1v.outlier(1)                GRASS GIS User's Manual               v.outlier(1)
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NAME

6       v.outlier  - Removes outliers from vector point data.
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KEYWORDS

9       vector, statistics, extract, select, filter, LIDAR
10

SYNOPSIS

12       v.outlier
13       v.outlier --help
14       v.outlier   [-e]   input=name   output=name  outlier=name   [qgis=name]
15       [ew_step=float]   [ns_step=float]   [lambda=float]    [threshold=float]
16       [filter=string]     [--overwrite]    [--help]   [--verbose]   [--quiet]
17       [--ui]
18
19   Flags:
20       -e
21           Estimate point density and distance
22           Estimate point density and distance for  the  input  vector  points
23           within the current region extends and quit
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25       --overwrite
26           Allow output files to overwrite existing files
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28       --help
29           Print usage summary
30
31       --verbose
32           Verbose module output
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34       --quiet
35           Quiet module output
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37       --ui
38           Force launching GUI dialog
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40   Parameters:
41       input=name [required]
42           Name of input vector map
43           Or data source for direct OGR access
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45       output=name [required]
46           Name for output vector map
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48       outlier=name [required]
49           Name for output outlier vector map
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51       qgis=name
52           Name for vector map for visualization in QGIS
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54       ew_step=float
55           Length of each spline step in the east-west direction
56           Default: 10 * east-west resolution
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58       ns_step=float
59           Length of each spline step in the north-south direction
60           Default: 10 * north-south resolution
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62       lambda=float
63           Tykhonov regularization weight
64           Default: 0.1
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66       threshold=float
67           Threshold for the outliers
68           Default: 50
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70       filter=string
71           Filtering option
72           Options: both, positive, negative
73           Default: both
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DESCRIPTION

76       v.outlier removes outliers in a 3D point cloud. By default, the outlier
77       identification is done by a bicubic spline interpolation of the  obser‐
78       vation  with  a  high  regularization parameter and a low resolution in
79       south-north and east-west directions. Those points that  differ  in  an
80       absolute  value more than the given threshold from a fixed value, reck‐
81       oned from its surroundings by the interpolation, are considered  as  an
82       outlier, and hence are removed.
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84       The  filter option specifies if all outliers will be removed (default),
85       or only positive or only negative outliers. Filtering out only positive
86       outliers can be useful to filter out vegetation returns (e.g. from for‐
87       est canopies) from LIDAR point clouds, in order to extract Digital Ter‐
88       rain  Models.  Filtering  out  only  negative outliers can be useful to
89       estimate vegetation height.
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91       There is a flag to create a vector that can be  visualizated  by  qgis.
92       That means that topology is build and the z coordinate is considered as
93       a category.
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EXAMPLES

96   Basic outlier removal
97       v.outlier input=vector_map output=vector_output outlier=vector_outlier thres_O=25
98       In this case, a basic outlier removal is done with a threshold of 25 m.
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100   Basic outlier removal
101       v.outlier input=vector_map output=vector_output outlier=vector_outlier qgis=vector_qgis
102       Now, the outlier removal uses the default threshold and there  is  also
103       an    output    vector    available    for    visualizaton    in   QGIS
104       (http://www.qgis.org).
105
106   North carolina location example
107       v.outlier input=elev_lid792_bepts output=elev_lid792_bepts_nooutliers \
108         outlier=elev_lid792_bepts_outliers ew_step=5 ns_step=5 thres_o=0.1
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NOTES

111       This module is designed to work with LIDAR data,  so  not  topology  is
112       built but in the QGIS output.
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SEE ALSO

115       v.surf.bspline
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AUTHORS

118       Original version of the program in GRASS 5.4:
119       Maria  Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko
120       Reguzzoni
121       Updates for GRASS 6:
122       Roberto Antolin
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SOURCE CODE

125       Available at: v.outlier source code (history)
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127       Main index | Vector index | Topics index | Keywords index  |  Graphical
128       index | Full index
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130       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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134GRASS 7.8.5                                                       v.outlier(1)
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