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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"><title>GRASS-SEXTANTE</title></head><body> |
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<h2>Configuring and using GRASS from SEXTANTE.</h2> |
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<br>
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This documents describes how to configure SEXTANTE so it can call GRASS |
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algorithms and incorporate them into its own set of geoalgorithms.
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It also gives some additional information on the mechanism used by |
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SEXTANTE to integrate GRASS functions, which should be useful for all |
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users, but specially for those familiar with the GRASS command-line |
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interface.<br>
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<br>
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Configuring SEXTANTE to use GRASS takes just a few easy steps. Once you |
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have configured the system, you will be able to execute GRASS |
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algorithms from any SEXTANTE component like the toolbox or the |
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graphical modeller, just like you do with any other SEXTANTE |
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geoalgorithm.<br>
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<br>
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Open the settings dialog and select the GRASS menu. You will see something like this:<br>
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<br>
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<img style="width: 605px; height: 501px;" alt="" src="grass_conf_en.png"><br> |
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<br>
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Only two parameters must be set, namely:<br>
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<br>
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<ul>
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<li>
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The path to the grass installation folder. Needed by SEXTANTE to
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execute GRASS commands. Under Linux, this is usually usr/lib/grassXX<br>
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</li>
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<li>
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The path to a GRASS mapset. The mapset doesn't have to contain any data |
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at all, since data will be imported automatically each time you execute |
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an algorithm. The only important part of the mapset is the location |
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information, particularly the Coordinate Reference System. You must set |
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the same CRS that is used by the layers that you want to process using |
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GRASS algorithms. If, for instance, you have layers with data in the |
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EPSG 23030 reference system, you must set the mapset to that same |
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reference system. When data is imported into the mapset, no |
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reprojection is performed, and layers are assumed to be in the same |
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projection as the mapset itself.</li>
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</ul>
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<br>
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Once you have set the previous paths, click on OK to close the settings |
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dialog. SEXTANTE will now try to execute GRASS and create the |
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definition files that are used to generate the graphical interfaces of |
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all the suitable GRASS algorithms, along with the corresponding help |
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files. This process might take a few seconds. If you are running |
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Windows, you will see a new window (by default it is minimized). Just |
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wait until it closes. After that, GRASS |
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algorithms will be shown in the toolbox and identified with a GRASS |
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icon. They will appear in a new branch named "GRASS" in the algorithms |
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tree -which contains two groups: raster (r.*) and vector (v.*)-, and |
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also in the usual groups used for built-in SEXTANTE algorithms. This |
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way, it is easier to find the right algorithm, both for SEXTANTE users |
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with no previous GRASS experience and former GRASS users.<br>
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<br>
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Not all GRASS algorithms are available from SEXTANTE. Some of them are |
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not compatible with the architecture of SEXTANTE and its |
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algorithm-definition semantics, while others do not make much sense in |
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the context of SEXTANTE (like, for instance, those used to digitize and |
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create new vector layer). Unsuitable algorithms are automatically |
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removed and will not appear in any SEXTANTE component.<br>
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<br>
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<h2>How the SEXTANTE-GRASS integration works. Limitations and other issues.</h2> |
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<br>
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If you are a GRASS user, it might be useful for you to know how |
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SEXTANTE calls GRASS algorithms and comunicates with the GRASS |
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interface. This can be summarized in the following steps:<br>
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<br>
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<ul>
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<li>Importing data. The layers that have been selected as input are
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imported into the GRASS mapset. Not every layer that you can open in |
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your GIS can be used to execute a GRASS algorithm. It must be a |
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file-based layer and it must have a format compatible with the |
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capabilities of the GRASS modules that import external data. Refer to |
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the GRASS help files for further information.</li>
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<li>Processing. The selected GRASS algorithm is executed.</li> |
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<li>Exporting results. Resulting data are exported to the filenames
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selected by the user in the input parameters dialog. Only layers |
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(whether raster or vector) are exported. Any other results that might |
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have been created by the algorithm (such as, for instance, text results |
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shown in the console window) are not handled, and therefore, they will |
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not be presented as results by the wrapping SEXTANTE algorithm. Also, |
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take into account that exporting data also has its limitations, and not |
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all the information generated might be available. For instance, |
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topological information will be lost, since data are exported to |
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shapefile format, which cannot store it. for further details, check the |
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help file associated with GRASS export modules.</li>
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</ul>
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<br>
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All this steps are stored in a batch file that is executed using the |
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GRASS_BATCH_JOB variable. When SEXTANTE invokes GRASS, the
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commands in the batch file are executed and GRASS closes up |
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automatically after that.<br>
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