man grdedit () - Modifying the header in a 2-D grdfile


grdedit - Modifying the header in a 2-D grdfile


grdedit grdfile [ -A ] [ -Dxunit/yunit/zunit/scale/offset/title/remark ] [ -Rwest/east/south/north[r] ] [ -S ] [ -V ]


grdedit reads the header information in a binary 2-D grdfile and replaces the information with values provided on the command line [if any]. As an option, global, geographical grids (with 360 degrees longitude range) can be rotated in the east-west direction. grdedit only operates on files containing a grdheader.

No space between the option flag and the associated arguments. Use upper case for the option flags and lower case for modifiers.

Name of the 2-D grdfile to modify


If necessary, adjust the file's x_inc, y_inc to be compatible with its domain (or a new domain set with -R). Older gridfiles (i.e., created prior to GMT 3.1) often had excessive slop in' x_inc, y_inc and an adjustment is necessary. Newer files are created correctly.
Give new values for xunit, yunit, zunit, scale, offset, title, and remark. To leave some of the values untouched, specify = as the new value.
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. The new w/e/s/n values will replace those in the grid, and the x_inc, y_inc values are adjusted, if necessary.
For global, geographical grids only. Grid values will be shifted laterally according to the new borders given in -R.
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].


Let us assume the file data.grd covers the area 300/310/10/30. We want to change the boundaries from geodetic longitudes to geographic and put a new title in the header. We accomplish this by

grdedit data.grd -R-60/-50/10/30 -D=/=/=/=/=/"Gravity Anomalies"/=

The grid world.grd has the limits 0/360/-72/72. To shift the data so that the limits would be -180/180/-72/72, use

grdedit world.grd -R-180/180/-72/72 -S

The file junk.grd was created prior to GMT 3.1 with incompatible -R and -I arguments. To reset the x- and y-increments we run

grdedit junk.grd -A