v.hull(1grass) GRASS GIS User's Manual v.hull(1grass)
NAME
v.hull - Produces a 2D/3D convex hull for a given vector map.
KEYWORDS
vector, geometry, 3D
SYNOPSIS
v.hull
v.hull --help
v.hull [-rf] input=name [layer=string] output=name [cats=range]
[where=sql_query] [--overwrite] [--help] [--verbose] [--quiet]
[--ui]
Flags:
-r
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
--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
layer=string
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
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
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, un-
less the user specifies the -f flag. The 3D hull will be composed of
triangular faces.
Fig: Convex hull polygon created with v.hull
NOTES
In order to use the where option the layer option must be set to a pos-
itive number (the default is ’-1’ for ’all layers’), otherwise all
points from all layers will be used and the cats and where options will
be ignored.
EXAMPLE
Example of v.hull 3D output (using two random 3D point clouds, North
Carolina sample data set):
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
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)
Fig: Convex hull in 3D from 3D points created with v.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 Edi-
tion), chapter 4.
SEE ALSO
v.delaunay
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)
SOURCE CODE
Available at: v.hull source code (history)
Accessed: unknown
Main index | Vector index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 v.hull(1grass)
Generated by dwww version 1.14 on Sun Dec 29 19:29:46 CET 2024.