as input to the algorithm. If the selected layer is a vector one, the cellsize will have to be entered manually, since vector layers do not have an associated cellsize.

If an option other than the automatic fitting is selected, SEXTANTE will check that the values are correct and the resulting layers will not be too large (due to, for instance, a wrong cell size). If the output layers seems to large, SEXTANTE will show the next message dialog to ensure that the user really want those layer to be created.

Not all algorithms have the first option available, since not all algorithms that generate raster layers take some other raster layer as input. The interpolation algorithms, for instance, take a vector layer and create a raster one. The extent and cellsize of the latter has to be manually defined, since it cannot be set based solely on the input vector layer.