grdreformat (1gmt)

grdreformat ingrdfile[=id[/scale/offset[/NaNvalue]]] outgrdfile[=id[/scale/offset[/NaNvalue]]] [ -Rwest/east/south/north[r] ] [ -V ]

grdreformat reads a grdfile in one format and writes it out using another format. As an option the user may select a subset of the data to be written and to specify scaling, translation, and NaN-value.

ingrdfile

The grdfile to be read. Append format =id number if not a standard GMT netcdf-based grdfile. If id is set, you may optionally append scale and offset to scale the data and then add an offset. If scale and offset are supplied you may also append a value that represent 'not-a-number' (for floating-point grids this is unneccesary since the IEEE NaN is used; however short integers need a value which means no data available.)

outgrdfile

The grdfile to be written. Append format =id number if not a standard GMT netcdf-based grdfile. If id is set, you may optionally append scale and offset to scale the data and then add an offset. If scale and offset are supplied you may also append a value that represent 'not-a-number' (for floating-point grids this is unneccesary since the IEEE NaN is used; however short integers need a value which means no data available.) For format =id > 0 the size of the GMT grdheader block is hsize = 896 bytes, and the total size of the file is hsize + nx * ny * item_size, where item_size is the size in bytes of each element (1, 2, 4). Bit grids are stored using 4-byte integers, each holding 32 bits, so for these files the size equation is modified by using ceil (nx / 32) * 4 instead of nx. For header and grid details, see Appendix B.

-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.

-V

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

To create a 4-byte raw floating point grid from the netcdf file data.grd, try

grdreformat data.grd ras_data.b4=1 -V

To make a 2-byte short integer file, scale it by 10, subtract 32000, setting NaNs to -9999, do

grdreformat values.grd shorts.i2=2/10/-32000/-9999 -V

To create a Sun standard 8-bit rasterfile for a subset of the data file image.grd, assuming the range in image.grd is 0-1 and we need 0-255, try

grdreformat image.grd -R-60/-40/-40/-30 image.ras8=3/255/0 -V

gmt(1gmt), grdmath(1gmt)