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<h1 align="center">GRDPROJECT</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="#RESTRICTIONS">RESTRICTIONS</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">grdproject
− Forward and Inverse map transformation of 2-D grid
files</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdproject</b>
<i>in_grdfile</i> <b>−G</b><i>out_grdfile</i>
<b>−J</b><i>parameters</i> [
<b>−A</b>[<b>k|m|n|i|c|p</b>] ] [
<b>−C</b>[<i>dx/dy</i>] ] [
<b>−D</b><i>xinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>][/<i>yinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>]]
] [ <b>−E</b><i>dpi</i> ] [ <b>−F</b> ] [
<b>−I</b> ] [
<b>−Mc</b>|<b>i</b>|<b>m</b>|<b>p</b> ] [
<b>−N</b><i>nx/ny</i> ] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [
<b>−S</b>[<b>-</b>]<b>b</b>|<b>c</b>|<b>l</b>|<b>n</b>[<b>/</b><i>threshold</i>]
] [ <b>−V</b> ]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdproject</b>
will do one of two things depending whether <b>−I</b>
has been set. If set, it will transform a gridded data set
from a rectangular coordinate system onto a geographical
system by resampling the surface at the new nodes. If not
set, it will project a geographical gridded data set onto a
rectangular grid. To obtain the value at each new node, its
location is inversely projected back onto the input grid
after which a value is interpolated between the surrounding
input grid values. By default bi-cubic interpolation is
used. Aliasing is avoided by also forward projecting the
input grid nodes. If two or more nodes are projected onto
the same new node, their average will dominate in the
calculation of the new node value. Interpolation and
aliasing is controlled with the <b>−S</b> option. The
new node spacing may be determined in one of several ways by
specifying the grid spacing, number of nodes, or resolution.
Nodes not constrained by input data are set to NaN. <br>
The <b>−R</b> option can be used to select a map
region larger or smaller than that implied by the extent of
the grid file. <i><br>
in_grdfile</i></p>
<p style="margin-left:22%;">2-D binary grid file to be
transformed. (See GRID FILE FORMATS below.)</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>Specify the name of the output grid file. (See GRID FILE
FORMATS below.)</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−J</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Selects the map projection. Scale is UNIT/degree,
1:xxxxx, or width in UNIT (upper case modifier). UNIT is cm,
inch, or m, depending on the <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> setting in
.gmtdefaults4, but this can be overridden on the command
line by appending <b>c</b>, <b>i</b>, or <b>m</b> to the
scale/width value. When central meridian is optional,
default is center of longitude range on <b>−R</b>
option. Default standard parallel is the equator. For map
height, max dimension, or min dimension, append <b>h</b>,
<b>+</b>, or <b>-</b> to the width, respectively.</p></td></tr>
</table>
<p style="margin-left:22%;">More details can be found in
the <b><A HREF="psbasemap.html">psbasemap</A></b> man pages.</p>
<p style="margin-left:22%; margin-top: 1em"><b>CYLINDRICAL
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Jc</b><i>lon0/lat0/scale</i>
(Cassini) <b><br>
−Jcyl_stere</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Stereographic) <b><br>
−Jj</b>[<i>lon0/</i>]<i>scale</i> (Miller) <b><br>
−Jm</b>[<i>lon0</i>/[<i>lat0/</i>]]<i>scale</i>
(Mercator) <b><br>
−Jm</b><i>lon0/lat0/scale</i> (Mercator - Give
meridian and standard parallel) <b><br>
−Jo</b>[<b>a</b>]<i>lon0/lat0/azimuth/scale</i>
(Oblique Mercator - point and azimuth) <b><br>
−Jo</b>[<b>b</b>]<i>lon0/lat0/lon1/lat1/scale</i>
(Oblique Mercator - two points) <b><br>
−Joc</b><i>lon0/lat0/lonp/latp/scale</i> (Oblique
Mercator - point and pole) <b><br>
−Jq</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Equidistant) <b><br>
−Jt</b><i>lon0/</i>[<i>lat0/</i>]<i>scale</i> (TM -
Transverse Mercator) <b><br>
