DESCRIPTION
v.mkgrid creates a vector map representation of a regular
coordinate grid. Point, line, and area vector grids can be created.
NOTES
Grid points created with the type=point option will be placed at
the center of each grid cell, like centroids with the default
type=area option.
Grid lines created with the type=line option will be identical to
the edges of each grid cell, like boundaries with the default
type=area option.
The resultant grid can be rotated around the origin (center of the
grid) with the angle option.
Optionally hexagons can be created with the -h flag. Hexagons
are by default symmetric. Asymmetric hexagons can be allowed with the
-a flag.
This module is NOT to be used to generate a vector map of USGS
quadrangles, because USGS quads are not exact rectangles.
EXAMPLES
Creating a global grid in a latitude-longitude
To be run in a latitude-longitude location (WGS84)
# set the region:
g.region n=90 s=-90 w=-180 e=180 res=10 -p
projection: 3 (Latitude-Longitude)
zone: 0
datum: wgs84
ellipsoid: wgs84
north: 90N
south: 90S
west: 180W
east: 180E
nsres: 10
ewres: 10
rows: 18
cols: 36
cells: 648
# create 10 degree size grid:
v.mkgrid map=grid_10deg
# create 20 degree size grid:
v.mkgrid map=grid_20deg box=20,20
Creating a grid in a metric projection
Creating a 4x3 grid, cells 20km a side, with lower left corner at 2716500,6447000:
v.mkgrid map=coro_grid grid=4,3 position=coor coordinates=2716500,6447000 box=20000,20000
Creating a positioned grid in a latitude-longitude
Creating a 10x12 lat/lon grid, cells 2 arc-min a side, with lower left corner
at 167deg 52min east, 47deg 6min south. For use with e.g. QGIS you can then
pull this grid into a projected location with v.proj before
exporting as a Shapefile with v.out.ogr (within GRASS GIS you could
just use d.grid -w from the projected location for the same effect):
v.mkgrid map=p2min_grid grid=10,12 position=coor coordinates=167:52E,47:06S box=0:02,0:02
Creating a simple point pattern
North Carolina sample dataset example, creating a 1km spaced point grid
based on the current region extent defined by the "elevation" map:
g.region raster=elevation res=1000 -pa
v.mkgrid type=point map=pointpattern
Creating a regular point pattern
North Carolina sample dataset example, creating a regular spaced point grid
based on the current region extent defined by the "elevation" map, using
a two-step approach:
# create first set of points, covering extent of "elevation" raster map
g.region raster=elevation res=1000 -pa
v.mkgrid type=point map=pointpattern1
# shift grid by half point distance (map units)
g.region n=n+500 w=w+500 e=e+500 s=s+500 -p
# create second set of points
v.mkgrid type=point map=pointpattern2
# merge into final point pattern
v.patch input=pointpattern1,pointpattern2 output=pointpattern3
Different point patterns for sampling design
Creating hexagons in a metric projection
North Carolina sample dataset example, creating regular hexagons
based on the current region extent defined by the "elevation" map and
raster resolution for the hexagon size:
g.region raster=elevation res=5000 -pa
v.mkgrid map=hexagons -h
d.grid 5000
Hexagon map
SEE ALSO
d.grid,
v.in.region,
v.patch
AUTHORS
Michael Higgins,
U.S.Army Construction Engineering
Research Laboratory
Update for new vectors Radim Blazek 10/2004
Last changed: $Date$