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v.outlier(1)		    GRASS GIS User's Manual		  v.outlier(1)

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=nameA [required]
	   Name	of input vector	map
	   Or data source for direct OGR access

       output=nameA [required]
	   Name	for output vector map

       outlier=nameA [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)

       Main index | Vector index | Topics index	| Keywords index  |  Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.4 Reference	Manual

GRASS 7.8.4							  v.outlier(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | EXAMPLES | NOTES | SEE ALSO | AUTHORS | SOURCE CODE

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