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<title>GMTDP</title>
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<h1 align="center">GMTDP</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#ASCII FORMAT PRECISION">ASCII FORMAT PRECISION</a><br>
<a href="#EXAMPLE">EXAMPLE</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">gmtdp −
Line reduction using the Douglas-Peucker algorithm</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>gmtdp</b>
<i>infiles</i> <b>−T</b><i>tolerance</i> [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [ <b>−V</b> ]
[ <b>−:</b>[<b>i</b>|<b>o</b>] ] [
<b>−b</b>[<b>i</b>|<b>o</b>][<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
] [
<b>−bo</b>[<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
] [ <b>−m</b>[<b>i</b>|<b>o</b>][<i>flag</i>] ]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>gmtdp</b>
reads one or more data files (which may be multisegment
files; see <b>−m</b>) 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. <i><br>
file(s)</i></p>
<p style="margin-left:22%;">One of more data files. If none
are supplied then we read standard input.</p>
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em"><b>−T</b></p></td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em">Specifies the maximum mismatch
tolerance in km.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−H</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Input file(s) has header record(s). If used, the default
number of header records is <b><A HREF="gmtdefaults.html#N_HEADER_RECS">N_HEADER_RECS</A></b>. Use
<b>−Hi</b> 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.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−V</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−:</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Toggles between (longitude,latitude) and
(latitude,longitude) input and/or output. [Default is
(longitude,latitude)]. Append <b>i</b> to select input only
or <b>o</b> to select output only. [Default affects
both].</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−bi</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects binary input. Append <b>s</b> for single
precision [Default is <b>d</b> (double)]. Uppercase <b>S</b>
or <b>D</b> will force byte-swapping. Optionally, append
<i>ncol</i>, the number of columns in your binary input file
if it exceeds the columns needed by the program. Or append
<b>c</b> if the input file is netCDF. Optionally, append
<i>var1</i><b>/</b><i>var2</i><b>/</b><i>...</i> to specify
the variables to be read. [Default is 2 input columns].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−bo</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects binary output. Append <b>s</b> for single
precision [Default is <b>d</b> (double)]. Uppercase <b>S</b>
or <b>D</b> will force byte-swapping. Optionally, append
<i>ncol</i>, the number of desired columns in your binary
output file. [Default is same as input].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−f</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Special formatting of input and/or output columns (time
or geographical data). Specify <b>i</b> or <b>o</b> 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 <b>T</b> (absolute calendar time),
<b>t</b> (relative time in chosen <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b> since
<b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>), <b>x</b> (longitude), <b>y</b>
(latitude), or <b>f</b> (floating point) to each column or
column range item. Shorthand
<b>−f</b>[<b>i</b>|<b>o</b>]<b>g</b> means
<b>−f</b>[<b>i</b>|<b>o</b>]0<b>x</b>,1<b>y</b>
(geographic coordinates).</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−m</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Multiple segment file(s). Segments are separated by a
special record. For ASCII files the first character must be
<i>flag</i> [Default is ’>’]. For binary
files all fields must be NaN and <b>−b</b> must set
the number of output columns explicitly. By default the
<b>−m</b> setting applies to both input and output.
Use <b>−mi</b> and <b>−mo</b> to give separate
settings to input and output.</p></td></tr>
</table>
<h2>ASCII FORMAT PRECISION
<a name="ASCII FORMAT PRECISION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The ASCII
output formats of numerical data are controlled by
parameters in your .gmtdefaults4 file. Longitude and
latitude are formatted according to
<b><A HREF="gmtdefaults.html#OUTPUT_DEGREE_FORMAT">OUTPUT_DEGREE_FORMAT</A></b>, whereas other values are
formatted according to <b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b>. 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 (<b>−bo</b> if
available) or specify more decimals using the
<b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b> setting.</p>
<h2>EXAMPLE
<a name="EXAMPLE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">To reduce the
line segment.d using a tolerance of 2 km, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>gmtdp</b>
segment.d <b>−T</b> 2 > new_segment.d</p>
<h2>REFERENCES
<a name="REFERENCES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">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, <i>Can. Cartogr., 10</i>, 112-122, 1973.
<br>
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.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</A></i>(1)</p>
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