User should learn the difference between those two formats, because some modules working correctly with GRASS native data, can produce wrong results with input vector maps created by v.externa l. Limitations: Due to these data model differences v.external does not work with all data formats. In general, for all formats that do not have a key column (e.g. SHAPE file), attributes are not accessible,.
v.external.out instructs GRASS to write vector maps in external data format (e. g. ESRI Shapefile, Mapinfo, and others ) using OGR library . PostGIS data can be also written by built-in GRASS-PostGIS data provider. NOTES Number of available output formats (v.external.out -f).
External vector data can be linked via v.external using OGR library or GRASS-PostGIS data driver (format=PostgreSQL). List of supported formats can be determined by v.external-f To link file-based data formats, eg. ESRI Shapefile using OGR library v.external input=ncshape/ layer=railroads Assuming that railroads.shp is located in directory ncshape.
If you prefer not to import your vector datasets into the native GRASS vector format, you can create a virtual link to it using v .external. This can be done as follows: v .external dsn=./ output=boundary_county layer=boundary_county Building topology for vector map …
GRASS GIS: pseudo-topology and real topology. Q: What is the difference between pseudo-topology ( v .external`) and real topology? A: The differences are listed in the table below. Basically a full topological format knows what ‘network’ is so that every node is directly related with his degree of connection.
GRASS GIS Integration, GRASS GIS Integration, GRASS GIS Integration, GRASS GIS Integration, (This is not strictly true – with the GRASS modules r.external and v.external you can create read-only links to external GDAL/OGR-supported datasets without importing them. This is not the usual way for beginners to work with GRASS, therefore this functionality will not be described here.), Link selected external vector data as GRASS vector maps (using v.external ) and load them into current layer tree. Set vector output format Define external format for newly created vector maps (see v.external.out for details), 8/19/2015 · v .external: Missing – Lo v.extract: Available common, list, where v.extrude: Missing – Lo v.generalize: Available common, complicated v.hull: Available common v.import: Missing – Hi New since Community sprint in Como as a modified version of v.in.proj … About GRASS -Wiki Disclaimers …
# register GeoTIFF file to be used in current mapset: r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius # define output directory for files resulting from GRASS calculation: r.external.out directory=$HOME/gisoutput/ format=GTiff # perform GRASS calculation (here: extract pixels > 20 deg C) # this stores the output map directly as GeoTIFF: r.mapcalc warm.tif = if(modis_celsius > 20.0, modis_celsius, null() ) # cease GDAL output connection and turn back to write GRASS …
# register GeoTIFF file to be used in current mapset: r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius # define output directory for files resulting from GRASS calculation: r.external.out directory=$HOME/gisoutput/ format=GTiff # perform GRASS calculation (here: extract pixels > 20 deg C) # this stores the output map directly as GeoTIFF: r.mapcalc warm.tif = if(modis_celsius > 20.0, modis_celsius, null() ) # cease GDAL output connection and turn back to write GRASS …
QGIS, SAGA GIS, ILWIS, Marble, GDAL
