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<h1 align=center>GRDBLEND</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="#RESTRICTIONS">RESTRICTIONS</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">grdblend
− Blend several partially over-lapping grids into one
large grid</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdblend</b>
<i>blendfile</i> <b>−G</b><i>grdfile</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>−N</b><i>nodata</i> ] [ <b>−Q</b> ] [
<b>−Z</b><i>scale</i> ] [ <b>−V</b> ] [
<b>−W</b> ] [ <b>−f</b><i>colinfo</i> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdblend</b>
reads a listing of grid files and blend parameters and
creates a binary grid file by blending the other grids using
cosine-taper weights. <b>grdblend</b> will report if some of
the nodes are not filled in with data. Such unconstrained
nodes are set to a value specified by the user [Default is
NaN]. Nodes with more than one value will be set to the
weighted average value. Note: Due to the row-by-row i/o
nature of operations in grdblend we only support the netCDF
and native binary grid formats for both input and output.
<i><br>
blendfile</i></p>
<p style="margin-left:22%;">ASCII file with one record per
grid file to include in the blend. Each record must contain
three items, separated by spaces or tabs: the gridfile name,
the <b>−R</b>-setting for the interior region, and the
relative weight <i>wr</i>. In the combined weighting scheme,
this grid will be given zero weight outside its domain,
weight = <i>wr</i> inside the interior region, and a 2-D
cosine-tapered weight between those end-members in the
boundary strip. However, if a negative <i>wr</i> is given
then the sense of tapering is inverted (i.e., zero weight
inside its domain). If the inner region should instead
exactly match the grid region then specify a - instead of
the <b>−R</b>-setting. If the ASCII file is not given
<b>grdblend</b> will read standard input.</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 binary output grid file. (See GRID FILE
FORMATS below). Only netCDF and native binary grid formats
are supported.</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>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>
</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>−N</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">No data. Set nodes
with no input grid to this value [Default is NaN].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Create a
header-less grid file suitable for use with
<b><A HREF="grdraster.html">grdraster</A></b>. Requires that the output grid file is a
native format (i.e., not netCDF).</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"].</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">Do not blend, just
output the weights used for each node. This option is valid
when only one input grid is provided [Default makes the
blend].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−Z</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Scale output values
by <i>scale</i> before writing to file. [1].</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="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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>
</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="GEOGRAPHICAL AND TIME COORDINATES"></a>
<h2>GEOGRAPHICAL AND TIME COORDINATES</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>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To create a
grid file from the four grid files piece_?.nc, make the
blendfile like this</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 valign="top">piece_1.nc</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="69%">
<p valign="top">-R<subregion_1> 1</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">piece_2.nc</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="69%">
<p valign="top">-R<subregion_2> 1</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">piece_3.nc</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="69%">
<p valign="top">-R<subregion_3> 1</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">piece_4.nc</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="69%">
<p valign="top">-R<subregion_4> 1</p></td>
</table>
<p style="margin-left:11%; margin-top: 1em">Then run</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdblend</b>
blend.job <b>−G</b> blend.nc
<b>−R</b><full_region>
<b>−I</b><dx/dy> <b>-V</b></p>
<a name="RESTRICTIONS"></a>
<h2>RESTRICTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">Currently, all
grids processed must have the exact same node registration
and grid spacing as the final output 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="grd2xyz.html">grd2xyz</A></i>(1), <i><A HREF="grdedit.html">grdedit</A></i>(1) <i><A HREF="grdraster.html">grdraster</A></i>(1)</p>
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