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GMTDP(1)                     Generic Mapping Tools                    GMTDP(1)

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)

GMT 4.5.14                        1 Nov 2015                          GMTDP(1)