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<title>IMG2GRD</title>
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<h1 align=center>IMG2GRD</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="#EXAMPLES">EXAMPLES</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">img2grd −
Extract region of img in Mercator or geographic form</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>img2grd</b>
<i>imgfile</i> <b>−G</b><i>grdfile</i>
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
<b>−T</b><i>type</i> [ <b>−C</b> ] [
<b>−D</b>[<i>minlat/maxlat</i>] ] [ <b>−E</b> ]
[ <b>−L</b> ] [ <b>−M</b> ] [
<b>−N</b><i>navg</i> ] [ <b>−S</b><i>scale</i> ]
[ <b>−V</b> ] [ <b>−W</b><i>maxlon</i> ] [
<b>−m</b><i>minutes</i> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>img2grd</b>
is a front-end to <b><A HREF="img2mercgrd.html">img2mercgrd</A></b> which reads an img
format file and creates a grid file. The <b>−M</b>
option dictates whether or not the Spherical Mercator
projection of the img file is preserved. <i><br>
imgfile</i></p>
<p style="margin-left:22%;">An img format file such as the
marine gravity or seafloor topography fields estimated from
satellite altimeter data by Sandwell and Smith. If the user
has set an environment variable <b>$GMT_DATADIR</b>, then
<b><A HREF="img2mercgrd.html">img2mercgrd</A></b> will try to find <i>imgfile</i> in
<b>$GMT_DATADIR</b>; else it will try to open <i>imgfile</i>
directly.</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"><i>grdfile</i> is
the name of the output grid file.</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>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>type</i> handles
the encoding of constraint information. <i>type</i> = 0
indicates that no such information is encoded in the img
file (used for pre-1995 versions of the gravity data) and
gets all data. <i>type</i> > 0 indicates that constraint
information is encoded (1995 and later (current) versions of
the img files) so that one may produce a grid file as
follows: <b>−T</b><i>1</i> gets data values at all
points, <b>−T</b><i>2</i> gets data values at
constrained points and NaN at interpolated points;
<b>−T</b><i>3</i> gets 1 at constrained points and 0
at interpolated points.</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>−C</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Set the x and y
Mercator coordinates relative to projection center [Default
is relative to lower left corner of grid]. Requires
<b>−M</b>.</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="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Use the extended
latitude range -80.738/+80.738. Alternatively, append
<i>minlat/maxlat</i> as the latitude extent of the input img
file. [Default is -72.006/72.006].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Can be used when
<b>−M</b> is not set to force the final grid to have
the exact same region as requested with <b>−R</b>. By
default, the final region is a direct projection of the
original Mercator region and will typically extend slightly
beyond the requested latitude range, and furthermore the
grid increment in latitude does not match the longitude
increment. However, the extra resampling introduces small
interpolation errors and should only be used if the output
grid must match the requested region and have x_inc = y_inc.
In this case the region set by <b>−R</b> must be given
in multiples of the increment (.e.g, <b>−R</b>
0/45/45/72).</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">With no other
arguments, list all *.img files found in the directory
pointed to by <b>$GMT_DATADIR</b>, or the current directory
if not defined. Ignored if other options are present on the
command line.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−M</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Output a Spherical
Mercator grid [Default is a geographic lon/lat grid].</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="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Average the values
in the input img pixels into <i>navg</i> by <i>navg</i>
squares, and create one output pixel for each such square.
If used with <b>−T</b><i>3</i> it will report an
average constraint between 0 and 1. If used with
<b>−T</b><i>2</i> the output will be average data
value or NaN according to whether average constraint is >
0.5. <i>navg</i> must evenly divide into the dimensions of
the imgfile in pixels. [Default <i>1</i> does no
averaging].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Multiply the img
file values by <i>scale</i> before storing in grid file.
[Default is 1.0]. For recent img files: img topo files are
stored in (corrected) meters [<b>−S</b> 1]; free-air
gravity files in mGal*10 [<b>−S</b> 0.1 to get mGal];
vertical deflection files in microradians*10
[<b>−S</b> 0.1 to get microradians], vertical gravity
gradient files in Eotvos*50 [<b>−S</b> 0.02 to get
Eotvos, or <b>−S</b> 0.002 to get mGal/km]).</p></td>
<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"]. Particularly recommended here,
as it is helpful to see how the coordinates are
adjusted.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−m</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Indicate
<i>minutes</i> as the width of an input img pixel in minutes
of longitude. [Default is 2.0].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−W</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Indicate
<i>maxlon</i> as the maximum longitude extent of the input
img file. Versions since 1995 have had <i>maxlon</i> =
360.0, while some earlier files had <i>maxlon</i> = 390.0.
[Default is 360.0].</p></td>
</table>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To extract data
in the region <b>−R</b>-40/40/-70/-30 from
<i>world_grav.img.7.2</i> and preserve the Mercator
gridding:</p>
<p style="margin-left:11%; margin-top: 1em"><b>img2grd</b>
world_grav.img.7.2 <b>−G</b> merc_grav.grd
<b>−R</b>-40/40/-70/-30 <b>−M −T</b> 1
<b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">Without the
<b>−M</b> option the same command will yield a
geographic grid.</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="img2mercgrd.html">img2mercgrd</A></i>(1)</p>
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