grdsample(1) 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.
The name of the output grd file.


No space between the option flag and the associated arguments.
Force pixel registration. [Default is grid registration].
x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds.
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).]
Specify number of columns nx and rows ny of new grid.
Quick mode, use bilinear rather than bicubic interpolation.
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.
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).
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 registration, try

grdsample surface.grd -T -Gpixel.grd