v.kernelgrass - Online in the Cloud

PROGRAM:

NAME

v.kernel - Generates a raster density map from vector points map.
Density is computed using a moving kernel. Optionally generates a vector 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 radius=float [dsize=float]
[segmax=float] [distmax=float] [multiplier=float] [node=string] [kernel=string]
[--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 * mult

-m
In network mode, multiply the result by number of input points

--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 [required]
Name for output raster/vector map
Outputs vector map if network map is given, otherwise raster map

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, triangular, 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 overestimating 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 resulting 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 optimal 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.

LIMITATIONS

The module only considers the presence of points, but not (yet) any attribute values.

REFERENCES

· Okabe, A., Satoh, T., Sugihara, K. (2009). A kernel density estimation method for
networks, its computational method and a GIS-based tool. International Journal of
Geographical Information Science, Vol 23(1), pp. 7-32.
DOI: 10.1080/13658810802475491

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