NAME

       v.outlier  - Removes outliers from vector point data.

KEYWORDS

       vector, statistics, extract, select, filter

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 of output outlier vector map

       qgis=name
           Name of vector map for visualization in QGIS

       ew_step=float
           Length of each spline step in the east-west direction
           Default: 10

       ns_step=float
           Length of each spline step in the north-south direction
           Default: 10

       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

       Last changed: $Date: 2014-08-05 09:02:35 +0200 (Tue, 05 Aug 2014) $

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