r.thin(1)

1r.thin(1)                     Grass User's Manual                    r.thin(1)
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NAME

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

10       raster
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SYNOPSIS

13       r.thin
14       r.thin help
15       r.thin  input=name  output=name   [iterations=integer]    [--overwrite]
16       [--verbose]  [--quiet]
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18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
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22       --verbose
23           Verbose module output
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25       --quiet
26           Quiet module output
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28   Parameters:
29       input=name
30           Name of input raster map
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32       output=name
33           Name for output raster map
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35       iterations=integer
36           Maximal number of iterations
37           Default: 200
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DESCRIPTION

40       r.thin  scans the named input raster map layer and thins non-zero cells
41       that denote linear features into linear features having a  single  cell
42       width.
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44       r.thin  will thin only the non-zero cells of the named input raster map
45       layer within the current geographic region settings.  The cell width of
46       the  thinned  output raster map layer will be equal to the cell resolu‐
47       tion of the currently set geographic region.  All of the thinned linear
48       features will have the width of a single cell.
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50       r.thin will create a new output raster data file containing the thinned
51       linear features.  r.thin assumes that linear features are encoded  with
52       positive values on a background of 0's in the input raster data file.
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NOTE

55       r.thin  only creates raster map layers.  You will need to run r.to.vect
56       on the resultant raster map to create a vector (v.digit) map layer.
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58       r.thin may create small spurs or "dangling lines" during  the  thinning
59       process.   These  spurs  may  be  removed  (after creating a vector map
60       layer) by v.clean.
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62       r.thin creates a 0/1 output map.
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NOTE

65       This code implements the thinning algorithm described in  "Analysis  of
66       Thinning Algorithms Using Mathematical Morphology" by Ben-Kwei Jang and
67       Ronlad T. Chin in Transactions on Pattern Analysis and Machine Intelli‐
68       gence, vol. 12, No. 6, June 1990.  The definition Jang and Chin give of
69       the thinning process is "successive removal of outer layers  of  pixels
70       from an object while retaining any pixels whose removal would alter the
71       connectivity or shorten the legs of the sceleton."
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73       The sceleton is finally thinned when the  thinning  process  converges;
74       i.e., "no further pixels can be removed without altering the connectiv‐
75       ity or shortening the sceleton legs" (p. 541).  The authors prove  that
76       the  thinning process described always converges and produces one-pixel
77       thick sceletons.  The number of  iterations  depends  on  the  original
78       thickness  of  the object.  Each iteration peels off the outside pixels
79       from the object.  Therefore, if the object is <= n  pixels  thick,  the
80       algorithm should converge in <= iterations.
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AUTHOR

86       Olga Waupotitsch, U.S.Army Construction Engineering Research Laboratory
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88       The  code for finding the bounding box as well as input/output code was
89       written by Mike Baba (DBA  Systems,  1990)  and  Jean  Ezell  (USACERL,
90       1988).
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92       Last changed: $Date: 2006-12-13 15:21:43 +0100 (Wed, 13 Dec 2006) $
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94       Full index
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96       © 2003-2008 GRASS Development Team
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100GRASS 6.3.0                                                          r.thin(1)