1v.cluster(1)                  Grass User's Manual                 v.cluster(1)
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NAME

6       v.cluster  - Performs cluster identification.
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KEYWORDS

9       vector, point cloud, cluster, clump, level1
10

SYNOPSIS

12       v.cluster
13       v.cluster --help
14       v.cluster   [-2bt]   input=name   output=name   [layer=string]    [dis‐
15       tance=float]      [min=integer]      [method=string]      [--overwrite]
16       [--help]  [--verbose]  [--quiet]  [--ui]
17
18   Flags:
19       -2
20           Force 2D clustering
21
22       -b
23           Do not build topology
24           Advantageous when handling a large number of points
25
26       -t
27           Do not create attribute table
28
29       --overwrite
30           Allow output files to overwrite existing files
31
32       --help
33           Print usage summary
34
35       --verbose
36           Verbose module output
37
38       --quiet
39           Quiet module output
40
41       --ui
42           Force launching GUI dialog
43
44   Parameters:
45       input=name [required]
46           Name of input vector map
47           Or data source for direct OGR access
48
49       output=name [required]
50           Name for output vector map
51
52       layer=string
53           Layer number or name for cluster ids
54           Vector  features can have category values in different layers. This
55           number determines which layer to use. When  used  with  direct  OGR
56           access this is the layer name.
57           Default: 2
58
59       distance=float
60           Maximum distance to neighbors
61
62       min=integer
63           Minimum number of points to create a cluster
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65       method=string
66           Clustering method
67           Options: dbscan, dbscan2, density, optics, optics2
68           Default: dbscan
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DESCRIPTION

71       v.cluster partitions a point cloud into clusters or clumps.
72
73       If  the  minimum number of points is not specified with the min option,
74       the minimum number of points to  constitute  a  cluster  is  number  of
75       dimensions + 1, i.e. 3 for 2D points and 4 for 3D points.
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77       If  the maximum distance is not specified with the distance option, the
78       maximum distance is estimated from the observed distances to the neigh‐
79       bors using the upper 99% confidence interval.
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81       v.cluster  supports  different  methods for clustering. The recommended
82       methods are method=dbscan if all clusters should have a density  (maxi‐
83       mum distance between points) not larger than distance or method=density
84       if clusters should be created  separately  for  each  observed  density
85       (distance to the farthest neighbor).
86
87   dbscan
88       The  Density-Based  Spatial  Clustering of Applications with Noise is a
89       commonly used clustering algorithm. A new  cluster  is  started  for  a
90       point  with  at  least  min  - 1 neighbors within the maximum distance.
91       These neighbors are added to the cluster. The cluster is then  expanded
92       as  long  as at least min - 1 neighbors are within the maximum distance
93       for each point already in the cluster.
94
95   dbscan2
96       Similar to dbscan, but here it is sufficient if the  resultant  cluster
97       consists of at least min points, even if no point in the cluster has at
98       least min - 1 neighbors within distance.
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100   density
101       This method creates clusters according to their point density. The max‐
102       imum  distance is not used. Instead, the points are sorted ascending by
103       the distance to their farthest neighbor (core distance), inspecting min
104       - 1 neighbors. The densest cluster is created first, using as threshold
105       the core distance of the seed point. The cluster  is  expanded  as  for
106       DBSCAN,  with the difference that each cluster has its own maximum dis‐
107       tance. This method can identify clusters with different  densities  and
108       can create nested clusters.
109
110   optics
111       This method is Ordering Points to Identify the Clustering Structure. It
112       is controlled by the number of neighbor points (option min  -  1).  The
113       core  distance of a point is the distance to the farthest neighbor. The
114       reachability of a point q is its distance  from  a  point  p  (original
115       optics:  max(core-distance(p),  distance(p, q))). The aim of the optics
116       method is to reduce the reachability of each  point.  Each  unprocessed
117       point is the seed for a new cluster. Its neighbors are added to a queue
118       sorted by smallest reachability if their reachability can  be  reduced.
119       The  points  in the queue are processed and their unprocessed neighbors
120       are added to a queue sorted by smallest reachability if  their  reacha‐
121       bility can be reduced.
122
123       The  optics  method  does  not  create clusters itself, but produces an
124       ordered list of the points together with their reachability. The output
125       list  is  ordered according to the order of processing: the first point
126       processed is the first in the list, the last  point  processed  is  the
127       last in the list. Clusters can be extracted from this list by identify‐
128       ing valleys in the points’ reachability,  e.g.  by  using  a  threshold
129       value.  If  a  maximum  distance is specified, this is used to identify
130       clusters, otherwise each separated network will constitute a cluster.
131
132       The OPTICS algorithm uses each yet unprocessed point  to  start  a  new
133       cluster. The order of the input points is arbitrary and can thus influ‐
134       ence the resultant clusters.
135
136   optics2
137       EXPERIMENTAL This method is similar to OPTICS, minimizing  the  reacha‐
138       bility  of each point. Points are reconnected if their reachability can
139       be reduced. Contrary to OPTICS, a  cluster’s  seed  is  not  fixed  but
140       changed if possible. Each point is connected to another point until the
141       core of the cluster (seed point) is reached.  Effectively, the  initial
142       seed  is  updated in the process. Thus separated networks of points are
143       created, with each network representing a cluster. The maximum distance
144       is not used.
145

EXAMPLE

147       Analysis  of  random  points for areas in areas of the vector urbanarea
148       (North Carolina sample dataset).
149
150       First generate 1000 random points within the areas the vector urbanarea
151       and within the subregion, then do clustering and visualize the result:
152       # pick a subregion of the vector urbanarea
153       g.region -p n=272950 s=188330 w=574720 e=703090 res=10
154       # create random points in areas
155       v.random output=random_points npoints=1000 restrict=urbanarea
156       # identify clusters
157       v.cluster input=random_points output=clusters_optics method=optics
158       # set random vector color table for the clusters
159       v.colors map=clusters_optics layer=2 use=cat color=random
160       # display in command line
161       d.mon wx0
162       # note the second layer and transparent (none) color of the circle border
163       d.vect map=clusters_optics layer=2 icon=basic/point size=10 color=none
164
165         Figure:  Four different methods with default settings applied to 1000
166       random points generated in the same way as in  the  example.   Generate
167       random  points for analysis (100 points per area), use different method
168       for clustering and visualize using color stored the attribute table.
169       # pick a subregion of the vector urbanarea
170       g.region -p n=272950 s=188330 w=574720 e=703090 res=10
171       # create clustered points
172       v.random output=rand_clust npoints=100 restrict=urbanarea -a
173       # identify clusters
174       v.cluster in=rand_clust out=rand_clusters method=dbscan
175       # create colors for clusters
176       v.db.addtable map=rand_clusters layer=2 columns="cat integer,grassrgb varchar(11)"
177       v.colors map=rand_clusters layer=2 use=cat color=random rgb_column=grassrgb
178       # display with your preferred method
179       # remember to use the second layer and RGB column
180       # for example use
181       d.vect map=rand_clusters layer=2 color=none rgb_column=grassrgb icon=basic/circle
182

SEE ALSO

184        r.clump, v.hull, v.distance
185

AUTHOR

187       Markus Metz
188
189       Last changed: $Date: 2015-09-07 10:09:13 +0200 (Mon, 07 Sep 2015) $
190

SOURCE CODE

192       Available at: v.cluster source code (history)
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194       Main index | Vector index | Topics index | Keywords index  |  Graphical
195       index | Full index
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197       © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
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201GRASS 7.4.4                                                       v.cluster(1)
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