.TH v.hull 1grass "" "GRASS 6.4.4" "Grass User's Manual"
.SH NAME
\fI\fBv.hull\fR\fR  - Produces a convex hull for a given vector map.
.SH KEYWORDS
vector, geometry
.SH SYNOPSIS
\fBv.hull\fR
.br
\fBv.hull help\fR
.br
\fBv.hull\fR [\-\fBaf\fR] \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR] 
.SS Flags:
.IP "\fB\-a\fR" 4m
.br
Use all vector points (do not limit to current region)
.IP "\fB\-f\fR" 4m
.br
Create a 'flat' 2D hull even if the input is 3D points
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR" 4m
.br
Name of input vector map
.br
For vector lines reads their vertices
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output vector map
.PP
.SH DESCRIPTION
\fIv.hull\fR 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.
.PP
In the case of 3D input points, the hull will be a 3D hull as well,
unless the user specifies the \fB-f\fR flag. The 3D hull will be
composed of triangular faces.
.br
	| 
Fig: Convex hull polygon created with \fIv.hull\fR
.SH EXAMPLE
Example of \fIv.hull\fR 3D output (using two random 3D point  
clouds, North Carolina sample data set):
\fC
.DS
.br
g.region rural_1m \-p
.br
r.mapcalc "zero = 0"
.br
v.random \-z output=random3d_a n=10 zmin=0 zmax=200
.br
v.random \-z output=random3d_b n=15 zmin=400 zmax=600
.br
v.hull input=random3d_a output=random3d_a_hull
.br
v.hull input=random3d_b output=random3d_b_hull
.br
nviz elevation=zero vect=random3d_a_hull,random3d_b_hull
.br
.DE
\fR
.SH REFERENCES
.RE
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.
.RE
.SH SEE ALSO
\fI
v.delaunay
\fR
.SH AUTHOR
Andrea Aime, Modena, Italy
.br
Markus Neteler, ITC-irst (update to 5.7)
.br
Benjamin Ducke, CAU Kiel (3D hull support)
.br
Martin Landa, CTU in Prague, Czech Republic (vector lines support)
.PP
\fILast changed: $Date: 2013-04-14 10:55:49 +0200 (Sun, 14 Apr 2013) $\fR
.PP
Full index
.PP
© 2003-2014 GRASS Development Team