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<!-- Creator     : groff version 1.22.2 -->
<!-- CreationDate: Thu Feb 27 18:13:09 2014 -->
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<title>NEARNEIGHBOR</title>

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<body bgcolor="#ffffff">

<h1 align="center">NEARNEIGHBOR</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 VALUES PRECISION">GRID VALUES PRECISION</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">nearneighbor
&minus; A &quot;Nearest neighbor&quot; gridding
algorithm</p>

<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>



<p style="margin-left:11%; margin-top: 1em"><b>nearneighbor</b>
[ <i>xyzfile(s)</i> ] <b>&minus;G</b><i>out_grdfile</i>
<b>&minus;I</b><i>xinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>][/<i>yinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>]]
<b>&minus;N</b><i>sectors</i>[/<i>min_sectors</i>]
<b>&minus;R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
<b>&minus;S</b><i>search_radius</i>[<b>m</b>|<b>c</b>|<b>k</b>|<b>K</b>]
[ <b>&minus;E</b><i>empty</i> ] [ <b>&minus;F</b> ] [
<b>&minus;H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>&minus;L</b><i>flag</i> ] [ <b>&minus;V</b> ] [
<b>&minus;W</b> ] [ <b>&minus;:</b>[<b>i</b>|<b>o</b>] ] [
<b>&minus;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>&minus;f</b><i>colinfo</i> ]</p>

<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>



<p style="margin-left:11%; margin-top: 1em"><b>nearneighbor</b>
reads arbitrarily located (x,y,z[,w]) triples [quadruplets]
from standard input [or <i>xyzfile(s)</i>] and uses a
nearest neighbor algorithm to assign an average value to
each node that have one or more points within a radius
centered on the node. The average value is computed as a
weighted mean of the nearest point from each sector inside
the search radius. The weighting function used is w(r) = 1 /
(1 + d ^ 2), where d = 3 * r / search_radius and r is
distance from the node. This weight is modulated by the
observation points&rsquo; weights [if supplied]. <i><br>
xyzfile(s)</i></p>

<p style="margin-left:22%;">3 [or 4, see <b>&minus;W</b>]
column ASCII file(s) [or binary, see <b>&minus;b</b>]
holding (x,y,z[,w]) data values. If no file is specified,
<b>nearneighbor</b> will read from 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><b>&minus;G</b></p></td>
<td width="8%"></td>
<td width="78%">


<p>Give the name of the output grid file.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">


<p><b>&minus;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>&minus;R</b><i>grdfile</i> is used then grid spacing has
already been initialized; use <b>&minus;I</b> to override
the values.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">


<p><b>&minus;N</b></p></td>
<td width="8%"></td>
<td width="78%">


<p>The circular area centered on each node is divided into
<i>sectors</i> sectors. Average values will only be computed
if there is at least one value inside each of at least
<i>min_sectors</i> of these sectors for a given node. Nodes
that fail this test are assigned the value NaN (but see
<b>&minus;E</b>). If <i>min_sectors</i> is omitted it is set
to be at least 50% of <i>sectors</i> (i.e., rounded up to
next integer). [Default is a quadrant search with 100%
coverage, i.e., <i>sectors</i> = <i>min_sectors</i> = 4].
Note that only the nearest value per sector enters into the
averaging; the more distant points are ignored.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">


<p><b>&minus;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>&minus;Rg</b> and
<b>&minus;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>&minus;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>&minus;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>&minus;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>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">


<p><b>&minus;S</b></p></td>
<td width="8%"></td>
<td width="78%">


<p>Sets the <i>search_radius</i> in same units as the grid
spacing; append <b>m</b> to indicate minutes or <b>c</b> to
indicate seconds. Append <b>k</b> to indicate km (implies
<b>&minus;R</b> and <b>&minus;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.</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>&minus;E</b></p></td>
<td width="7%"></td>
<td width="78%">


