GRASS and SAGA

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Revision as of 11:41, 17 November 2009 by Jarekj 71 (talk | contribs) (3.1 Direct importing GRASS Data to SAGA (requires grass-gdal plugin))

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This tutorial is prepared to present possibilities for integration GRASS GIS with SAGA. The current version is only for linux installation.

1. Installing SAGA

Issues connected with SAGA installation presented below many occur/not occur depending on linux distribution, architecture, and gdal/ogr/proj installation.

Currently the only trustworthy installation on linux is a compilation from the source. The source can be found here The how-to install from source is described here. If we want to have direct access to GRASS data we need also to have gdal/ogr compiled from source with grass-gdal plugin correctly compiled before SAGA compilation.

It is also possible to use precompiled version of SAGA but there are problems with gdal/ogr and proj working, depending on architecture (32 or 64 bits) and gdal installation. Direct access do GRASS data also is not possible.

2. Start to work with SAGA command line on liux=

To start to work with SAGA command line on linux we need prior add access to SAGA libraries:

export SAGA_MLB=/usr/local/lib/saga

If libraries have been installed in other directory full path to that directory shall be added. If we use precompiled SAGA instalation we shall add path to saga_instalation_dir/lib. For example:

export SAGA_MLB=~/saga_gtk/lib

3. Import and Export GRASS data to SAGA and backward

3.1 Direct importing GRASS Data to SAGA (requires grass-gdal plugin)

It is possible to import grass data directly to SAGA without transitional export to GeoTIFF or other GDAL format. But this method has some limitation (some of them well known for R' spgrass6 usres):

  1. plugin can import only the whole map. It ignores both current region resolution and region boundary
  2. there are problems with NULL interpretation if we use plugin to import grass raster directly.

So we can use direct import only if raster map have no NULL values and we need both extend an map resolution. On the other hand we need to use transactional GeoTiff.

How to import: in command line we need to use following SAGA command:

saga_cmd libio_gdal 0 -GRIDS elev -FILE ~/grassdata/spearfish60/PERMANENT/cellhd/elevation.dem

where:

  • saga_cmd: command
  • cmd libio_gdal: library tu use (inpit output gdal)
  • 0: reference to read gdal
  • -GRIDS elev option name of SAGA grid file (extensions will be added by SAGA)
  • -FILE ~/grassdata/spearfish60/PERMANENT/cellhd/elevation.dem path to imported GRASS data

More about SAGA command line syntax can be found here