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, unless 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  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

       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 Edition), chapter 4.

SEE ALSO

        v.delaunay

AUTHORS

       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: Thursday Aug 01 11:31:01 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.4.0 Reference Manual