.TH v.hull 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.hull\fR\fR  \- Produces a 2D/3D convex hull for a given vector map.
.SH KEYWORDS
vector, geometry, 3D
.SH SYNOPSIS
\fBv.hull\fR
.br
\fBv.hull \-\-help\fR
.br
\fBv.hull\fR [\-\fBrf\fR] \fBinput\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]  \fBoutput\fR=\fIname\fR  [\fBcats\fR=\fIrange\fR]   [\fBwhere\fR=\fIsql_query\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-r\fR" 4m
.br
Limit to current region
.IP "\fB\-f\fR" 4m
.br
Create a \(cqflat\(cq 2D hull even if the input is 3D points
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector map
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name (\(cq\-1\(cq for all layers)
.br
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.
.br
Default: \fI\-1\fR
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output vector map
.IP "\fBcats\fR=\fIrange\fR" 4m
.br
Category values
.br
Example: 1,3,7\-9,13
.IP "\fBwhere\fR=\fIsql_query\fR" 4m
.br
WHERE conditions of SQL statement without \(cqwhere\(cq keyword
.br
Example: income < 1000 and population >= 10000
.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 NOTES
In order to use the \fBwhere\fR option the \fBlayer\fR option must
be set to a positive number (the default is \(cq\-1\(cq for \(cqall layers\(cq), otherwise
all points from all layers will be used and the \fBcats\fR and \fBwhere\fR
options will be ignored.
.SH EXAMPLE
Example of \fIv.hull\fR 3D output (using two random 3D point
clouds, North Carolina sample data set):
.br
.nf
\fC
g.region rural_1m \-p
r.mapcalc \(dqzero = 0\(dq
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
d.mon wx0
d.vect random3d_a_hull
d.vect random3d_a color=red
d.vect random3d_b_hull
d.vect random3d_b color=red
# 3D view in wxGUI (g.gui)
\fR
.fi
.br
Fig: Convex hull in 3D from 3D points created with \fIv.hull\fR
.SH REFERENCES
.RS 4n
.IP \(bu 4n
M. de Berg, M. van Kreveld, M. Overmars, O. Schwarzkopf,
(2000). Computational geometry, chapter 1.1, 2\-8.
.IP \(bu 4n
J. O\(cqRourke, (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)
.SH SOURCE CODE
.PP
Available at: v.hull source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual