Very likely, this has a simple answer… how do I inform GMT that a 1-degree square region is “geographic?” I need to create a zero-level grid (i.e., all z = 0).
gmt grdmath -R3/4/51/52 -I1s/1s 0 = t.grd
yields this response:
grdmath [WARNING]: Unit s is ignored as the x-axis is not geographic grdmath [WARNING]: Unit s is ignored as the y-axis is not geographic
And, when checking that the grid was made with a one arcsec increment, this results:
> gmt grdinfo t.grd t.grd: Title: Produced by grdmath t.grd: Command: grdmath -R3/4/51/52 -I1s/1s 0 = t.grd t.grd: Remark: t.grd: Gridline node registration used [Cartesian grid] t.grd: Grid file format: nf = GMT netCDF format (32-bit float), CF-1.7 t.grd: x_min: 3 x_max: 4 x_inc: 1 name: x n_columns: 2 t.grd: y_min: 51 y_max: 52 y_inc: 1 name: y n_rows: 2 t.grd: v_min: 0 v_max: 0 name: z t.grd: scale_factor: 1 add_offset: 0 t.grd: format: classic
I’ve tried several variants (-fg, and +d on the -R spec), and nothing seems to get past this. Must be something I missed.