|LS| GRASS Setup =============================================================================== Using GRASS in QGIS requires you to think of the interface in a slightly different way. Remember that you're not working in QGIS directly, but working in GRASS *via* QGIS. **The goal for this lesson:** To begin a GRASS project in QGIS. |basic| |FA| Start a New GRASS Project ------------------------------------------------------------------------------- To launch GRASS from within QGIS, you need to activate it as with any other plugin. First, open a new QGIS project. * In the :guilabel:`Plugin Manager`, enable :guilabel:`GRASS` in the list: .. image:: /static/training_manual/grass/enable_grass.png :align: center The GRASS toolbar will appear: .. image:: /static/training_manual/grass/grass_toolbar.png :align: center Before you can use GRASS, you need to create a **mapset**. GRASS always works in a database environment, which means that you need to import all the data you want to use into a GRASS database. * Click on the :guilabel:`New mapset` button: |grass_new_mapset| You'll see a dialog explaining the structure of a GRASS mapset. * Create a new directory called :kbd:`grass_db` in :guilabel:`exercise_data`. * Set it as the directory that will be used by GRASS to set up its database: .. image:: /static/training_manual/grass/grass_folder.png :align: center * Click :guilabel:`Next`. GRASS needs to create a "location", which describes the maximum extents of the geographic area you'll be working in. * Call the new location :kbd:`South_Africa`: .. image:: /static/training_manual/grass/new_location.png :align: center * Click :guilabel:`Next`. * We'll be working with :kbd:`WGS 84`, so search for and select this CRS: .. image:: /static/training_manual/grass/wgs_84_selected.png :align: center * Click :guilabel:`Next`. * Now select the region :guilabel:`South Africa` from the dropdown and click :guilabel:`Set`: .. image:: /static/training_manual/grass/set_south_africa.png :align: center * Click :guilabel:`Next`. * Create a mapset, which is the map file that you'll be working with. .. image:: /static/training_manual/grass/grass_mapset.png :align: center Once you're done, you'll see a dialog asking you to confirm that the settings it displays are correct. * Click :guilabel:`Finish`. * Click :guilabel:`OK` on the success dialog. |basic| |FA| Loading Vector Data into GRASS ------------------------------------------------------------------------------- You'll now have a blank map. To load data into GRASS, you need to follow a two-step process. * Load data into QGIS as usual. Use the :kbd:`roads.shp` dataset (found under :kbd:`exercise_data/epsg4326/`) for now. * As soon as it's loaded, click on the :guilabel:`GRASS Tools` button: |grass_tools| * In the new dialog, select :guilabel:`Modules list`. * Find the vector import tool by entering the term :kbd:`v.in.ogr.qgis` in the :guilabel:`Filter` field. The :kbd:`v` stands for "vector", :kbd:`in` means its a function to import data into the GRASS database, :kbd:`ogr` is the software library used to read vector data, and :kbd:`qgis` means that the tool will look for a vector from among the vectors already loaded into QGIS. * Once you've found this tool, click on it to bring up the tool itself: .. image:: /static/training_manual/grass/grass_tool_selected.png :align: center * Set the loaded layer to :guilabel:`roads` and its GRASS version's name to :kbd:`g_roads` to prevent confusion. .. image:: /static/training_manual/grass/g_roads_selected.png :align: center .. note:: |hard| Note the extra import options provided under :guilabel:`Advanced Options`. These include the ability to add a WHERE clause for the SQL query used for importing the data. * Click :guilabel:`Run` to begin the import. * When it's done, click the :guilabel:`View output` button to see the newly imported GRASS layer in the map. * Close first the import tool (click the :guilabel:`Close` button to the immediate right of :guilabel:`View output`), then close the :guilabel:`GDAL Tools` window. * Remove the original :guilabel:`roads` layer. Now you are left with only the imported GRASS layer as displayed in your QGIS map. |basic| |FA| Loading Raster Data into GRASS ------------------------------------------------------------------------------- Recall that our DEM is in the Projected CRS :kbd:`UTM 33S / WGS 84`, but our GRASS project is in the Geographic CRS :kbd:`WGS 84`. So let's re-project the DEM first. * Load the |srtmFileName| dataset (found under :kbd:`exercise_data/raster/SRTM/`) into the QGIS map as usual, using QGIS' :guilabel:`Add Raster Layer` tool. * Re-project it using GDAL Warp tool (:menuselection:`Raster --> Projections --> Warp (Reproject)`), setting it up as shown: .. image:: /static/training_manual/grass/warp_settings.png :align: center * Save the raster under the same folder as the original, but with the file name :kbd:`DEM_WGS84.tif`. Once it appears in your map, remove the |srtmFileName| dataset from your :guilabel:`Layers list`. Now that it's reprojected, you can load it into your GRASS database. * Open the :guilabel:`GRASS Tools` dialog again. * Click on the :guilabel:`Modules List` tab. * Search for :kbd:`r.in.gdal.qgis` and double click the tool to open the tool's dialog. * Set it up so that the input layer is :guilabel:`DEM_WGS84` and the output is :kbd:`g_dem`. .. image:: /static/training_manual/grass/g_dem_settings.png :align: center * Click :guilabel:`Run`. * When the process is done, click :guilabel:`View output`. * :guilabel:`Close` the current tab, and then :guilabel:`Close` the whole dialog. .. image:: /static/training_manual/grass/g_roads_g_dem_result.png :align: center * You may now remove the original :guilabel:`DEM_WGS84` layer. |IC| ------------------------------------------------------------------------------- The GRASS workflow for ingesting data is somewhat different from the QGIS method because GRASS loads its data into a spatial database structure. However, by using QGIS as a frontend, you can make the setup of a GRASS mapset easier by using existing layers in QGIS as data sources for GRASS. |WN| ------------------------------------------------------------------------------- Now that the data is imported into GRASS, we can look at the advanced analysis operations that GRASS offers.