Starting grass gis2/19/2023 ![]() You can export fdr2 to fdr2.tif using r.out.gdal: r.out.gdal input=fdr2 output=fdr2. When starting GRASS GIS from a terminal console (here GRASS 8.2.0), one can continue in the GRASS terminal console, starting an interactive R session from there (here R 4.2.1). Since r.watershed uses negative integers to flag cells that receive flows from outside the computational extent by default, the above expression would have to be rewritten as follows if you want to handle both ArcGIS-derived drain and r.watershed generated drain rasters: r.mapcalc expression="fdr2=2^(8-abs(drain))" Exercise 2 - Spatio-temporal analysis of climatic data (optional) Exercise 3 - Processing climatic data from GLDAS. However, this conversion is only for those drain rasters that were converted from ArcGIS flow direction maps (positive cells only). Exercise 1 - Seasonal aggregation and statistical analysis. Now, converting drain back to fdr should be straightfoward: r.mapcalc expression="fdr2=2^(8-drain)" Convert fdr to drain: r.mapcalc expression="drain=int(8-log(fdr,2))" Start SNAP: Apps -> Desktop, choose Desktop: single application and App: GRASS GIS GRASS GIS is started automatically when the Desktop is launched.This will launch GRASS into the graphical user interface (written in wxPython). From the Welcome to GRASS GIS window, select the ncbasicspmgrass7 dataset for the location, and user1 for the mapset. In GRASS GIS, import fdr.tif first: r.in.gdal input=fdr.tif output=fdr Click on the GRASS link in the Geospatial Desktop GIS menu.In ArcGIS, right click on the flow direction layer (fdr) → Data → Export Data.Using this information, you can import the flow direction raster from ArcGIS into GRASS GIS and convert it to the drainage raster. Figure 1: ArcGIS flow direction encoding Figure 2: GRASS GIS drainage encoding Choose user1, and then try some of the GRASS modules to get a feel. You should then see the ncspm location in the left window, and the two mapsets user1 and PERMANENT in the right. East is not 0 because this module uses 0 to indicate depression areas. Start GRASS, and select the directory /home/me/grassdata as the GRASS database directory. ![]() This module measures the aspect of each cell in the counter-clockwise direction from East and divides the aspect angle by 45 so that East becomes 8, which is \(8\times 45^\circ=360^\circ\). Figure 2 shows how the r.watershed module in GRASS GIS encodes similar information in a raster map. Edit How to import ArcGIS flow direction into GRASS GISĪs shown in Figure 1, ArcGIS uses powers of two to represent the flow direction starting with \(2^0\) from East in the clockwise direction. ![]()
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