```

```

## NAME

```       nearneighbor - A "Nearest neighbor" gridding algorithm

```

## SYNOPSIS

```       nearneighbor  [  xyzfile(s)  ]  -Gout_grdfile -Ix_inc[m|c][/y_inc[m|c]]
]  [  -F ] [ -H[nrec] ] [ -Lflag ] [ -V ] [ -W ] [ -: ] [ -bi[s][n] ] [
-f[i|o]colinfo ]

```

## DESCRIPTION

```       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 pointsâ€™ weights [if sup-
plied].

xyzfile(s)
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[:ss.xxx][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].

```

## OPTIONS

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

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

be changed by editing your  .gmtdefaults4  file.  If  used,  GMT
default  is  1  header record. Use -Hi if only input data should
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
file(s).
[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.

```

## 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:

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, run

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

```

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