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 inhab >= 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

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

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)

       Last changed: $Date: 2015-01-15 09:43:36 +0100 (Thu, 15 Jan 2015) $

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