GRASS GIS manual: v.hull

NAME

v.hull - Produces a convex hull for a given vector map.

KEYWORDS

vector, geometry

SYNOPSIS

v.hull
v.hull help
v.hull [-af] input=name layer=string output=name [--overwrite] [--verbose] [--quiet]

Flags:

-a: Use all vector points (do not limit to current region)
-f: Create a 'flat' 2D hull even if the input is 3D points
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

input=name [required]: Name of input vector map; Or data source for direct OGR access
layer=string [required]: Layer number or name ('-1' for all layers); A single vector map can be connected to multiple database tables. This number determines which table to use. When used with direct OGR access this is the layer name.; Default: -1
output=name [required]: Name for output vector map

DESCRIPTION

v.hull computes the convex hull of a vector map and outputs the convex hull polygon as a vector area map. The convex hull, or convex envelope, for an object or a set of objects is the minimal convex set containing the given objects. This module creates a vector polygon containing all vector points or lines of the input map.

In the case of 3D input points, the hull will be a 3D hull as well, unless the user specifies the -f flag. The 3D hull will be composed of triangular faces.

Fig: Convex hull polygon created with v.hull

EXAMPLE

Example of v.hull 3D output (using two random 3D point clouds):

g.region rural_1m -p
r.mapcalc zero=0
v.random -z output=random3d_a n=10 zmin=0 zmax=200
v.random -z output=random3d_b n=15 zmin=400 zmax=600
v.hull input=random3d_a output=random3d_a_hull
v.hull input=random3d_b output=random3d_b_hull
nviz elevation=zero vect=random3d_a_hull,random3d_b_hull

REFERENCES

M. de Berg, M. van Kreveld, M. Overmars, O. Schwarzkopf, (2000). Computational geometry, chapter 1.1, 2-8.
J. O'Rourke, (1998). Computational Geometry in C (Second Edition), chapter 4.

AUTHOR

Andrea Aime, Modena, Italy
Markus Neteler, ITC-irst (update to 5.7)
Benjamin Ducke, CAU Kiel (3D hull support)
Martin Landa, CTU in Prague, Czech Republic (vector lines support)

Last changed: $Date: 2011-11-08 13:24:20 -0800 (Tue, 08 Nov 2011) $

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