NAME

       nearneighbor - "Grid table data using a ""Nearest neighbor"" algorithm"

SYNOPSIS

       nearneighbor [ table ] out_grdfile increment sectors[/min_sectors] region [ search_radius[unit] [ empty ]
       [  [level] ] [  ] [ -bi<binary> ] [ -di<nodata> ] [ -f<flags> ] [ -h<headers> ] [ -i<flags> ] [ -n<flags>
       ] [ -r ] [ -:[i|o] ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       nearneighbor reads arbitrarily located (x,y,z[,w]) triples [quadruplets] from standard input  [or  table]
       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].

REQUIRED ARGUMENTS

       -Gout_grdfile
              Give the name of the output grid file.

       -Ixinc[unit][=|+][/yinc[unit][=|+]]
              x_inc [and  optionally  y_inc]  is  the  grid  spacing.  Optionally,  append  a  suffix  modifier.
              Geographical (degrees) coordinates: Append m to indicate arc minutes or s to indicate arc seconds.
              If  one  of the units e, f, k, M, n or u 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 /y_inc is given but set to 0 it will be reset equal  to  x_inc;  otherwise  it
              will  be  converted  to degrees latitude. All coordinates: If = is appended then the corresponding
              max x (east) or y (north) 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 number of nodes desired by  appending  +  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 -Rgrdfile is used then the grid
              spacing has already been initialized; use -I to override the values.

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

       -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
              Specify the region of interest.

       -Ssearch_radius[unit]
              Sets  the  search_radius  that determines which data points are considered close to a node. Append
              the distance unit (see UNITS).

OPTIONAL ARGUMENTS

       table  3 [or 4, see -W] column ASCII file(s) [or binary, see -bi] holding (x,y,z[,w]) data values. If  no
              file is specified, nearneighbor will read from standard input.

       -Eempty
              Set the value assigned to empty nodes [NaN].

       -V[level] (more ...)
              Select verbosity level [c].

       -W     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.

       -bi[ncols][t] (more ...)
              Select native binary input. [Default is 3 (or 4 if -W is set) columns].

       -dinodata (more ...)
              Replace input columns that equal nodata with NaN.

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -icols[l][sscale][ooffset][,...] (more ...)
              Select input columns (0 is first column).

       -n[b|c|l|n][+a][+bBC][+tthreshold]
              Append +bBC to set any boundary conditions to be used, adding g for geographic, p for periodic, or
              n for natural boundary conditions. For the latter two you may append x or y to  specify  just  one
              direction, otherwise both are assumed.  [Default is geographic if grid is geographic].

       -r (more ...)
              Set pixel node registration [gridline].

       -:[i|o] (more ...)
              Swap 1st and 2nd column on input and/or output.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).

       -+ or just +
              Print  an  extensive usage (help) message, including the explanation of any module-specific option
              (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation of options, then exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

UNITS

       For map distance unit, append unit d for arc degree, m for arc minute, and s for arc  second,  or  e  for
       meter [Default], f for foot, k for km, M for statute mile, n for nautical mile, and u for US survey foot.
       By  default  we compute such distances using a spherical approximation with great circles. Prepend - to a
       distance (or the unit is no distance is given) to perform "Flat Earth"  calculations  (quicker  but  less
       accurate) or prepend + to perform exact geodesic calculations (slower but more accurate).

GRID VALUES PRECISION

       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.

EXAMPLES

       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:

              gmt nearneighbor seaMARCII_bathy.lon_lat_z -R242/244/-22/-20 -I0.5m \
                               -E-9999 -Gbathymetry.nc -S5k -N8/8

       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:

              gmt nearneighbor geoid.xyz -R0/360/-90/90 -I1 -Lg -Ggeoid.nc -S200k -N4

SEE ALSO

       blockmean, blockmedian, blockmode, gmt, greenspline, sphtriangulate, surface, triangulate

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.2.1                                           January 28, 2016                              NEARNEIGHBOR(1gmt)