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

Provided by: grass-doc_8.2.0-1build1_all

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: Mon Jun 13 15:09:14 2022

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