Provided by: gmt-common_5.4.3+dfsg-1_all bug


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


       nearneighbor [ table ]  -Gout_grdfile
        -Ssearch_radius[unit]  [   -Eempty ] [  -V[level] ] [  -W ] [ -bibinary ] [ -dinodata ] [
       -eregexp ] [ -fflags ] [ -hheaders ] [ -iflags ] [ -nflags ] [ -r ] [ -:[i|o] ]

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


       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].


              Give the name of the output grid file.

              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 +e 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  +n 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.

              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.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
              Specify the region of interest.

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


       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.

              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.

       -e[~]”pattern” | -e[~]/regexp/[i] (more …)
              Only accept data records that match the given pattern.

       -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 and transformations (0 is first column).

              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
              just use -).

       -+ 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 all options,
              then exits.


       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).


       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


       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 -S5k -N8/8

       To  make  a  global  grid  file from the data in 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 -R0/360/-90/90 -I1 -Lg -S200k -N4


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


       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe