v.mkgrid(1grass) GRASS GIS User's Manual v.mkgrid(1grass)
NAME
v.mkgrid - Creates a vector map of a user-defined grid.
KEYWORDS
vector, geometry, grid, point pattern, hexagon
SYNOPSIS
v.mkgrid
v.mkgrid --help
v.mkgrid [-had] 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
-d
EXPERIMENTAL: Add diagonals to rectangular lines
Applies only to lines for rectangles
--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 op-
tion.
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 op-
tion.
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 quadran-
gles, 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 be-
fore 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 ef-
fect):
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
Using hexagons for point density
To compute point density in a hexagonal grid for the vector map
points_of_interest in the basic North Carolina sample dataset, the vec-
tor map itself is used to set extent of the computational region. The
resolution is based on the desired size of hexagons.
g.region vector=points_of_interest res=2000 -pa
The hexagonal grid is created as a vector map based on the previously
selected extent and size of the grid.
v.mkgrid map=hexagons -h
The following counts the number of points per hexagon using the
v.vect.stats module.
v.vect.stats points=points_of_interest areas=hexagons count_column=count
User should note that some of the points may be outside the grid since
the hexagons cannot cover all the area around the edges (the computa-
tional region extent needs to be enlarged if all points should be con-
sidered). The last command sets the vector map color table to viridis
based on the count column.
v.colors map=hexagons use=attr column=count color=viridis
Point density in a hexagonal grid
SEE ALSO
d.grid, v.in.region, v.patch, v.vect.stats
AUTHORS
Michael Higgins, U.S.Army Construction Engineering Research Laboratory
Update for new vectors Radim Blazek 10/2004
SOURCE CODE
Available at: v.mkgrid source code (history)
Accessed: unknown
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GRASS 7.8.7 v.mkgrid(1grass)
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