r.clump(1grass) GRASS GIS User's Manual r.clump(1grass)
NAME
r.clump - Recategorizes data in a raster map by grouping cells that
form physically discrete areas into unique categories.
KEYWORDS
raster, statistics, reclass, clumps
SYNOPSIS
r.clump
r.clump --help
r.clump [-dg] input=name[,name,...] [output=name] [title=string]
[threshold=float] [minsize=integer] [--overwrite] [--help]
[--verbose] [--quiet] [--ui]
Flags:
-d
Clump also diagonal cells
Clumps are also traced along diagonal neighboring cells
-g
Print only the number of clumps in shell script style
--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[,name,...] [required]
Name of input raster map(s)
output=name
Name for output raster map
title=string
Title for output raster map
threshold=float
Threshold to identify similar cells
Valid range: 0 = identical to < 1 = maximal difference
Default: 0
minsize=integer
Minimum clump size in cells
Clumps smaller than minsize will be merged to form larger clumps
Default: 1
DESCRIPTION
r.clump finds all areas of contiguous cell category values (connected
components) in the input raster map. NULL values in the input are ig-
nored. It assigns a unique category value to each such area ("clump")
in the resulting output raster map.
Category distinctions in the input raster map are preserved. This
means that if distinct category values are adjacent, they will NOT be
clumped together. The user can run r.reclass prior to r.clump to recat-
egorize cells and reassign cell category values.
r.clump can also perform "fuzzy" clumping where neighboring cells that
are not identical but similar to each other are clumped together. Here,
the spectral distance between two cells is scaled to the range [0, 1]
and compared to the threshold value. Cells are clumped together if
their spectral distance is ≤ threshold. The result is very sensitive to
this threshold value, a recommended start value is 0.01, then increas-
ing or decreasing this value according to the desired output. Once a
suitable threshold has been determined, noise can be reduced by merging
small clumps with the minsize option.
r.clump can also use multiple raster maps of any kind (CELL, FCELL,
DCELL) as input. In this case, the spectral distance between cells is
used to determine the similarity of two cells. This means that input
maps must be metric: the difference cell 1 - cell 2 must make sense.
Categorical maps, e.g. land cover, can not be used in this case. Exam-
ples for valid input maps are satellite imagery, vegetation indices,
elevation, climatic parameters etc.
NOTES
By default, the resulting clumps are connected only by their four di-
rect neighbors (left, right, top, bottom). The -d flag activates also
diagonal clump tracing.
r.clump works properly with raster map that contains only "fat" areas
(more than a single cell in width). Linear elements (lines that are a
single cell wide) may or may not be clumped together depending on the
direction of the line - horizontal and vertical lines of cells are con-
sidered to be contiguous, but diagonal lines of cells are not consid-
ered to be contiguous and are broken up into separate clumps unless the
-d flag is used.
A random color table and other support files are generated for the out-
put raster map.
EXAMPLES
Clumping of a raster map
Perform clumping on "lakes" map (North Carolina sample dataset) and re-
port area sizes for each lake individually rather by waterbody type:
g.region raster=lakes -p
# report sizes by waterbody type
r.report lakes units=h
# clump per raster polygon
r.clump lakes out=lakes_individual
# report sizes by individual waterbody
r.report lakes_individual units=h
Figure: Clumping of rasterized lakes: original lakes map (left) and
clumped lakes map (right)
Fuzzy clumping on Landsat bands
Perform fuzzy clumping on Landsat 7 2002 imagery (North Carolina sample
dataset)
g.region raster=lsat7_2002_10 -p
r.clump in=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70 \
out=lsat7_2002_clump threshold=0.045
# reduce noise
r.clump in=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70 \
out=lsat7_2002_clump_min10 threshold=0.045 minsize=10
Figure: Fuzzy clumping on Landsat bands: original RGB composite (left),
fuzzy clumped map (middle), and fuzzy clumped with minsize map (right)
SEE ALSO
r.average, r.buffer, r.distance, r.grow, r.mapcalc, r.mfilter,
r.neighbors, r.to.vect, r.reclass, r.statistics, r.support
AUTHORS
Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
Markus Metz (diagonal clump tracing, fuzzy clumping)
SOURCE CODE
Available at: r.clump source code (history)
Accessed: unknown
Main index | Raster index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 r.clump(1grass)
Generated by dwww version 1.14 on Sun Dec 29 18:56:20 CET 2024.