v.kernel(1grass) GRASS GIS User's Manual v.kernel(1grass)
NAME
v.kernel - Generates a raster density map from vector points map.
Density is computed using a moving kernel. Optionally generates a vec-
tor density map on a vector network.
KEYWORDS
vector, kernel density, point density, heatmap, hotspot
SYNOPSIS
v.kernel
v.kernel --help
v.kernel [-oqnm] input=name [net=name] [output=name] [net_out-
put=name] radius=float [dsize=float] [segmax=float] [dist-
max=float] [multiplier=float] [node=string] [kernel=string]
[--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-o
Try to calculate an optimal radius with given ’radius’ taken as
maximum (experimental)
-q
Only calculate optimal radius and exit (no map is written)
-n
In network mode, normalize values by sum of density multiplied by
length of each segment. Integral over the output map then gives 1.0
* multiplier
-m
In network mode, multiply the result by number of input points
--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:
input=name [required]
Name of input vector map with training points
net=name
Name of input network vector map
output=name
Name for output raster map
net_output=name
Name for output vector density map
Outputs vector map if network map is given
radius=float [required]
Kernel radius in map units
dsize=float
Discretization error in map units
Default: 0.
segmax=float
Maximum length of segment on network
Default: 100.
distmax=float
Maximum distance from point to network
Default: 100.
multiplier=float
Multiply the density result by this number
Default: 1.
node=string
Node method
Options: none, split
Default: none
none: No method applied at nodes with more than 2 arcs
split: Equal split (Okabe 2009) applied at nodes
kernel=string
Kernel function
Options: uniform, triangular, epanechnikov, quartic, triweight,
gaussian, cosine
Default: gaussian
DESCRIPTION
v.kernel generates a raster density map from vector points data using a
moving kernel. Available kernel density functions are uniform, triangu-
lar, epanechnikov, quartic, triweight, gaussian, cosine, default is
gaussian.
The module can also generate a vector density map on a vector network.
Conventional kernel functions produce biased estimates by overestimat-
ing the densities around network nodes, whereas the equal split method
of Okabe et al. (2009) produces unbiased density estimates. The equal
split method uses the kernel function selected with the kernel option
and can be enabled with node=split.
NOTES
The multiplier option is needed to overcome the limitation that the re-
sulting density in case of a vector map output is stored as category
(integer). The density result stored as category may be multiplied by
this number.
For the gaussian kernel, standard deviation for the gaussian function
is set to 1/4 of the radius.
With the -o flag (experimental) the command tries to calculate an opti-
mal radius. The value of radius is taken as maximum value. The radius
is calculated based on the gaussian function, using ALL points, not
just those in the current region.
EXAMPLES
Compute density of points (using vector map of schools from North Car-
olina sample dataset):
g.region region=wake_30m
v.kernel input=schools_wake output=schools_density radius=5000 multiplier=1000000
r.colors map=schools_density color=bcyr
School density
KNOWN ISSUES
The module only considers the presence of points, but not (yet) any at-
tribute values.
REFERENCES
• Okabe, A., Satoh, T., Sugihara, K. (2009). A kernel density es-
timation method for networks, its computational method and a
GIS-based tool. International Journal of Geographical Informa-
tion Science, Vol 23(1), pp. 7-32.
DOI: 10.1080/13658810802475491
SEE ALSO
v.surf.rst
Overview: Interpolation and Resampling in GRASS GIS
AUTHORS
Stefano Menegon, ITC-irst, Trento, Italy
Radim Blazek (additional kernel density functions and network part)
SOURCE CODE
Available at: v.kernel source code (history)
Accessed: unknown
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GRASS 7.8.7 v.kernel(1grass)
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