gvSIG-Desktop 1.10. User Manual

Once you know which data you have, it is time to know which algorithms are available and how to use them.

When you execute an algorithm using the toolbox, you use a parameters window with several fields, each one of them corresponding to a single parameter. When you use the command line interface, you must know which parameters are needed, so as to pass the right values to use to the method that runs that algorithm. Of course you do not have to memorize the requirements of all the algorithms, since SEXTANTE has a method to describe an algorithm in detail. But before we see that method, let's have a look at another one, the algs() method. It has no parameters, and it just prints a list of all the available algorithms. Here is a little part of that list as you will see it in your command-line shell.

bsh % algs();
acccost-------------------------------: Accumulated cost(isotropic)
acccostanisotropic--------------------: Accumulated cost (anisotropic)
acccostcombined-----------------------: Accumulated cost (combined)
accflow-------------------------------: Flow accumulation
acv-----------------------------------: Anisotropic coefficient of variation
addeventtheme-------------------------: Points layer from table
aggregate-----------------------------: Aggregate
aggregationindex----------------------: Aggregation index
ahp-----------------------------------: Analytical Hierarchy Process (AHP)
aspect--------------------------------: Aspect
buffer--------------------------------: Buffer

On the right you find the name of the algorithm in the current language, which is the same name that identifies the algorithm in the toolbox. However, this name is not constant, since it depends on the current language, and thus cannot be used to call the algorithm. Instead, a command-line is needed. On the left side of the list you will find the command-line name of each algorithm. This is the one you have to use to make a reference to the algorithm you want to use.

Now, let's see how to get a list of the parameters that an algorithms require and the outputs that it will generate. To do it, you can use the describealg(name of the algorithm) method. Use the command-line name of the algorithm, not the full descriptive name.

For example, if we want to calculate a ow accumulation layer from a DEM, we will need to execute the corresponding module, which, according to the list show using the ags() method,is identified as accflow. The following is a description of its inputs and outputs.

>describealg("accflow")
Usage: accflow(DEM[Raster Layer]
              WEIGHTS[Optional Raster Layer]
              METHOD[Selection]
              CONVERGENCE[Numerical Value]
              FLOWACC [output raster layer])