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<title>GRDLANDMASK</title>
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<h1 align=center>GRDLANDMASK</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="#EXAMPLES">EXAMPLES</a><br>
<a href="#GSHHS INFORMATION">GSHHS INFORMATION</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">grdlandmask
− Create "wet-dry" mask grid file from
shoreline data base.</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdlandmask
−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><i>min_area</i>[<i>/min_level/max_level</i>][<b>+r</b>|<b>l</b>][<b>p</b><i>percent</i>]
] [ <b>−D</b><i>resolution</i>[<b>+</b>] ] [
<b>−F</b> ] [
<b>−N</b><i>maskvalues</i>[<b>o</b>] ] [
<b>−V</b> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdlandmask</b>
reads the selected shoreline database and uses that
information to decide which nodes in the specified grid are
over land or over water. The nodes defined by the selected
region and lattice spacing will be set according to one of
two criteria: (1) land vs water, or (2) the more detailed
(hierarchical) ocean vs land vs lake vs island vs pond. The
resulting mask may be used in subsequent operations
involving <b><A HREF="grdmath.html">grdmath</A></b> to mask out data from land [or
water] areas.</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 style="margin-top: 1em" valign="top"><b>−G</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Name of resulting
output mask grid file. (See GRID FILE FORMATS below).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><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 valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>west, east,
south,</i> and <i>north</i> specify the Region of interest,
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.</p></td>
</table>
<a name="OPTIONS"></a>
<h2>OPTIONS</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="3%">
<p style="margin-top: 1em" valign="top"><b>−A</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Features with an
area smaller than <i>min_area</i> in km^2 or of hierarchical
level that is lower than <i>min_level</i> or higher than
<i>max_level</i> will not be plotted [Default is 0/0/4 (all
features)]. Level 2 (lakes) contains regular lakes and wide
river bodies which we normally include as lakes; append
<b>+r</b> to just get river-lakes or <b>+l</b> to just get
regular lakes (requires GSHHS 2.0.1 or higher). Finally,
append <b>+p</b><i>percent</i> to exclude polygons whose
percentage area of the corresponding full-resolution feature
is less than <i>percent</i> (requires GSHHS 2.0 or higher).
See GSHHS INFORMATION below for more details.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Selects the
resolution of the data set to use ((<b>f</b>)ull,
(<b>h</b>)igh, (<b>i</b>)ntermediate, (<b>l</b>)ow, or
(<b>c</b>)rude). The resolution drops off by ~80% between
data sets. [Default is <b>l</b>]. Append <b>+</b> to
automatically select a lower resolution should the one
requested not be available [abort if not found]. Note that
because the coastlines differ in details a node in a mask
file using one resolution is not guaranteed to remain inside
[or outside] when a different resolution is selected.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−F</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Sets the values
that will be assigned to nodes. Values can be any number,
including the textstring NaN. Append <b>o</b> to let nodes
exactly on feature boundaries be considered outside [Default
is inside]. Specify this information using 1 of 2
formats:</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>−N</b><i>wet/dry</i>.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>−N</b><i>ocean/land/lake/island/pond</i>.</p> </td>
</table>
<p style="margin-left:22%;">[Default is 0/1/0/1/0 (i.e.,
0/1)].</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 style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
</table>
<a name="GRID FILE FORMATS"></a>
<h2>GRID FILE FORMATS</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>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To set all
nodes on land to NaN, and nodes over water to 1, using the
high resolution data set, do</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdlandmask
−R</b>-60/-40/-40/-30 <b>−Dh −i</b>5<b>m
−N</b>1/NaN <b>−G</b>land_mask.grd
<b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To make a 1x1
degree global grid with the hierarchical levels of the nodes
based on the low resolution data:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdlandmask
−R</b>0/360/-90/90 <b>−Dl −I</b>1
<b>−N</b>0/1/2/3/4 <b>−G</b>levels.grd
<b>−V</b></p>
<a name="GSHHS INFORMATION"></a>
<h2>GSHHS INFORMATION</h2>
<p style="margin-left:11%; margin-top: 1em">The coastline
database is GSHHS which is compiled from two sources: World
Vector Shorelines (WVS) and CIA World Data Bank II (WDBII).
In particular, all level-1 polygons (ocean-land boundary)
are derived from the more accurate WVS while all higher
level polygons (level 2-4, representing land/lake,
lake/island-in-lake, and
island-in-lake/lake-in-island-in-lake boundaries) are taken
from WDBII. Much processing has taken place to convert WVS
and WDBII data into usable form for <b><A HREF="GMT.html">GMT</A></b>: assembling
closed polygons from line segments, checking for duplicates,
and correcting for crossings between polygons. The area of
each polygon has been determined so that the user may choose
not to draw features smaller than a minimum area (see
<b>−A</b>); one may also limit the highest
hierarchical level of polygons to be included (4 is the
maximum). The 4 lower-resolution databases were derived from
the full resolution database using the Douglas-Peucker
line-simplification algorithm. The classification of rivers
and borders follow that of the WDBII. See the <b><A HREF="GMT.html">GMT</A></b>
Cookbook and Technical Reference Appendix K for further
details.</p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</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), <i><A HREF="pscoast.html">pscoast</A></i>(1)</p>
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