img2mercgrd(1gmt) on Linux
The text c06bbd9605b2, as Debian 5.0 (Lenny) shipped it.
Extract region of img, preserving Mercator, save as grd
Flags it lists
-
-C -
-D -
-G -
-N -
-R -
-S -
-T -
-V -
-W -
-m