1v.hull(1) Grass User's Manual v.hull(1)
2
3
4
6 v.hull - Produces a 2D/3D convex hull for a given vector map.
7
9 vector, geometry, 3D
10
12 v.hull
13 v.hull --help
14 v.hull [-rf] input=name [layer=string] output=name [cats=range]
15 [where=sql_query] [--overwrite] [--help] [--verbose] [--quiet]
16 [--ui]
17
18 Flags:
19 -r
20 Limit to current region
21
22 -f
23 Create a ’flat’ 2D hull even if the input is 3D points
24
25 --overwrite
26 Allow output files to overwrite existing files
27
28 --help
29 Print usage summary
30
31 --verbose
32 Verbose module output
33
34 --quiet
35 Quiet module output
36
37 --ui
38 Force launching GUI dialog
39
40 Parameters:
41 input=name [required]
42 Name of input vector map
43 Or data source for direct OGR access
44
45 layer=string
46 Layer number or name (’-1’ for all layers)
47 A single vector map can be connected to multiple database tables.
48 This number determines which table to use. When used with direct
49 OGR access this is the layer name.
50 Default: -1
51
52 output=name [required]
53 Name for output vector map
54
55 cats=range
56 Category values
57 Example: 1,3,7-9,13
58
59 where=sql_query
60 WHERE conditions of SQL statement without ’where’ keyword
61 Example: income < 1000 and population >= 10000
62
64 v.hull computes the convex hull of a vector map and outputs the convex
65 hull polygon as a vector area map. The convex hull, or convex envelope,
66 for an object or a set of objects is the minimal convex set containing
67 the given objects. This module creates a vector polygon containing all
68 vector points or lines of the input map.
69
70 In the case of 3D input points, the hull will be a 3D hull as well,
71 unless the user specifies the -f flag. The 3D hull will be composed of
72 triangular faces.
73 Fig: Convex hull polygon created with v.hull
74
76 In order to use the where option the layer option must be set to a pos‐
77 itive number (the default is ’-1’ for ’all layers’), otherwise all
78 points from all layers will be used and the cats and where options will
79 be ignored.
80
82 Example of v.hull 3D output (using two random 3D point clouds, North
83 Carolina sample data set):
84 g.region rural_1m -p
85 r.mapcalc "zero = 0"
86 v.random -z output=random3d_a n=10 zmin=0 zmax=200
87 v.random -z output=random3d_b n=15 zmin=400 zmax=600
88 v.hull input=random3d_a output=random3d_a_hull
89 v.hull input=random3d_b output=random3d_b_hull
90 d.mon wx0
91 d.vect random3d_a_hull
92 d.vect random3d_a color=red
93 d.vect random3d_b_hull
94 d.vect random3d_b color=red
95 # 3D view in wxGUI (g.gui)
96 Fig: Convex hull in 3D from 3D points created with v.hull
97
99 · M. de Berg, M. van Kreveld, M. Overmars, O. Schwarzkopf,
100 (2000). Computational geometry, chapter 1.1, 2-8.
101
102 · J. O’Rourke, (1998). Computational Geometry in C (Second Edi‐
103 tion), chapter 4.
104
106 v.delaunay
107
109 Andrea Aime, Modena, Italy
110 Markus Neteler, ITC-irst (update to 5.7)
111 Benjamin Ducke, CAU Kiel (3D hull support)
112 Martin Landa, CTU in Prague, Czech Republic (vector lines support)
113
115 Available at: v.hull source code (history)
116
117 Main index | Vector index | Topics index | Keywords index | Graphical
118 index | Full index
119
120 © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
121
122
123
124GRASS 7.8.2 v.hull(1)