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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 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
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 vector 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 computational region extent needs to be enlarged if all points should be
considered). 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)
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