DESCRIPTION

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

Supported operators (without GEOS; using GRASS' own algorithm):

Supported operators (internally using GEOS - Geometry Engine, Open Source):

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

Preparation of example data (North Carolina sample dataset): 
# Create an grid for overlaying to ZIP code vector map
v.mkgrid map=boxgrid grid=10,10 position=coor \
         coordinates=583600,201500 box=5000,5000

# set region to ZIP codes and boxgrid vector maps
g.region vector=zipcodes_wake,boxgrid -p res=100 -a
# enlarge region a bit for "white border" around map in monitor
g.region n=n+1000 s=s-1000 w=w-1000 e=e+1000 -p
d.mon wx0

OVERLAP: features partially or completely overlap (using GRASS)

Select grid boxes (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=boxgrid fill_color=85:130:176
v.select ainput=boxgrid binput=zipcodes_wake output=v_select_OVERLAP operator=overlap
d.vect map=v_select_OVERLAP
d.vect map=zipcodes_wake type=boundary color=50:50:50
v.select with OVERLAP operator
v.select with OVERLAP operator: selected grid boxes shown in grey

OVERLAPS features spatially overlap (using GEOS)

Select grid boxes (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=boxgrid fill_color=85:130:176
v.select ainput=boxgrid binput=zipcodes_wake output=v_select_OVERLAPS operator=overlaps
d.vect map=v_select_OVERLAPS
d.vect map=zipcodes_wake type=boundary color=50:50:50
v.select with OVERLAPS operator
v.select with OVERLAPS operator: selected grid boxes shown in grey

DISJOINT: features do not spatially intersect (using GEOS)

Select grid boxes (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=boxgrid fill_color=85:130:176
v.select ainput=boxgrid binput=zipcodes_wake output=v_select_DISJOINT operator=disjoint
d.vect map=v_select_DISJOINT
d.vect map=zipcodes_wake type=boundary color=50:50:50
v.select with DISJOINT operator
v.select with DISJOINT operator: selected grid boxes shown in grey

EQUALS: features are spatially equals (using GEOS)

Select zipcode polygon (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
v.extract input=zipcodes_wake where=ZIPCODE_ID=35 output=zipcodeID35
v.select ainput=zipcodes_wake binput=zipcodeID35 output=v_select_EQUALS operator=equals
d.vect map=v_select_EQUALS
d.vect map=zipcodes_wake type=boundary color=50:50:50
v.select with EQUALS operator
v.select with EQUALS operator: selected grid boxes shown in grey

INTERSECTS: features spatially intersect (using GEOS)

Select zipcode polygons (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=boxgrid fill_color=85:130:176
v.select ainput=zipcodes_wake binput=boxgrid output=v_select_INTERSECTS operator=intersects
d.vect map=v_select_INTERSECTS
d.vect map=boxgrid type=boundary color=50:50:50
v.select with INTERSECTS operator
v.select with INTERSECTS operator: selected grid boxes shown in grey

TOUCHES: features spatially touches (using GEOS)

Select polygons (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=zipcodeID35 fill_color=85:130:176
v.select ainput=zipcodes_wake binput=zipcodeID35 output=v_select_TOUCHES operator=touches
d.vect map=v_select_TOUCHES
d.vect map=zipcodes_wake type=boundary color=50:50:50
v.select with TOUCHES operator
v.select with TOUCHES operator: selected polygons shown in grey (blue: input polygon)

CROSSES: features spatially crosses (using GEOS)

Select zipcode polygons by lines (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=busroute1 color=200:27:27 width=3
v.select ainput=zipcodes_wake binput=busroute1 output=v_select_CROSSES operator=crosses
d.vect map=v_select_CROSSES
d.vect map=zipcodes_wake type=boundary color=50:50:50
d.vect map=busroute1 color=200:27:27 width=3
v.select with CROSSES operator
v.select with CROSSES operator: selected polygons shown in grey (red: input lines)

WITHIN feature A is completely inside feature B (using GEOS)

Select zipcode polygons (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=boundary_county fill_color=85:130:176
v.select ainput=zipcodes_wake binput=boundary_county output=v_select_WITHIN operator=within
d.vect map=v_select_WITHIN
v.select with WITHIN operator
v.select with WITHIN operator: selected polygons shown in grey (blue: input polygons)

CONTAINS feature B is completely inside feature A (using GEOS)

Select zipcode polygon (North Carolina sample dataset):

CONTAINS with polygons

d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=zipcodeID35 fill_color=85:130:176
v.select ainput=zipcodes_wake binput=zipcodeID35 \
         output=v_select_CONTAINS_pol operator=contains
d.vect map=v_select_CONTAINS
v.select with CONTAINS operator
v.select with CONTAINS operator: selected polygon shown in grey (blue: input polygon, not visible)

CONTAINS with points

d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=hospitals fill_color=195:31:31 icon=basic/cross3 size=10
v.select ainput=zipcodes_wake binput=hospitals \
         output=v_select_CONTAINS_pnts operator=contains
d.vect map=v_select_CONTAINS_pnts
d.vect map=hospitals fill_color=195:31:31 icon=basic/cross3 size=10
v.select with CONTAINS operator
v.select with CONTAINS operator: selected polygons shown in grey (red: input points)

RELATE feature A is spatially related to feature B (using GEOS)

This operator additionally requires the relate parameter (in other GIS called 'ST_Relate'). This operator allows calculating the Dimensionally Extended nine-Intersection Model (DE-9IM). In the following one example: Select polygon with 'TOUCHES' operator (North Carolina sample dataset): 
d.vect map=zipcodes_wake fill_color=0:128:0
d.vect map=zipcodeID35 fill_color=85:130:176
v.select ainput=zipcodeID35 binput=zipcodes_wake \
         output=v_select_TOUCHES_relate operator=relate relate='T********'
d.vect map=v_select_TOUCHES
The result of relate='T********' is the same as seen above in the example 'TOUCHES'. See the DE-9IM page for related operators and their definition.

Extraction of points falling into a polygon

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

Extraction of lines overlapping with a polygon

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

Extraction of areas overlapping with a line

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

SEE ALSO

v.category, v.clip, v.overlay, v.extract

GRASS SQL interface
GEOS - Geometry Engine, Open Source

AUTHORS

Radim Blazek
GEOS support by Martin Landa, Czech Technical University in Prague, Czech Republic
ZIP code examples by Carol X. Garzon-Lopez, Trento, Italy

Last changed: $Date$