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 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.

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 dataset 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: Thursday Oct 30 22:18:13 2025

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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual