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<title>GRDMASK</title>
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<h1 align="center">GRDMASK</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="#GRID FILE FORMATS">GRID FILE FORMATS</a><br>
<a href="#GEOGRAPHICAL AND TIME COORDINATES">GEOGRAPHICAL AND TIME COORDINATES</a><br>
<a href="#EXAMPLES">EXAMPLES</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">grdmask −
Create mask grid files from xy paths.</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdmask</b>
<i>pathfiles</i> <b>−G</b><i>mask_grd_file</i>]
<b>−I</b><i>xinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>][/<i>yinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>]]
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
[ <b>−A</b>[<b>m</b>|<b>p</b>] ] [ <b>−F</b> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−N</b><i>out/edge/in</i> ] [
<b>−S</b><i>search_radius</i>[<b>m|c|k|K</b>] ] [
<b>−V</b> ] [ <b>−:</b>[<b>i</b>|<b>o</b>] ] [
<b>−bi</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>−f</b><i>colinfo</i> ] [
<b>−m</b>[<i>flag</i>] ]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdmask</b>
can operate in two different modes. 1. It reads one or more
xy-files that each define a closed polygon. The nodes
defined by the specified region and lattice spacing will be
set equal to one of three possible values depending on
whether the node is outside, on the polygon perimeter, or
inside the polygon. The resulting mask may be used in
subsequent operations involving <b><A HREF="grdmath.html">grdmath</A></b> to mask out
data from polygonal areas. 2. The xy-files simply represent
data point locations and the mask is set to the inside or
outside value depending on whether a node is within a
maximum distance from the nearest data point. If the
distance specified is zero then only the nodes nearest each
data point are considered "inside". <i><br>
pathfiles</i></p>
<p style="margin-left:22%;">The name of 1 or more ASCII [or
binary, see <b>−b</b>] files holding the polygon(s) or
data points.</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−G</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Name of resulting output mask grid file. (See GRID FILE
FORMATS below).</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−I</b></p></td>
<td width="8%"></td>
<td width="78%">
<p><i>x_inc</i> [and optionally <i>y_inc</i>] is the grid
spacing. Optionally, append a suffix modifier.
<b>Geographical (degrees) coordinates</b>: Append <b>m</b>
to indicate arc minutes or <b>c</b> to indicate arc seconds.
If one of the units <b>e</b>, <b>k</b>, <b>i</b>, or
<b>n</b> is appended instead, the increment is assumed to be
given in meter, km, miles, or nautical miles, respectively,
and will be converted to the equivalent degrees longitude at
the middle latitude of the region (the conversion depends on
<b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b>). If /<i>y_inc</i> is given but set to 0 it
will be reset equal to <i>x_inc</i>; otherwise it will be
converted to degrees latitude. <b>All coordinates</b>: If
<b>=</b> is appended then the corresponding max <i>x</i>
(<i>east</i>) or <i>y</i> (<i>north</i>) may be slightly
adjusted to fit exactly the given increment [by default the
increment may be adjusted slightly to fit the given domain].
Finally, instead of giving an increment you may specify the
<i>number of nodes</i> desired by appending <b>+</b> to the
supplied integer argument; the increment is then
recalculated from the number of nodes and the domain. The
resulting increment value depends on whether you have
selected a gridline-registered or pixel-registered grid; see
Appendix B for details. Note: if
<b>−R</b><i>grdfile</i> is used then grid spacing has
already been initialized; use <b>−I</b> to override
the values.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−R</b></p></td>
<td width="8%"></td>
<td width="78%">
<p><i>xmin</i>, <i>xmax</i>, <i>ymin</i>, and <i>ymax</i>
specify the Region of interest. For geographic regions,
these limits correspond to <i>west, east, south,</i> and
<i>north</i> and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if
lower left and upper right map coordinates are given instead
of w/e/s/n. The two shorthands <b>−Rg</b> and
<b>−Rd</b> stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in
latitude). Alternatively, specify the name of an existing
grid file and the <b>−R</b> settings (and grid
spacing, if applicable) are copied from the grid. For
calendar time coordinates you may either give (a) relative
time (relative to the selected <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and in the
selected <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>; append <b>t</b> to
<b>−JX</b>|<b>x</b>), or (b) absolute time of the form
[<i>date</i>]<b>T</b>[<i>clock</i>] (append <b>T</b> to
<b>−JX</b>|<b>x</b>). At least one of <i>date</i> and
<i>clock</i> must be present; the <b>T</b> is always
required. The <i>date</i> string must be of the form
[-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
(ISO week calendar), while the <i>clock</i> string must be
of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be exactly as indicated (however,
input, output and plot formats are customizable; see
<b><A HREF="gmtdefaults.html">gmtdefaults</A></b>).</p> </td></tr>
</table>
<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>−A</b></p></td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em">If the input data are geographic
(as indicated by <b>−fi</b>) then the sides in the
polygons will be approximated by great circle arcs. When
using the <b>−A</b> sides will be regarded as straight
lines. Alternatively, append <b>m</b> to have sides first
follow meridians, then parallels. Or append <b>p to first
follow parallels, then meridians.</b></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>Force pixel node registration [Default is gridline
registration]. (Node registrations are defined in <b><A HREF="GMT.html">GMT</A></b>
Cookbook Appendix B on grid file formats.)</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>−N</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Sets the values that will be assigned to nodes that are
<i>out</i>side the polygons, on the <i>edge</i>, or
<i>in</i>side. Values can be any number, including the
textstring NaN [Default is 0/0/1].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−S</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Set nodes depending on their distance from the nearest
data point. Nodes within <i>radius</i> [0] from a data point
are considered inside. Append <b>m</b> to indicate minutes
or <b>c</b> to indicate seconds. Append <b>k</b> to indicate
km (implies <b>−R</b> and <b>−I</b> are in
degrees, and we will use a fast flat Earth approximation to
calculate distance). For more accuracy, use uppercase
<b>K</b> if distances should be calculated along geodesics.
However, if the current <b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b> is spherical then
great circle calculations are used. If <b>−S</b> is
not set then we consider the input data to define closed
polygon(s) instead.</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>−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>−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. Segments are separated by a
record whose first character is <i>flag</i>. [Default is
’>’].</p> </td></tr>
</table>
<h2>GRID FILE FORMATS
<a name="GRID FILE FORMATS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">By default
<b><A HREF="GMT.html">GMT</A></b> writes out grid as single precision floats in a
COARDS-complaint netCDF file format. However, <b><A HREF="GMT.html">GMT</A></b> is
able to produce grid files in many other commonly used grid
file formats and also facilitates so called
"packing" of grids, writing out floating point
data as 2- or 4-byte integers. To specify the precision,
scale and offset, the user should add the suffix
<b>=</b><i>id</i>[<b>/</b><i>scale</i><b>/</b><i>offset</i>[<b>/</b><i>nan</i>]],
where <i>id</i> is a two-letter identifier of the grid type
and precision, and <i>scale</i> and <i>offset</i> are
optional scale factor and offset to be applied to all grid
values, and <i>nan</i> is the value used to indicate missing
data. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and Section 4.17 of the GMT
Technical Reference and Cookbook for more information.</p>
<p style="margin-left:11%; margin-top: 1em">When writing a
netCDF file, the grid is stored by default with the variable
name "z". To specify another variable name
<i>varname</i>, append <b>?</b><i>varname</i> to the file
name. Note that you may need to escape the special meaning
of <b>?</b> in your shell program by putting a backslash in
front of it, or by placing the filename and suffix between
quotes or double quotes.</p>
<h2>GEOGRAPHICAL AND TIME COORDINATES
<a name="GEOGRAPHICAL AND TIME COORDINATES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">When the output
grid type is netCDF, the coordinates will be labeled
"longitude", "latitude", or
"time" based on the attributes of the input data
or grid (if any) or on the <b>−f</b> or
<b>−R</b> options. For example, both <b>−f0x
−f1t</b> and <b>−R</b> 90w/90e/0t/3t will result
in a longitude/time grid. When the x, y, or z coordinate is
time, it will be stored in the grid as relative time since
epoch as specified by <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b> and <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>
in the .gmtdefaults file or on the command line. In
addition, the <b>unit</b> attribute of the time variable
will indicate both this unit and epoch.</p>
<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">To set all
nodes inside and on the polygons coastline_*.xy to 0, and
outside points to 1, do</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdmask</b>
coastline_*.xy <b>−R</b>-60/-40/-40/-30
<b>−I</b> 5<b>m −N</b> 1/0/0 <b>−G</b>
land_mask.grd <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To set nodes
within 50 km of data points to 1 and other nodes to NaN,
do</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdmask</b>
data.xyz <b>−R</b>-60/-40/-40/-30 <b>−I</b>
5<b>m −N</b> NaN/1/1 <b>−S</b> 50<b>k
−G</b> data_mask.grd <b>−V</b></p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b><i><A HREF="GMT.html">GMT</A></i></b>(1),
<i><A HREF="grdlandmask.html">grdlandmask</A></i>(1), <i><A HREF="grdmath.html">grdmath</A></i>(1), <i><A HREF="grdclip.html">grdclip</A></i>(1),
<i><A HREF="psmask.html">psmask</A></i>(1), <i><A HREF="psclip.html">psclip</A></i>(1)</p>
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