
NAME
v.dissolve - Dissolve boundaries between adjacent areas sharing a common category number
KEYWORDS
vector, area
SYNOPSIS
v.dissolve
v.dissolve help
v.dissolve input=name output=name [layer=integer] [--overwrite] [--verbose] [--quiet]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- input=name
- Name of input vector map
- output=name
- Name for output vector map
- layer=integer
- Layer number. If -1, all layers are extracted
- Default: 1
DESCRIPTION
The v.dissolve module is used to merge adjacent areas in a vector
map which share the same category value. The resulting merged area(s) retains
this category value.
GRASS defines a vector area as composite entity consisting of a set of
closed boundaries and a centroid. The centroids must contain a category
number (see v.centroids), this number is linked to area
attributes and database links.
Multiple attributes may be linked to a single vector entity through
numbered fields referred to as layers.
Refer to v.category for more details.
Merging of areas can also be accomplished using "v.extract
-d" which provides some additional options.
In fact, v.dissolve is simply a front-end to that module.
(GRASS Shell Script)
EXAMPLES
Basic use
v.dissolve input=undissolved output=dissolved
Dissolving based on column attributes
# check column names:
v.info -c polbnda_italy
# reclass based on desired column:
v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam
# dissolve:
v.dissove input=polbnda_italy_recl_nam output=pol_italy_regions
Dissolving adjacent SHAPE files to remove tile boundaries
If tile boundaries of adjacent maps (e.g. CORINE Landcover SHAPE files)
have to be removed, an extra step is required to remove duplicated
boundaries:
# patch tiles after import:
v.patch -e `g.mlist type=vect pat="clc2000_*" sep=,` out=clc2000_patched
# remove duplicated tile boundaries:
v.clean clc2000_patched out=clc2000_clean tool=snap,break,rmdupl thresh=.01
# reclass based on desired column:
v.reclass clc2000_clean out=clc2000_recl col=CODE_00
# dissolve:
v.dissolve input=clc2000_recl output=clc2000_final
SEE ALSO
v.category,
v.centroids,
v.extract,
v.reclass
AUTHORS
module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
help page: Trevor Wiens
Last changed: $Date: 2006/11/19 20:02:56 $
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