v.hull.1grass - Man Page

Produces a 2D/3D convex hull for a given vector map.


vector, geometry, 3D


v.hull --help
v.hull [-rf] input=name  [layer=string]  output=name  [cats=range]   [where=sql_query]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]



Limit to current region


Create a ’flat’ 2D hull even if the input is 3D points


Allow output files to overwrite existing files


Print usage summary


Verbose module output


Quiet module output


Force launching GUI dialog


input=name [required]

Name of input vector map
Or data source for direct OGR access


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


Category values
Example: 1,3,7-9,13


WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and population >= 10000


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


In order to use the where option the layer option must be set to a positive 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 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


See Also



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: Tuesday Mar 19 11:02:17 2024

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