−Ju</b><i>zone/scale</i> (UTM - Universal Transverse
Mercator) <b><br>
−Jy</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Equal-Area)</p>
<p style="margin-left:22%; margin-top: 1em"><b>CONIC
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Jb</b><i>lon0/lat0/lat1/lat2/scale</i>
(Albers) <b><br>
−Jd</b><i>lon0/lat0/lat1/lat2/scale</i> (Conic
Equidistant) <b><br>
−Jl</b><i>lon0/lat0/lat1/lat2/scale</i> (Lambert Conic
Conformal) <b><br>
−Jpoly</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
((American) Polyconic)</p>
<p style="margin-left:22%; margin-top: 1em"><b>AZIMUTHAL
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Ja</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Lambert Azimuthal Equal-Area) <b><br>
−Je</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Azimuthal Equidistant) <b><br>
−Jf</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Gnomonic) <b><br>
−Jg</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Orthographic) <b><br>
−Jg</b><i>lon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale</i>
(General Perspective). <b><br>
−Js</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(General Stereographic)</p>
<p style="margin-left:22%; margin-top: 1em"><b>MISCELLANEOUS
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Jh</b>[<i>lon0/</i>]<i>scale</i>
(Hammer) <b><br>
−Ji</b>[<i>lon0/</i>]<i>scale</i> (Sinusoidal) <b><br>
−Jkf</b>[<i>lon0/</i>]<i>scale</i> (Eckert IV) <b><br>
−Jk</b>[<b>s</b>][<i>lon0/</i>]<i>scale</i> (Eckert
VI) <b><br>
−Jn</b>[<i>lon0/</i>]<i>scale</i> (Robinson) <b><br>
−Jr</b>[<i>lon0/</i>]<i>scale</i> (Winkel Tripel)
<b><br>
−Jv</b>[<i>lon0/</i>]<i>scale</i> (Van der Grinten)
<b><br>
−Jw</b>[<i>lon0/</i>]<i>scale</i> (Mollweide)</p>
<p style="margin-left:22%; margin-top: 1em"><b>NON-GEOGRAPHICAL
PROJECTIONS:</b></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Jp</b>[<b>a</b>]<i>scale</i>[<i>/origin</i>][<b>r</b>|<b>z</b>]
(Polar coordinates (theta,r)) <b><br>
−Jx</b><i>x-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>][<i>/y-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>]]
(Linear, log, and power scaling)</p>
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments.</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"><b>−A</b></p></td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em">Force 1:1 scaling, i.e., output
(or input, see <b>−I</b>) data are in actual projected
meters. To specify other units, append <b>k</b> (km),
<b>m</b> (mile),<b>n</b> (nautical mile), <b>i</b> (inch),
<b>c</b> (cm), or <b>p</b> (points). Without
<b>−A</b>, the output (or input, see <b>−I</b>)
are in the units specified by <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> (but see
<b>−M</b>).</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−C</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Let projected coordinates be relative to projection
center [Default is relative to lower left corner].
Optionally, add offsets in the projected units to be added
(or subtracted when <b>−I</b> is set) to (from) the
projected coordinates, such as false eastings and northings
for particular projection zones [0/0].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−D</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>−D</b> to override
the values.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−E</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Set the resolution for the new grid in dots per
inch.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−F</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Toggle between pixel and gridline node registration
[Default is same as input].</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>Do the Inverse transformation, from rectangular to
geographical.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−M</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Append <b>c</b>, <b>i</b>, or <b>m</b> to indicate that
cm, inch, or meter should be the projected measure unit
[Default is set by <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> in .gmtdefaults4].
