Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

Density is computed using a moving kernel. Optionally generates a vector density map on a vector network.

**-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

**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*

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**.

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.

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

- 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

Overview: Interpolation and Resampling in GRASS GIS

Radim Blazek (additional kernel density functions and network part)

Available at: v.kernel source code (history)

Latest change: Fri Jul 24 17:54:51 2020 in commit: 67e1a164149aaa2c412f93cd897ca4122da44c81

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

© 2003-2023 GRASS Development Team, GRASS GIS 7.8.8dev Reference Manual