Tips for Arc users

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If you wish to use both GRASS GIS and ArcGIS together, this page is for you.

Working with your ArcGIS data

Importing ArcGIS Data

GRASS GIS provides converters for importing ESRI shapefiles, e00 files, and many other GIS formats as well. The key GRASS modules for importing vector formats are v.in.ogr (for ESRI Shapefiles, MapInfo files, SDTS, TIGER, etc.) and v.in.e00 for e00 format. For raster data, there is r.in.gdal.

Coordinate Reference Systems

The GRASS data structure requires that each data layer have its CRS exactly defined. This is done by maintaining data layers within a "Location". Each Location has a strictly defined projection, and datum, and all the data layers (raster and vector) within that location should already be either created in or projected to that CRS. GRASS does not do "on-the-fly" reprojection to avoid often encountered in other GIS software with datum mismatches. Consequently, data layers in one location are not visible from other locations. However, GRASS does supply a collection of tools for projecting vector and raster layers from one location to another. Use of these tools is explained in the projectionintro.

Vector import/export

  • v.in.ogr - Convert OGR supported vector formats to GRASS vector format.
  • v.out.ogr - Convert from the GRASS vector format to one of the supported OGR vector formats.
  • v.in.e00 - Import a E00 coverage into a GRASS vector map.

Import of Shapefiles into GRASS

specify the directory

v.in.ogr dsn=/home/data/navigation_files output=Tracklines layer=Ship_Tracklines
or just the .shp file name directly
v.in.ogr dsn=Ship_Tracklines.shp output=Tracklines

This is the syntax for v.in.ogr in its most basic form. The dsn parameter corresponds to the directory path of the vector you are trying to import. You can enter a full or relative path. The output paramter, aptly enough, is the name of your output Grass vector. The layer parameter is the name of the input vector, be it shapefile, MapInfo file, or what have you.

Export of Shapefiles from GRASS

Shapefiles can only hold one type of data (point, line, polygon) per shapefile. You can't export a GRASS vector map with both points and areas to a single shapefile. You'll have to do it in two passes to two different files with v.out.ogr and different "type=" parameters.

Export lines from GRASS vector map to Shapefile format (generates /tmp/testogr.shp and related files):

v.out.ogr input=multi type=line dsn=/tmp olayer=testogr 

Export areas from GRASS vector map to Shapefile format (generates /tmp/testogr.shp and related files):

v.out.ogr input=multi type=area dsn=/tmp olayer=testogr 

Export 3D lines from GRASS vector map to Shapefile format:

v.out.ogr input=lines_3d type=line dsn=/tmp olayer=testogr lco="SHPT=ARCZ"

Various vector operations

  • Editar diferencias
Tips para la digitalización de áreas con atributos

Importación/exportación de rásters

  • r.in.gdal - Importa archivos ráster a un soportados por GDAL a una capa de mapa ráster binaria.
    • Importar una malla binaria ArcInfo a GRASS:
      • Ver la página de GDAL para AIC
      • Usualmente el archivo .adf más grande es el que se debe importar -- revise los valores de sus datos luego de realizar la importación aun cuando sean visualmente correctos.
r.in.gdal input=/path/to/map/hdr.adf output=map
  • r.out.gdal - Exporta datos ráster a varios formatos.
    • Exportar un ráster como un GeoTIFF para usarlo en ArcView 3.1:
r.out.gdal input=map output=map.tif type=Byte createopt="INTERLEAVE=PIXEL,COMPRESS=PACKBITS"

Importar malla ráster ArcASCII y conectar a la base de datos

El truco está en convertir la cobertura ráster a áreaas vectoriales para sacar ventaja del manejo atributos/bases de datos de los vectoriales en GRASS. Puede usar el comando r.in.gdal para importar.

# importar malla  ArcASCII a una localización UTM55S
r.in.gdal  input=aas_z55.asc output=aas_z55
r.colors aas_z55.gdal color=random
r.info aas_z55

# convertir a áreas vectoriales, usando los valores del ráster como categorías
g.region rast=aas_z55
r.to.vect -v in=aas_z55.gdal out=aas_z55 feature=area

# deshacerse de la tabla vacía creada
v.db.droptable aas_z55

# copiar la tabla real al directorio $MAPSET/dbf/
eval `g.gisenv`
cp /tmp/au/aas_z55.DBF "$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/aas_z55.dbf"

# conectar la base de datos completa al mapa vectorial, usar como columna clave la columna "VALUE"
v.db.connect map=aas_z55 driver=dbf table=aas_z55 key=value

Y listo. Los datos están en la base de datos de GRASS.

Importar mallas ráster E00

Enlazar datos en GRASS

Es posible enlazar los datos, en vez de importarlos usando los comandos r.external, v.external, r.external.out, y v.external.out. Todos los datos deben tener la misma proyección que la Localización de GRASS.== See also ==

Links externos