v.outlier(1grass) GRASS GIS User's Manual v.outlier(1grass)
NAME
v.outlier - Removes outliers from vector point data.
KEYWORDS
vector, statistics, extract, select, filter, LIDAR
SYNOPSIS
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]
Flags:
-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
Parameters:
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
DESCRIPTION
v.outlier removes outliers in a 3D point cloud. By default, the outlier
identification is done by a bicubic spline interpolation of the obser-
vation 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, reck-
oned 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 for-
est canopies) from LIDAR point clouds, in order to extract Digital Ter-
rain Models. Filtering out only negative outliers can be useful to es-
timate 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.
EXAMPLES
Basic outlier removal
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.
Basic outlier removal
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).
North carolina location example
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
NOTES
This module is designed to work with LIDAR data, so not topology is
built but in the QGIS output.
SEE ALSO
v.surf.bspline
AUTHORS
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
SOURCE CODE
Available at: v.outlier source code (history)
Accessed: unknown
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GRASS 7.8.7 v.outlier(1grass)
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