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] ] [ -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
              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 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 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 spacing; 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 registration].

       -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  conditions].   If  no  flag  is  given, it is assumed that the x column contains
              longitudes, which may differ from the region in -R by [multiples of] 360 degrees [Default  assumes
              no periodicity].

       -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)].  Applies to geographic coordinates only.

       -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    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(1gmt), blockmedian(1gmt), blockmode(1gmt), gmt(1gmt), surface(1gmt), triangulate(1gmt)

                                                   1 Jan 2004                                    NEARNEIGHBOR(l)