Ubuntu Manpage: r.clump - Recategorizes data in a raster map by grouping cells that form physically discrete areas into

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 ignored. 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
recategorize 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
increasing 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. Examples 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 direct 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 considered to be contiguous, but
       diagonal lines of cells are not considered 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 output raster map.

EXAMPLES

   Clumping of a raster map
       Perform clumping on "lakes" map (North Carolina sample dataset) and  report  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)

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: Friday Apr 04 01:19:02 2025

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       © 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual

GRASS 8.4.1                                                                                      r.clump(1grass)