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)