nearneighbor - A "Nearest neighbor" gridding algorithm


       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] ] [
       -f[i|o]colinfo ]


       nearneighbor reads arbitrarily  located  (x,y,z[,w])  triples  [quadru-
       plets]  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 com-
       puted 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 sup-

              3 [or 4, see -W] column ASCII file(s) [or binary, see -b]  hold-
              ing (x,y,z[,w]) data values. If no file is specified, nearneigh-
              bor 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     xmin,  xmax,  ymin, and ymax specify the Region of interest. For
              geographic regions,  these  limits  correspond  to  west,  east,
              south,  and north and you may specify them in decimal degrees or
              in [+-]dd:mm[][W|E|S|N] format. Append r  if  lower  left
              and  upper  right map coordinates are given instead of wesn. The
              two shorthands  -Rg  -Rd  stand  for  global  domain  (0/360  or
              -180/+180  in longitude respectively, with -90/+90 in latitude).
              For calendar time coordinates you may either give relative  time
              (relative  to  the  selected  TIME_EPOCH  and  in  the  selected
              TIME_UNIT; append t to -JX|x), or  absolute  time  of  the  form
              [date]T[clock]  (append  T  to  -JX|x). At least one of date and
              clock must be present; the T is always required. The date string
              must  be  of  the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
              yyyy[-Www[-d]] (ISO week calendar), while the clock string  must
              be  of  the form hh:mm:ss[.xxx]. The use of delimiters and their
              type and positions must be as indicated  (however,  input/output
              and plotting formats are flexible).

       -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 and -I are in degrees); use uppercase K
              if distances should be calculated using great  circles  [k  uses
              flat Earth].


       -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  .gmtdefaults4  file.  If  used,  GMT
              default  is  1  header record. Use -Hi if only input data should
              have header records [Default will write out  header  records  if
              the input data have them].  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].

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

       -:     Toggles  between  (longitude,latitude)  and (latitude,longitude)
              input and/or output. [Default is (longitude,latitude)].   Append
              i  to  select  input  only  or o to select output only. [Default
              affects both].

       -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
              [Default is 3 (or 4 if -W is set) columns].

       -f     Special formatting of input and output  columns  (time  or  geo-
              graphical  data)  Specify  i(nput)  or o(utput) [Default is both
              input and output].  Give one or more columns (or column  ranges)
              separated by commas.  Append T (Absolute calendar time), t (time
              relative to chosen TIME_EPOCH), x (longitude), y  (latitude),  g
              (geographic coordinate), or f (floating point) to each column or
              column range item.


       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:

       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 using a 1
       degree grid, a 200 km search  radius,  spherical  distances,  using  an
       quadrant search, and set empty nodes to NaN, run

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


       blockmean(l),  blockmedian(l), blockmode(l), gmt(l), surface(l), trian-

GMT4.0                            1 Oct 2004                   NEARNEIGHBOR(l)

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