.\" Man page generated from reStructuredText.
.
.TH "NEARNEIGHBOR" "1gmt" "May 21, 2019" "5.4.5" "GMT"
.SH NAME
nearneighbor \- "Grid table data using a ""Nearest neighbor"" algorithm"
.
.nr rst2man-indent-level 0
.
.de1 rstReportMargin
\\$1 \\n[an-margin]
level \\n[rst2man-indent-level]
level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
-
\\n[rst2man-indent0]
\\n[rst2man-indent1]
\\n[rst2man-indent2]
..
.de1 INDENT
.\" .rstReportMargin pre:
. RS \\$1
. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
. nr rst2man-indent-level +1
.\" .rstReportMargin post:
..
.de UNINDENT
. RE
.\" indent \\n[an-margin]
.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
.nr rst2man-indent-level -1
.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
..
.SH SYNOPSIS
.sp
\fBnearneighbor\fP [ \fItable\fP ]  \fB\-G\fP\fIout_grdfile\fP
 \fB\-I\fP\fIincrement\fP
 \fB\-N\fP\fIsectors\fP[/\fImin_sectors\fP]
 \fB\-R\fP\fIregion\fP
 \fB\-S\fP\fIsearch_radius\fP[\fIunit\fP]
[  \fB\-E\fP\fIempty\fP ]
[  \fB\-V\fP[\fIlevel\fP] ]
[  \fB\-W\fP ]
[ \fB\-bi\fPbinary ]
[ \fB\-di\fPnodata ]
[ \fB\-e\fPregexp ]
[ \fB\-f\fPflags ]
[ \fB\-h\fPheaders ]
[ \fB\-i\fPflags ]
[ \fB\-n\fPflags ]
[ \fB\-r\fP ]
[ \fB\-:\fP[\fBi\fP|\fBo\fP] ]
.sp
\fBNote:\fP No space is allowed between the option flag and the associated arguments.
.SH DESCRIPTION
.sp
\fBnearneighbor\fP reads arbitrarily located (x,y,z[,w]) triples
[quadruplets] from standard input [or \fItable\fP] 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 weights of the observation points [if
supplied].
.SH REQUIRED ARGUMENTS
.INDENT 0.0
.TP
\fB\-G\fP\fIout_grdfile\fP
Give the name of the output grid file.
.UNINDENT
.INDENT 0.0
.TP
\fB\-I\fP\fIxinc\fP[\fIunit\fP][\fB+e\fP|\fBn\fP][/\fIyinc\fP[\fIunit\fP][\fB+e\fP|\fBn\fP]]
\fIx_inc\fP [and optionally \fIy_inc\fP] is the grid spacing. Optionally,
append a suffix modifier. \fBGeographical (degrees) coordinates\fP: Append
\fBm\fP to indicate arc minutes or \fBs\fP to indicate arc seconds. If one
of the units \fBe\fP, \fBf\fP, \fBk\fP, \fBM\fP, \fBn\fP or \fBu\fP is appended
instead, the increment is assumed to be given in meter, foot, km, Mile,
nautical mile or US survey foot, respectively, and will be converted to
the equivalent degrees longitude at the middle latitude of the region
(the conversion depends on PROJ_ELLIPSOID). If \fIy_inc\fP is given
but set to 0 it will be reset equal to \fIx_inc\fP; otherwise it will be
converted to degrees latitude. \fBAll coordinates\fP: If \fB+e\fP is appended
then the corresponding max \fIx\fP (\fIeast\fP) or \fIy\fP (\fInorth\fP) 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 \fInumber of nodes\fP desired by
appending \fB+n\fP 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 App\-file\-formats for
details. Note: if \fB\-R\fP\fIgrdfile\fP is used then the grid spacing has
already been initialized; use \fB\-I\fP to override the values.
.UNINDENT
.INDENT 0.0
.TP
\fB\-N\fP\fIsectors\fP[/\fImin_sectors\fP]
The circular area centered on each node is divided into \fIsectors\fP
sectors. Average values will only be computed if there is at least
one value inside each of at least \fImin_sectors\fP of the sectors for a given
node. Nodes that fail this test are assigned the value NaN (but see
\fB\-E\fP). If \fImin_sectors\fP is omitted it is set to be at least 50%
of \fIsectors\fP (i.e., rounded up to next integer).  [Default is a quadrant
search with 100% coverage, i.e., \fIsectors\fP = \fImin_sectors\fP = 4]. Note
that only the nearest value per sector enters into the averaging; the
more distant points are ignored.
.UNINDENT
.INDENT 0.0
.TP
\fB\-R\fP\fIxmin\fP/\fIxmax\fP/\fIymin\fP/\fIymax\fP[\fB+r\fP][\fB+u\fP\fIunit\fP] (more ...)
Specify the region of interest.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-S\fP\fIsearch_radius\fP[\fIunit\fP]
Sets the \fIsearch_radius\fP that determines which data points are
considered close to a node. Append the distance unit (see UNITS).
