gmtdp(1) - f14

1GMTDP(1)                     Generic Mapping Tools                    GMTDP(1)
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NAME

6       gmtdp - Line reduction using the Douglas-Peucker algorithm
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SYNOPSIS

9       gmtdp  infiles  -Ttolerance  [  -H[i][nrec]  ]  [  -V  ]  [ -:[i|o] ] [
10       -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ]
11       [ -m[i|o][flag] ]
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DESCRIPTION

14       gmtdp  reads  one  or more data files (which may be multisegment files;
15       see -m) and apply the Douglas-Peucker  line  simplification  algorithm.
16       The  method  recursively subdivides a polygon until a run of points can
17       be replaced by a straight line segment, with no point in that run devi‐
18       ating  from  the straight line by more than the tolerance.  Have a look
19       at this site to get  a  visual  insight  on  how  the  algorithm  works
20       http://geometryalgorithms.com/Archive/algorithm_0205/algorithm_0205.htm
21       WARNING: currently this program should be used only  with  geographical
22       coordinates.
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24       file(s)
25              One  of more data files. If none are supplied then we read stan‐
26              dard input.
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OPTIONS

29       -T     Specifies the maximum mismatch tolerance in km.
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31       -H     Input file(s) has header record(s).  If used, the default number
32              of  header records is N_HEADER_RECS.  Use -Hi if only input data
33              should have  header  records  [Default  will  write  out  header
34              records  if  the  input  data  have them]. Blank lines and lines
35              starting with # are always skipped.
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37       -V     Selects verbose mode, which will send progress reports to stderr
38              [Default runs "silently"].
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40       -:     Toggles  between  (longitude,latitude)  and (latitude,longitude)
41              input and/or output.  [Default is (longitude,latitude)].  Append
42              i  to  select  input  only or o to select output only.  [Default
43              affects both].
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45       -bi    Selects binary input.  Append s for single precision [Default is
46              d  (double)].   Uppercase  S  or  D  will  force  byte-swapping.
47              Optionally, append ncol, the number of columns  in  your  binary
48              input  file if it exceeds the columns needed by the program.  Or
49              append c  if  the  input  file  is  netCDF.  Optionally,  append
50              var1/var2/...  to specify the variables to be read.  [Default is
51              2 input columns].
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53       -bo    Selects binary output.  Append s for single  precision  [Default
54              is  d  (double)].   Uppercase  S  or D will force byte-swapping.
55              Optionally, append ncol, the number of desired columns  in  your
56              binary output file.  [Default is same as input].
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58       -f     Special  formatting of input and/or output columns (time or geo‐
59              graphical data).  Specify i or o to  make  this  apply  only  to
60              input  or  output  [Default  applies to both].  Give one or more
61              columns (or column ranges) separated by commas.  Append T (abso‐
62              lute  calendar time), t (relative time in chosen TIME_UNIT since
63              TIME_EPOCH), x (longitude), y (latitude), or f (floating  point)
64              to  each  column or column range item.  Shorthand -f[i|o]g means
65              -f[i|o]0x,1y (geographic coordinates).
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67       -m     Multiple segment file(s).  Segments are separated by  a  special
68              record.   For  ASCII  files  the  first  character  must be flag
69              [Default is '>'].  For binary files all fields must be  NaN  and
70              -b must set the number of output columns explicitly.  By default
71              the -m setting applies to both input and output.   Use  -mi  and
72              -mo to give separate settings to input and output.
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ASCII FORMAT PRECISION

75       The ASCII output formats of numerical data are controlled by parameters
76       in your .gmtdefaults4  file.   Longitude  and  latitude  are  formatted
77       according  to  OUTPUT_DEGREE_FORMAT, whereas other values are formatted
78       according to D_FORMAT.  Be aware that the format in effect can lead  to
79       loss  of  precision  in  the output, which can lead to various problems
80       downstream.  If you find the output is not written with  enough  preci‐
81       sion, consider switching to binary output (-bo if available) or specify
82       more decimals using the D_FORMAT setting.
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EXAMPLE

85       To reduce the line segment.d using a tolerance of 2 km, run
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87       gmtdp segment.d -T2 > new_segment.d
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REFERENCES

91       Douglas, D. H., and T. K. Peucker, Algorithms for the reduction of  the
92       number  of points required to represent a digitized line of its carica‐
93       ture, Can. Cartogr., 10, 112-122, 1973.
94       This implementation of the algorithm has been kindly  provided  by  Dr.
95       Gary  J.  Robinson, Environmental Systems Science Centre, University of
96       Reading, Reading, UK (gazza@mail.nerc-essc.ac.uk); his subroutine forms
97       the basis for this program.
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