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115 lines
4.4 KiB
Plaintext
115 lines
4.4 KiB
Plaintext
A short guide for creating and editing GRASS GIS 7 algorithms:
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Each GRASS command, to be executed from a processing framework element such as the toolbox
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or the graphical modeler, needs to be described to let it know the inputs
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required by the commands, the output it generates and the parameters that are
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used to configure it. Each command is described in a separate text file, although
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some commands might be split in several algorithms, needing thus several files
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and adding more than one new entry to the algorithms list. Splitting
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a grass command is usually done because the processing framework does not support optional
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parameters, so it will call GRASS using all parameters defined in the description
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file.
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Here is an explanation of the content of these descriptions files, so you can
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create you own ones or edit current ones to improve them.
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Each file starts with three lines containing:
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- The name of the grass command to call to execute the algorithm (e.g. v.buffer)
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- The name of the algorithm to show to the user. This is usually the same as the
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GRASS command, but it can be different
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- The name of the group where you want the command to appear
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After this three lines, a variable number of lines appear, describing all inputs
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and ouputs. Here is a brief explanation of the format of these lines, depending
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on the type of parameter or output to be described. All declarations are contained
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in a single line, with elements separated by the symbol "|"
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- A raster layer
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ParameterRaster|base|base|False
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ParameterRaster|[name of GRASS parameter]|[description of parameter to show]|True/False, indicating if the parameter is optional or not
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Example: ParameterRaster|base|base|False
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- A vector layer
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ParameterVector|[name of GRASS parameter]|[description of parameter to shown]|[A number indicating the type of geometry]|True/False, indicating if the parameter is optional or not
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ParameterVector|input|Name of input vector map|-1|False
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To indicate the type of geometry, use the following values:
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-1: any geometry
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0: points
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1: lines
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2: polygons
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- A numerical value
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ParameterNumericalValue|[name of GRASS parameter]|[description of parameter to show]|[min value]|[max value]|[default value]
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"None" can be used for both min and max values to indicate that there is no lower
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or upper limit.
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If the default value is written as a real number (i.e. it contains a decimal
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point, even if it is an integer value like 4.0), the parameter can take any value,
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including decimal ones. If it is written as an integer (i.e. 4), the parameter is
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assumed to accept only integer values
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Example: ParameterNumber|levels|levels|1|256|32
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- A string
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ParameterString|[name of GRASS parameter]|[description of parameter to show]|[default value]
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- A value to select from a list
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ParameterSelection|[name of GRASS parameter]|[description of parameter to show]|[list of possible values, separated by semicolons]|[zero-based index of default value]
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- A boolean value
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Example: ParameterBoolean|-c|-c|True
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- Outputs
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All outputs are added with the following syntax:
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[type of output]|[name of GRASS output]|[description of output to show]
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The following types are available
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-OutputRaster
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-OutputVector
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-OutputTable
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-OutputFile (for any file that is not a layer or table of a format supported by QGIS)
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- Advanced parameters
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to tag a parameter as "advanced", just add "*" before its declaration. For instance:
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*ParameterBoolean|-c|-c|True
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ADVANCED OUTPUT PROCESSING
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--------------------------
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In some cases, it might be interesting to take the console output from GRASS and
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extract a part of it for saving or formatting.
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Two things can be done about this:
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- Creating an HTML file with output. Just add an output of type OutputHTML.
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It's value will not be passed to GRASS, but you can use it later to create the
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HTML file from the console output. You should create a python file in the
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grass/ext package, with the same name as the grass module, with dots replaced
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by low hyphens (for instance r_quantile.py for the r.quantile command), and
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add a postProcessResults(alg) method. It will be called when the execution of
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the GRASS command is finished.
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- Creating a text file. Do as above, but adding an output of type OutputFile.
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Since some GRASS commands might use this type of output, and to make sure that
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the value of this output is not passed to the GRASS command when calling it,
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the output has to be named 'outputtext'
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