nearneighbor

       nearneighbor - A "Nearest neighbor" gridding algorithm

SYNOPSIS

       nearneighbor      [     xyzfile(s)     ]     -Gout_grdfile
       -Ix_inc[m|c][/y_inc[m|c]]                        -Nsectors
       -Rwest/east/south/north[r]    -Ssearch_radius[m|c|k|K]   [
       -Eempty ] [ -F ] [ -H[nrec] ] [ -L[flag] ] [ -V ] [ -W ] [
       -: ] [ -bi[s][n] ]

DESCRIPTION

       nearneighbor reads arbitrarily located (x,y,z[,w]) triples
       [quadruplets] from standard input [or xyzfile(s)] 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) =
       1.0 / (1 + d ^ 2), where d = 3 * r / search_radius  and  r
       is distance from the node. This weight is modulated by the
       observation points' weights [if supplied].'

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

       -G     Give the name of the output grdfile.

       -I     x_inc  [and  optionally y_inc] is the grid spacing.
              Append m to indicate minutes or c to indicate  sec­
              onds.

       -N     The  circular area centered on each node is divided
              into several sectors. Average values will  only  be
              computed if there is at least one value inside each
              of the sectors for a given node.  Nodes  that  fail
              this  test are assigned the value NaN (but see -E).
              [Default is quadrant search, i.e.,  sectors  =  4].
              Note  that only the nearest value per sector enters
              into the averaging, not all values inside the  cir­
              cle.

       -R     west,  east, south, and north specify the Region of
              interest. To specify boundaries in degrees and min­
              utes  [and  seconds],  use  the  dd:mm[:ss] format.
              Append r if lower left and upper right map  coordi­
              nates are given instead of wesn.

       -S     Sets  the  search_radius  in same units as the grid
              spacing; append m to indicate minutes or c to indi­
              cate  seconds. Append k to indicated km (implies -R
              flat Earth].

OPTIONS

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

       -F     Force pixel registration. [Default is  grid  regis­
              tration].

       -H     Input  file(s)  has  Header  record(s).  Number  of
              header records can be changed by editing your .gmt­
              defaults  file.  If  used,  GMT default is 1 header
              record.  Not used with binary data.

       -L     Boundary condition flag may be x or y or  xy  indi­
              cating  data is periodic in range of x or y or both
              set by -R, or flag may be g indicating geographical
              conditions  (x  and y are lon and lat). [Default is
              no boundary conditions].  If no flag is  given,  it
              is  assumed  that the x column contains longitudes,
              which may differ from the region in -R  by  [multi­
              ples  of] 360 degrees [Default assumes no periodic­
              ity].

       -V     Selects verbose  mode,  which  will  send  progress
              reports to stderr [Default runs "silently"].

       -:     Toggles  between  (longitude,latitude)  and  (lati­
              tude,longitude) input/output. [Default  is  (longi­
              tude,latitude)].  Applies to geographic coordinates
              only.

       -W     Input data have a 4th column containing observation
              point  weights.  These are multiplied with the geo­
              metrical weight  factor  to  determine  the  actual
              weights used in the calculations.

       -bi    Selects binary input. Append s for single precision
              [Default is double].  Append n for  the  number  of
              columns in the binary file(s).  [Default is 3 (or 4
              if -W is set) columns].

EXAMPLES

       To  create  a  gridded  data  set  from  the   file   sea­
       MARCII_bathy.lon_lat_z using a 0.5 min grid, a 5 km search
       radius, using an octant search, and  set  empty  nodes  to
       -9999, try

       nearneighbor  seaMARCII_bathy.lon_lat_z  -R242/244/-22/-20
       -I.5m -E-9999 -Gbathymetry.grd -S5k -N8

       To make a global gridded file from the data  in  geoid.xyz
       using  a  1 degree grid, a 200 km search radius, spherical

       nearneighbor  geoid.xyz -R0/360/-90/90 -I1 -Lg -Ggeoid.grd
       -S20K -N4

SEE ALSO

       blockmean(l), blockmedian(l), blockmode(l),  gmt(l),  sur­
       face(l), triangulate(l)