## 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).]

          -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, grdedit, grdfft, grdfilter