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 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: Monday Apr 01 03:08:50 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                    v.outlier(1grass)