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v.outlier(1) Grass User's Manual v.outlier(1)

v.outlier - Removes outliers from vector point data.

vector, statistics, extract, select, filter, LIDAR

v.outlier
 
v.outlier --help
 
v.outlier [-e] input=name output=name outlier=name [qgis=name] [ew_step=float] [ ns_step=float] [lambda=float] [threshold=float] [filter=string] [--overwrite] [--help] [--verbose] [-- quiet] [--ui]

-e
 
Estimate point density and distance
 
Estimate point density and distance for the input vector points within the current region extends and quit
--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
 
Or data source for direct OGR access
output=name [required]
 
Name for output vector map
outlier=name [required]
 
Name for output outlier vector map
qgis=name
 
Name for vector map for visualization in QGIS
ew_step=float
 
Length of each spline step in the east-west direction
 
Default: 10 * east-west resolution
ns_step=float
 
Length of each spline step in the north-south direction
 
Default: 10 * north-south resolution
lambda=float
 
Tykhonov regularization weight
 
Default: 0.1
threshold=float
 
Threshold for the outliers
 
Default: 50
filter=string
 
Filtering option
 
Options: both, positive, negative
 
Default: both

v.outlier removes outliers in a 3D point cloud. By default, the outlier identification is done by a bicubic spline interpolation of the observation with a high regularization parameter and a low resolution in south-north and east-west directions. Those points that differ in an absolute value more than the given threshold from a fixed value, reckoned from its surroundings by the interpolation, are considered as an outlier, and hence are removed.
The filter option specifies if all outliers will be removed (default), or only positive or only negative outliers. Filtering out only positive outliers can be useful to filter out vegetation returns (e.g. from forest canopies) from LIDAR point clouds, in order to extract Digital Terrain Models. Filtering out only negative outliers can be useful to estimate vegetation height.
There is a flag to create a vector that can be visualizated by qgis. That means that topology is build and the z coordinate is considered as a category.

v.outlier input=vector_map output=vector_output outlier=vector_outlier thres_O=25
In this case, a basic outlier removal is done with a threshold of 25 m.

v.outlier input=vector_map output=vector_output outlier=vector_outlier qgis=vector_qgis
Now, the outlier removal uses the default threshold and there is also an output vector available for visualizaton in QGIS (http://www.qgis.org).

v.outlier input=elev_lid792_bepts output=elev_lid792_bepts_nooutliers \
  outlier=elev_lid792_bepts_outliers ew_step=5 ns_step=5 thres_o=0.1

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

v.surf.bspline

Original version of the program in GRASS 5.4:
 
Maria Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko Reguzzoni
 
 
Updates for GRASS 6:
 
Roberto Antolin
Last changed: $Date: 2014-08-05 08:59:29 +0200 (Tue, 05 Aug 2014) $

Available at: v.outlier source code (history)
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© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference Manual
GRASS 7.4.3

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