grdsample - Resample a grd file onto a new grid
grdsample in_grdfile -Gout_grdfile [ -F ] [ -Idx[m|c][/dy[m|c]] ] [
-Lflag ] [ -Nnx/ny ] [ -Q ] [ -Rwest/east/south/north[r] ] [ -T ] [ -V
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.
The name of the input 2-D binary grd file.
-G The name of the output grd file.
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
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
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.
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
grdsample surface.grd -T -Gpixel.grd
gmt, grdedit, grdfft, grdfilter
Man(1) output converted with