grdsample

       grdsample - Resample a grd file onto a new grid

SYNOPSIS

       grdsample    in_grdfile    -Gout_grdfile    [   -F   ]   [
       -Idx[m|c][/dy[m|c]] ] [ -Lflag ] [ -Nnx/ny  ]  [  -Q  ]  [
       -Rwest/east/south/north[r] ] [ -T ] [ -V ]

DESCRIPTION

       grdsample  reads a grdfile and interpolates it to create a
       new grdfile with either: a  different  registration  (-T);
       or,  a  new grid-spacing (-I) or number of nodes (-N), and
       perhaps also a new sub-region (-R). Interpolation is bicu­
       bic  [Default]  or  bilinear (-Q) and uses boundary condi­
       tions (-L).  Note that using (-R) only  is  equivalent  to
       grdcut or grdedit -S. grdsample safely creates a fine mesh
       from a coarse one; the converse may suffer aliasing unless
       the data are filtered using grdfft or grdfilter.

       in_grdfile
              The name of the input 2-D binary grd file.

       -G     The name of the output grd file.

OPTIONS

       No  space between the option flag and the associated argu­
       ments.

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

       -I     x_inc  [and  optionally y_inc] is the grid spacing.
              Append m to indicate minutes or c to indicate  sec­
              onds.

       -L     Boundary  condition  flag may be x or y or xy indi­
              cating 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 uses
              "natural"  conditions  (second  partial  derivative
              normal to edge is zero).]

       -Q     Quick mode, use bilinear rather than bicubic inter­
              polation.

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

       -T     Translate between grid and pixel registration while
              keeping -R and -I the same; if input is grid-regis­
              no  other options are necessary (except possibly -L
              or -Q).

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

HINTS

       If  an  interpolation  point is not on a node of the input
       grid, then a NaN at any node in the neighborhood surround­
       ing  the  point  will  yield  an interpolated NaN. Bicubic
       interpolation [default] yields  continuous  first  deriva­
       tives  but  requires a neighborhood of 4 nodes by 4 nodes.
       Bilinear interpolation [-Q] uses only a 2 by  2  neighbor­
       hood, but yields only zeroth-order continuity. Use bicubic
       when smoothness is important. Use bilinear to minimize the
       propagation of NaNs.

EXAMPLES

       To  resample the 5 x 5 minute grid in hawaii_5by5_topo.grd
       onto a 1 minute grid, try

       grdsample hawaii_5by5_topo.grd -I1m -Ghawaii_1by1_topo.grd

       To  translate  the gridline-registered file surface.grd to
       pixel registration, try

       grdsample surface.grd -T -Gpixel.grd

SEE ALSO

       gmt(l), grdedit(l), grdfft(l), grdfilter(l)