GRASS GIS: m.dispolygseg

NAME

m.dispolygseg - dissolving small areal entities (with hierarchical level) after segmentation

KEYWORDS

vector, selective dissolve, areal, hierarchical order

SYNOPSIS

m.dispolygseg
m.dispolygseg help
m.dispolygseg [-i] input=name output=name area=float [unit=string] [columnp=string] [valuep=string] [--overwrite] [--verbose] [--quiet]

Flags:

-i: print only statistics (no calcul) and exit
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

input=name: Input vector name
output=name: Output vector name
area=float: min area value
unit=string: units (meters (me), kilometers (k), acres(a), hectares(h)); Options: me,k,a,h; Default: me
columnp=string: Name of column used to treat particular entities (column must exist)
valuep=string: value used in 'columnp' to identify the particular entities

DESCRIPTION

m.dispolygseg allows the user to dissolve small areal entities with user's threshold (area parameter) and with hierarchical order. The input layer must be created by m.seg script. Flag i prints only statistics (see Examples for details). Columnp and valuep can be used to treat separately particular entities (e.g. road entities can be dissolved only with road entities), see Examples for details. To treat particular entities, m.colseg script must be used to patch attribute column to identify entities.

NOTES

Small areal entities are dissolved to the neighouring entity with whom they share the longest boundary and whom have the lowest hierarchical order (selective cleaning procedure). The hierarchical order is defined by m.seg script and is provided by the attribute table(s)s of the input vector data. The dissolving process is iterative (process is stopped when no more small entity is found). Small areal entities under threshold but with no neighbours are preserved.

EXAMPLES

Print statistics for dissolving areal entities for the seg1 vector map (threshold is 1200 square meters)

GRASS 6.3.0 :~ > m.dispolygseg -i input=seg1 output=seg2 area=1200 unit=me
You choose a minimum area of 1200 m2
 For the vector seg1,
 the dissolving small area entities operation will work
 on 6 polygons for 28 total polygons
 and will represent 4.3 % of the total surface

Dissolving areal entities

Dissolving areal entities for the seg1 vector map (threshold is 1200 square meters)

GRASS 6.3.0 :~ > m.dispolygseg input=seg1 output=seg2 area=1200 unit=me

Particular entities treatment

Dissolving small areal entities for the seg1 vector map (threshold is 1000 square meters) and separate treatment for particular entities defined by the column 'type' and the value 'road' Using m.colseg script to patch attribute column from field vector input data.

GRASS 6.3.0 :~ > m.colseg input=seg1 output=seg1p polygon=field columns=type
GRASS 6.3.0 :~ > m.dispolygseg input=seg1p output=seg2 area=1000 unit=me columnp=type valuep=road

AUTHORS

Michael Rabotin, UMR LISAH, Montpellier, France

rabotin@supagro.inra.fr

Last Changed: 21 July 2010

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