NAME

       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 bicubic [Default] or bilinear (-Q) and uses boundary conditions (-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 arguments.

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

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

       -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
              uses "natural" conditions (second partial derivative normal to edge is zero).]

       -N     Specify number of columns nx and rows ny of new grid.

       -Q     Quick mode, use bilinear rather than bicubic interpolation.

       -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.

       -T     Translate  between grid and pixel registration while keeping -R and -I the same; if input is grid-
              registered, output will be pixel-registered and vice-versa. The input file determines -R,  -I  and
              -N so 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
       surrounding the point will yield an interpolated NaN. Bicubic interpolation [default]  yields  continuous
       first  derivatives  but  requires  a neighborhood of 4 nodes by 4 nodes. Bilinear interpolation [-Q] uses
       only a 2 by 2 neighborhood, 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(1gmt), grdedit(1gmt), grdfft(1gmt), grdfilter(1gmt)

                                                   1 Jan 2004                                       GRDSAMPLE(l)