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 4.5.11                                         5 Nov 2013                                        GMTDP(1gmt)