<p style="margin-top: 1em">Set the value assigned to empty
nodes [NaN].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;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>&minus;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>&minus;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. Not used with binary data.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;L</b></p></td>
<td width="7%"></td>
<td width="78%">


<p>Boundary condition <i>flag</i> may be <i>x</i> or
<i>y</i> or <i>xy</i> indicating data is periodic in range
of x or y or both set by <b>&minus;R</b>, or <i>flag</i> may
be <i>g</i> indicating geographical conditions (x and y are
lon and lat). [Default is no boundary conditions].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;V</b></p></td>
<td width="7%"></td>
<td width="78%">


<p>Selects verbose mode, which will send progress reports
to stderr [Default runs &quot;silently&quot;].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;:</b></p></td>
<td width="7%"></td>
<td width="78%">


<p>Toggles between (longitude,latitude) and
(latitude,longitude) input and/or output. [Default is
(longitude,latitude)]. Append <b>i</b> to select input only
or <b>o</b> to select output only. [Default affects
both].</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;W</b></p></td>
<td width="7%"></td>
<td width="78%">


<p>Input data have a 4th column containing observation
point weights. These are multiplied with the geometrical
weight factor to determine the actual weights used in the
calculations.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;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 3 (or 4 if
<b>&minus;W</b> is set) columns].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">


<p><b>&minus;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>&minus;f</b>[<b>i</b>|<b>o</b>]<b>g</b> means
<b>&minus;f</b>[<b>i</b>|<b>o</b>]0<b>x</b>,1<b>y</b>
(geographic coordinates).</p></td></tr>
</table>

<h2>GRID VALUES PRECISION
<a name="GRID VALUES PRECISION"></a>
</h2>


<p style="margin-left:11%; margin-top: 1em">Regardless of
the precision of the input data, GMT programs that create
grid files will internally hold the grids in 4-byte floating
point arrays. This is done to conserve memory and
furthermore most if not all real data can be stored using
4-byte floating point values. Data with higher precision
(i.e., double precision values) will lose that precision
once GMT operates on the grid or writes out new grids. To
limit loss of precision when processing data you should
always consider normalizing the data prior to
processing.</p>

<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>


<p style="margin-left:11%; margin-top: 1em">To create a
gridded data set from the file seaMARCII_bathy.lon_lat_z
using a 0.5 min grid, a 5 km search radius, using an octant
search with 100% sector coverage, and set empty nodes to
-9999:</p>


<p style="margin-left:11%; margin-top: 1em"><b>nearneighbor</b>
seaMARCII_bathy.lon_lat_z <b>&minus;R</b> 242/244/-22/-20
<b>&minus;I</b> 0.5<b>m &minus;E</b>-9999 <b>&minus;G</b>
bathymetry.grd <b>&minus;S</b> 5<b>k &minus;N</b> 8/8</p>

<p style="margin-left:11%; margin-top: 1em">To make a
global grid file from the data in geoid.xyz using a 1 degree
grid, a 200 km search radius, spherical distances, using an
quadrant search, and set nodes to NaN only when fewer than
two quadrants contain at least one value:</p>


<p style="margin-left:11%; margin-top: 1em"><b>nearneighbor</b>
geoid.xyz <b>&minus;R</b> 0/360/-90/90 <b>&minus;I</b> 1
<b>&minus;L</b> g <b>&minus;G</b> geoid.grd <b>&minus;S</b>
200K <b>&minus;N</b> 4</p>

<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>



<p style="margin-left:11%; margin-top: 1em"><i><A HREF="blockmean.html">blockmean</A></i>(1),
<i><A HREF="blockmedian.html">blockmedian</A></i>(1), <i><A HREF="blockmode.html">blockmode</A></i>(1), <i><A HREF="GMT.html">GMT</A></i>(1),
<i><A HREF="surface.html">surface</A></i>(1), <i><A HREF="triangulate.html">triangulate</A></i>(1)</p>
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