.UNINDENT
.SH OPTIONAL ARGUMENTS
.INDENT 0.0
.TP
.B \fItable\fP
3 [or 4, see \fB\-W\fP] column ASCII file(s) [or binary, see
\fB\-bi\fP] holding (x,y,z[,w]) data values. If
no file is specified, \fBnearneighbor\fP will read from standard input.
.UNINDENT
.INDENT 0.0
.TP
\fB\-E\fP\fIempty\fP
Set the value assigned to empty nodes [NaN].
.UNINDENT
.INDENT 0.0
.TP
\fB\-V\fP[\fIlevel\fP] (more ...)
Select verbosity level [c].  
.UNINDENT
.INDENT 0.0
.TP
\fB\-W\fP
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.
.UNINDENT
.INDENT 0.0
.TP
\fB\-bi\fP[\fIncols\fP][\fBt\fP] (more ...)
Select native binary input. [Default is 3 (or 4 if \fB\-W\fP is set) columns].
.UNINDENT
.INDENT 0.0
.TP
\fB\-di\fP\fInodata\fP (more ...)
Replace input columns that equal \fInodata\fP with NaN.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-e\fP[\fB~\fP]\fI"pattern"\fP \fB|\fP \fB\-e\fP[\fB~\fP]/\fIregexp\fP/[\fBi\fP] (more ...)
Only accept data records that match the given pattern.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-f\fP[\fBi\fP|\fBo\fP]\fIcolinfo\fP (more ...)
Specify data types of input and/or output columns.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-h\fP[\fBi\fP|\fBo\fP][\fIn\fP][\fB+c\fP][\fB+d\fP][\fB+r\fP\fIremark\fP][\fB+r\fP\fItitle\fP] (more ...)
Skip or produce header record(s).  
.UNINDENT
.INDENT 0.0
.TP
\fB\-i\fP\fIcols\fP[\fB+l\fP][\fB+s\fP\fIscale\fP][\fB+o\fP\fIoffset\fP][,\fI\&...\fP] (more ...)
Select input columns and transformations (0 is first column).
.TP
\fB\-n\fP[\fBb\fP|\fBc\fP|\fBl\fP|\fBn\fP][\fB+a\fP][\fB+b\fP\fIBC\fP][\fB+t\fP\fIthreshold\fP]
Append \fB+b\fP\fIBC\fP to set any boundary conditions to be used,
adding \fBg\fP for geographic, \fBp\fP for periodic, or \fBn\fP for
natural boundary conditions. For the latter two you may append \fBx\fP
or \fBy\fP to specify just one direction, otherwise both are assumed.
[Default is geographic if grid is geographic].
.UNINDENT
.INDENT 0.0
.TP
\fB\-r\fP (more ...)
Set pixel node registration [gridline].  
.UNINDENT
.INDENT 0.0
.TP
\fB\-:\fP[\fBi\fP|\fBo\fP] (more ...)
Swap 1st and 2nd column on input and/or output.
.UNINDENT
.INDENT 0.0
.TP
\fB\-^\fP or just \fB\-\fP
Print a short message about the syntax of the command, then exits (NOTE: on Windows just use \fB\-\fP).
.TP
\fB\-+\fP or just \fB+\fP
Print an extensive usage (help) message, including the explanation of
any module\-specific option (but not the GMT common options), then exits.
.TP
\fB\-?\fP or no arguments
Print a complete usage (help) message, including the explanation of all options, then exits.
.UNINDENT
.SH UNITS
.sp
For map distance unit, append \fIunit\fP \fBd\fP for arc degree, \fBm\fP for arc
minute, and \fBs\fP for arc second, or \fBe\fP for meter [Default], \fBf\fP
for foot, \fBk\fP for km, \fBM\fP for statute mile, \fBn\fP for nautical mile,
and \fBu\fP for US survey foot. By default we compute such distances using
a spherical approximation with great circles. Prepend \fB\-\fP to a
distance (or the unit is no distance is given) to perform "Flat Earth"
calculations (quicker but less accurate) or prepend \fB+\fP to perform
exact geodesic calculations (slower but more accurate).
.SH GRID VALUES PRECISION
.sp
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.
.SH EXAMPLES
.sp
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:
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt nearneighbor seaMARCII_bathy.lon_lat_z \-R242/244/\-22/\-20 \-I0.5m \e
                 \-E\-9999 \-Gbathymetry.nc \-S5k \-N8/8
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.sp
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:
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt nearneighbor geoid.xyz \-R0/360/\-90/90 \-I1 \-Lg \-Ggeoid.nc \-S200k \-N4
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.SH SEE ALSO
.sp
blockmean,
blockmedian,
blockmode, gmt,
greenspline,
sphtriangulate,
surface,
triangulate
.SH COPYRIGHT
2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
.\" Generated by docutils manpage writer.
.