1v.kernel(1) GRASS GIS User's Manual v.kernel(1)
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6 v.kernel - Generates a raster density map from vector points map.
7 Density is computed using a moving kernel. Optionally generates a vec‐
8 tor density map on a vector network.
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11 vector, kernel density, point density, heatmap, hotspot
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14 v.kernel
15 v.kernel --help
16 v.kernel [-oqnm] input=name [net=name] [output=name] [net_out‐
17 put=name] radius=float [dsize=float] [segmax=float] [dist‐
18 max=float] [multiplier=float] [node=string] [kernel=string]
19 [--overwrite] [--help] [--verbose] [--quiet] [--ui]
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21 Flags:
22 -o
23 Try to calculate an optimal radius with given ’radius’ taken as
24 maximum (experimental)
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26 -q
27 Only calculate optimal radius and exit (no map is written)
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29 -n
30 In network mode, normalize values by sum of density multiplied by
31 length of each segment. Integral over the output map then gives 1.0
32 * multiplier
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34 -m
35 In network mode, multiply the result by number of input points
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37 --overwrite
38 Allow output files to overwrite existing files
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40 --help
41 Print usage summary
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43 --verbose
44 Verbose module output
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46 --quiet
47 Quiet module output
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49 --ui
50 Force launching GUI dialog
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52 Parameters:
53 input=name [required]
54 Name of input vector map with training points
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56 net=name
57 Name of input network vector map
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59 output=name
60 Name for output raster map
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62 net_output=name
63 Name for output vector density map
64 Outputs vector map if network map is given
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66 radius=float [required]
67 Kernel radius in map units
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69 dsize=float
70 Discretization error in map units
71 Default: 0.
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73 segmax=float
74 Maximum length of segment on network
75 Default: 100.
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77 distmax=float
78 Maximum distance from point to network
79 Default: 100.
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81 multiplier=float
82 Multiply the density result by this number
83 Default: 1.
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85 node=string
86 Node method
87 Options: none, split
88 Default: none
89 none: No method applied at nodes with more than 2 arcs
90 split: Equal split (Okabe 2009) applied at nodes
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92 kernel=string
93 Kernel function
94 Options: uniform, triangular, epanechnikov, quartic, triweight,
95 gaussian, cosine
96 Default: gaussian
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99 v.kernel generates a raster density map from vector points data using a
100 moving kernel. Available kernel density functions are uniform, triangu‐
101 lar, epanechnikov, quartic, triweight, gaussian, cosine, default is
102 gaussian.
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104 The module can also generate a vector density map on a vector network.
105 Conventional kernel functions produce biased estimates by overestimat‐
106 ing the densities around network nodes, whereas the equal split method
107 of Okabe et al. (2009) produces unbiased density estimates. The equal
108 split method uses the kernel function selected with the kernel option
109 and can be enabled with node=split.
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112 The multiplier option is needed to overcome the limitation that the
113 resulting density in case of a vector map output is stored as category
114 (integer). The density result stored as category may be multiplied by
115 this number.
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117 For the gaussian kernel, standard deviation for the gaussian function
118 is set to 1/4 of the radius.
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120 With the -o flag (experimental) the command tries to calculate an opti‐
121 mal radius. The value of radius is taken as maximum value. The radius
122 is calculated based on the gaussian function, using ALL points, not
123 just those in the current region.
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126 Compute density of points (using vector map of schools from North Car‐
127 olina sample dataset):
128 g.region region=wake_30m
129 v.kernel input=schools_wake output=schools_density radius=5000 multiplier=1000000
130 r.colors map=schools_density color=bcyr
131 School density
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134 The module only considers the presence of points, but not (yet) any
135 attribute values.
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138 · Okabe, A., Satoh, T., Sugihara, K. (2009). A kernel density
139 estimation method for networks, its computational method and a
140 GIS-based tool. International Journal of Geographical Informa‐
141 tion Science, Vol 23(1), pp. 7-32.
142 DOI: 10.1080/13658810802475491
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145 v.surf.rst
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147 Overview: Interpolation and Resampling in GRASS GIS
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150 Stefano Menegon, ITC-irst, Trento, Italy
151 Radim Blazek (additional kernel density functions and network part)
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154 Available at: v.kernel source code (history)
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156 Main index | Vector index | Topics index | Keywords index | Graphical
157 index | Full index
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159 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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163GRASS 7.8.5 v.kernel(1)