v.mkgrid.1grass man page

v.mkgrid — Creates a vector map of a user-defined grid.

Keywords

vector, geometry, grid, point pattern

Synopsis

v.mkgrid
v.mkgrid --help
v.mkgrid [-ha] map=name [grid=rows,columns] [position=string] [coordinates=east,north] [box=width,height] [angle=float] [breaks=integer] [type=string] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags

-h
Create hexagons (default: rectangles)
-a
Allow asymmetric hexagons
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog

Parameters

map=name [required]
Name for output vector map
grid=rows,columns
Number of rows and columns in grid
position=string
Where to place the grid
Options: region, coor
Default: region
region: current region
coor: use ’coor’ and ’box’ options
coordinates=east,north
Lower left easting and northing coordinates of map
box=width,height
Width and height of boxes in grid
angle=float
Angle of rotation (in degrees counter-clockwise)
Default: 0
breaks=integer
Number of vertex points per grid cell
Options: 0-60
Default: 0
type=string
Output feature type
Options: point, line, area
Default: area

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: 2014-12-28 00:21:19 +0100 (Sun, 28 Dec 2014) $

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