NAME

       gmtdp - Line reduction using the Douglas-Peucker algorithm

SYNOPSIS

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

DESCRIPTION

       gmtdp reads one or more data files (which may be multisegment files; see -m) and apply the
       Douglas-Peucker line simplification algorithm. The method recursively subdivides a polygon
       until a run of points can be replaced by a straight line segment, with no  point  in  that
       run deviating from the straight line by more than the tolerance.  Have a look at this site
       to     get     a     visual     insight     on      how      the      algorithm      works
       http://geometryalgorithms.com/Archive/algorithm_0205/algorithm_0205.htm WARNING: currently
       this program should be used only with geographical coordinates.

       file(s)
              One of more data files. If none are supplied then we read standard input.

OPTIONS

       -T     Specifies the maximum mismatch tolerance in km.

       -H     Input file(s) has header record(s).  If used, the default number of header  records
              is  N_HEADER_RECS.   Use -Hi if only input data should have header records [Default
              will write out header records if the input data have them]. Blank lines  and  lines
              starting with # are always skipped.

       -V     Selects  verbose  mode,  which  will  send progress reports to stderr [Default runs
              "silently"].

       -:     Toggles between (longitude,latitude) and (latitude,longitude) input and/or  output.
              [Default  is  (longitude,latitude)].   Append i to select input only or o to select
              output only.  [Default affects both].

       -bi    Selects binary input.  Append s for  single  precision  [Default  is  d  (double)].
              Uppercase  S or D will force byte-swapping.  Optionally, append ncol, the number of
              columns in your binary input file if it exceeds the columns needed by the  program.
              Or  append  c  if  the  input  file  is netCDF. Optionally, append var1/var2/... to
              specify the variables to be read.  [Default is 2 input columns].

       -bo    Selects binary output.  Append s for single  precision  [Default  is  d  (double)].
              Uppercase  S or D will force byte-swapping.  Optionally, append ncol, the number of
              desired columns in your binary output file.  [Default is same as input].

       -f     Special formatting of input and/or output  columns  (time  or  geographical  data).
              Specify  i  or  o  to  make  this apply only to input or output [Default applies to
              both].  Give one or more columns (or column ranges) separated by commas.  Append  T
              (absolute calendar time), t (relative time in chosen TIME_UNIT since TIME_EPOCH), x
              (longitude), y (latitude), or f (floating point) to each  column  or  column  range
              item.  Shorthand -f[i|o]g means -f[i|o]0x,1y (geographic coordinates).

       -m     Multiple  segment  file(s).  Segments are separated by a special record.  For ASCII
              files the first character must be flag [Default is  '>'].   For  binary  files  all
              fields  must  be  NaN  and -b must set the number of output columns explicitly.  By
              default the -m setting applies to both input and output.  Use -mi and -mo  to  give
              separate settings to input and output.

ASCII FORMAT PRECISION

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

EXAMPLE

       To reduce the line segment.d using a tolerance of 2 km, run

       gmtdp segment.d -T 2 > new_segment.d

REFERENCES

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

SEE ALSO

       GMT(1)