DESCRIPTION

v.select allows the user to select features from a vector map by features from another one.

Supported operators (without GEOS):

Supported operators (with GEOS):

NOTES

Only features with category numbers will be considered. If required the v.category module can be used to add them. Typically boundaries do not need to be given a category number, as an area's attributes are inherited from the centroid. Typically points, lines, and centroids will always want to have a cat number. E.g. take a road which separates two farms. It is ambiguous as to which farm an attribute that is attached to the road belongs to. The boundary only needs a cat number if it will hold its own attributes, such as road name or pavement form. A centroid in each paddock holds the information with respect to ownership, area, etc.

EXAMPLES

Extract fire stations (points) falling into urban area (polygon) - North Carolina data set (point in polygon test): 
v.select ainput=firestations binput=urbanarea output=urban_firestations \
         operator=overlap
Extract railroad lines from zip code map overlapping with the urban area (line in polygon test): 
v.select ainput=railroads binput=urbanarea \
         output=railroads_in_urbanarea operator=overlap
Extract those areas from zip code map which overlap with railroads (polygon on line test): 
# first add a tiny buffer around railroad lines:
v.buffer input=railroads output=railroads_buf20m \
  distance=20

v.select ainput=zipcodes_wake binput=railroads_buf20m \
  output=zipcodes_wake_railroads operator=overlap

TODO

Processing areas with GEOS is currently incredibly slow. Significant speed-up is desired.

SEE ALSO

v.category, v.overlay, v.extract

GRASS SQL interface

AUTHORS

Radim Blazek
GEOS support by Martin Landa, Czech Technical University in Prague, Czech Republic

Last changed: $Date$