GRASS GIS manual: v.centerpoint

NAME

v.centerpoint - Calculate center points

KEYWORDS

SYNOPSIS

v.centerpoint

v.centerpoint --help

v.centerpoint [-b] input=name [output=name] [type=string[,string,...]] [layer=string] [cats=range] [where=sql_query] [pcenter=string[,string,...]] [lcenter=string[,string,...]] [acenter=string[,string,...]] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-b: Do not build topology; Advantageous when handling a large number of points
--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: Name for output vector map
type=string[,string,...]: Input feature type; Options: point, line, area; Default: point,line,area
layer=string: Layer number or name; Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.; Default: 1
cats=range: Category values; Example: 1,3,7-9,13
where=sql_query: WHERE conditions of SQL statement without 'where' keyword; Example: income < 1000 and population >= 10000
pcenter=string[,string,...]: point center; Options: mean, median, pmedian; Default: mean; mean: Center of gravity; median: Geometric median (point of minimum distance); pmedian: Point closest to geometric median
lcenter=string[,string,...]: line center; Options: mid, mean, median; Default: mid; mid: Line mid point; mean: Center of gravity; median: Geometric median (point of minimum distance) using line segments
acenter=string[,string,...]: area center; Options: mean, median, bmedian; Default: mean; mean: Center of gravity; median: Geometric median (point of minimum distance) using area sizes; bmedian: Geometric median (point of minimum distance) using boundary segments

DESCRIPTION
EXAMPLE
SEE ALSO
AUTHOR

DESCRIPTION

v.centerpoint calculates center points for point clouds, lines and areas. Center points can be centers of gravity (coordinates' mean) or geometric medians (points of minimum distance, which is more robust in case of outliers.

For points, center points are calculated considering all points. For lines and areas, center points are calculated for each line or area separately.

If no output vector is given, center points are printed to stdout in ASCII point format:

<easting>|<northing>|<height>|<cat>

The category values are

1 - mean of points
2 - median of points
3 - point closest to median of points
4 - mid point of each line
5 - mean of each line
6 - median of each line
7 - mean of each area
8 - median of each area using area triangulation
9 - median of each area using boundaries

If an output vector is given, categories of the respective lines and areas are transferred from the selected layer to layer 1. Layer 2 holds the same category values as for output to stdout.

Point centers

mean - center of gravity, mean of all point coordinates
median - geometric median, minimum distance to all points
pmedian - point closest to the geometric median

Line centers

mid - the mid point of each line, lies exactly on the line
mean - center of gravity, mean of all line segments, might not lie on the line
median - geometric median, minimum distance to all line segments, might not lie on the line

Area centers

mean - center of gravity, calculated using area triangulation
median - geometric median, minimum distance to area triangulation, might not lie inside the area
bmedian - geometric median, minimum distance to boundary segments, might not lie inside the area

EXAMPLE

Calculate center of gravity for the LiDAR point cloud 'elev_lid_bepts' in the North Carolina sample dataset:

v.centerpoint input=elev_lid_bepts output=elev_lid_bepts_mean

v.centerpoint in=urbanarea out=urbanarea_median acenter=median

AUTHOR

Markus Metz

Last changed: $Date: 2014-02-03 09:22:15 +0100 (Mon, 03 Feb 2014) $

SOURCE CODE

Available at: v.centerpoint source code (history)