trusty (1) r.thin.1grass.gz

NAME

       r.thin  - Thins non-zero cells that denote linear features in a raster map.

KEYWORDS

       raster, thin

SYNOPSIS

       r.thin
       r.thin help
       r.thin input=name output=name  [iterations=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 raster map

       output=name
           Name for output raster map

       iterations=integer
           Maximal number of iterations
           Default: 200

DESCRIPTION

       r.thin  scans  the named input raster map layer and thins non-zero cells that denote linear features into
       linear features having a single cell width.

       r.thin will thin only the non-zero cells  of  the  named  input  raster  map  layer  within  the  current
       geographic  region  settings.  The cell width of the thinned output raster map layer will be equal to the
       cell resolution of the currently set geographic region.  All of the thinned linear features will have the
       width of a single cell.

       r.thin  will create a new output raster data file containing the thinned linear features.  r.thin assumes
       that linear features are encoded with positive values on a background of 0's in  the  input  raster  data
       file.

NOTE

       r.thin  only  creates  raster  map layers.  You will need to run r.to.vect on the resultant raster map to
       create a vector (v.digit) map layer.

       r.thin may create small spurs or "dangling lines" during  the  thinning  process.   These  spurs  may  be
       removed (after creating a vector map layer) by v.clean.

       r.thin creates a 0/1 output map.

NOTE

       This  code  implements  the  thinning  algorithm  described  in  "Analysis  of  Thinning Algorithms Using
       Mathematical Morphology" by Ben-Kwei Jang and Ronlad T. Chin in  Transactions  on  Pattern  Analysis  and
       Machine  Intelligence,  vol.  12,  No.  6,  June 1990.  The definition Jang and Chin give of the thinning
       process is "successive removal of outer layers of pixels from an object while retaining any pixels  whose
       removal would alter the connectivity or shorten the legs of the sceleton."

       The  sceleton  is  finally  thinned  when the thinning process converges; i.e., "no further pixels can be
       removed without altering the connectivity or shortening the sceleton legs" (p. 541).  The  authors  prove
       that  the thinning process described always converges and produces one-pixel thick sceletons.  The number
       of iterations depends on the original thickness of the object.  Each  iteration  peels  off  the  outside
       pixels  from the object.  Therefore, if the object is <= n pixels thick, the algorithm should converge in
       <= iterations.

SEE ALSO

       g.region, r.to.vect, v.clean, v.digit, v.build

AUTHOR

       Olga Waupotitsch, U.S.Army Construction Engineering Research Laboratory

       The code for finding the bounding box as well as input/output code was written by Mike Baba (DBA Systems,
       1990) and Jean Ezell (USACERL, 1988).

       Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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