Cannot be used with <b>−A</b>.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−N</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Set the number of grid nodes in the new grid.</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>). You may ask to project only a subset of
the grid by specifying a smaller input <i>w/e/s/n</i> region
[Default is the region given by the grid file]. Special case
for the UTM projection: If <b>−C</b> and
<b>−I</b> are used and <b>−R</b> is not given
then the region is set to coincide with the given UTM zone
so as to preserve the full ellipsoidal solution (See
RESTRICTIONS for more information).</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−S</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Select the interpolation mode by adding <b>b</b> for
B-spline smoothing, <b>c</b> for bicubic interpolation,
<b>l</b> for bilinear interpolation, or <b>n</b> for
nearest-neighbor value (for example to plot categorical
data). Optionally, prepend <b>-</b> to switch off
antialiasing. Add <b>/</b><i>threshold</i> to control how
close to nodes with NaNs the interpolation will go. A
<i>threshold</i> of 1.0 requires all (4 or 16) nodes
involved in interpolation to be non-NaN. 0.5 will
interpolate about half way from a non-NaN value; 0.1 will go
about 90% of the way, etc. [Default is bicubic interpolation
with antialiasing and a threshold of 0.5].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>−V</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].</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. When reading grids, the format is generally
automatically recognized. If not, the same suffix can be
added to input grid file names. 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 reading a
netCDF file that contains multiple grids, <b><A HREF="GMT.html">GMT</A></b> will
read, by default, the first 2-dimensional grid that can find
in that file. To coax <b><A HREF="GMT.html">GMT</A></b> into reading another
multi-dimensional variable in the grid file, append
<b>?</b><i>varname</i> to the file name, where
<i>varname</i> is the name of the variable. 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. The <b>?</b><i>varname</i> suffix can also be used
for output grids to specify a variable name different from
the default: "z". See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and
Section 4.18 of the GMT Technical Reference and Cookbook for
more information, particularly on how to read splices of 3-,
4-, or 5-dimensional grids.</p>
<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">To transform
the geographical grid dbdb5.grd onto a pixel Mercator grid
at 300 dpi, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdproject</b>
dbdb5.grd <b>−R</b> 20/50/12/25 <b>−Jm</b>
0.25<b>i −E</b> 300 <b>−F −G</b>
dbdb5_merc.grd</p>
<p style="margin-left:11%; margin-top: 1em">To inversely
transform the file topo_tm.grd back onto a geographical
grid, use</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdproject</b>
topo_tm.grd <b>−R</b>-80/-70/20/40
<b>−Jt</b>-75/1:500000 <b>−I −D</b> 5<b>m
−V −G</b> topo.grd</p>
<p style="margin-left:11%; margin-top: 1em">This assumes,
of course, that the coordinates in topo_tm.grd were created
with the same projection parameters. <br>
To inversely transform the file topo_utm.grd (which is in
UTM meters) back to a geographical grid we specify a
one-to-one mapping with meter as the measure unit:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdproject</b>
topo_utm.grd <b>−R</b> 203/205/60/65 <b>−Ju</b>
5/1:1 <b>−I −Mm −G</b> topo.grd
<b>−V</b></p>
<h2>RESTRICTIONS
<a name="RESTRICTIONS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The boundaries
of a projected (rectangular) data set will not necessarily
give rectangular geographical boundaries (Mercator is one
exception). In those cases some nodes may be unconstrained
(set to NaN). To get a full grid back, your input grid may
have to cover a larger area than you are interested in. <br>
For some projections, a spherical solution may be used
despite the user having selected an ellipsoid. This occurs
when the users <b>−R</b> setting implies a region that
exceeds the domain in which the ellipsoidal series
expansions are valid. These are the conditions: (1) Lambert
Conformal Conic (<b>−JL</b>) and Albers Equal-Area
(<b>−JB</b>) will use the spherical solution when the
map scale exceeds 1.0E7. (2) Transverse Mercator
(<b>−JT</b>) and UTM (<b>−JU</b>) will will use
the spherical solution when either the west or east boundary
given in <b>−R</b> is more than 10 degrees from the
central meridian, and (3) same for Cassini
(<b>−JC</b>) but with a limit of only 4 degrees.</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),
<i><A HREF="gmtdefaults.html">gmtdefaults</A></i>(1), <i><A HREF="mapproject.html">mapproject</A></i>(1)</p>
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