NAME

     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] ] [ -Lflag ] [ -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 cen-
     tered 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 seconds.

     -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  sec-
          tors  for  a given node.  Nodes that fail this test are
          assigned the value NaN (but see -E).  [Default is  qua-
          drant  search,  i.e., sectors = 4].  Note that only the
          nearest value per sector enters into the averaging, not
          all values inside the circle.

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

     -S   Sets the search_radius in same units as the grid  spac-
          ing;  append  m  to  indicate  minutes or c to indicate
          seconds.  Append k to indicated km (implies -R  -I  are
          in  degrees);  use  uppercase  K if distances should be
          calculated using great circles [k uses flat Earth].


OPTIONS

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

     -F   Force pixel registration.  [Default is  grid  registra-
          tion].

     -H   Input file(s) has Header record(s).  Number  of  header
          records  can  be  changed  by editing your .gmtdefaults
          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  indicating
          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 condi-
          tions]

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

     -:   Toggles      between      (longitude,latitude)      and
          (latitude,longitude)    input/output.     [Default   is
          (longitude,latitude)].

     -W   Input data have a  4th  column  containing  observation
          point weights.  These are multiplied with the geometri-
          cal 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
     seaMARCII_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
     distances, using an quadrant search, and set empty nodes  to
     NaN, try

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



SEE ALSO

     blockmean(l),    blockmedian(l),    blockmode(l),    gmt(l),
     surface(l), triangulate(l)