Is that possible to fill the space between the contour lines using hachure patterns? Or use them in grdimage?

### Description of the desired feature

In many geo-related fields, we need to plot spatial distributions of composite values or trends together with their significant levels.
Many papers have those kinds of maps by showing the levels with dots/hatchure patterns.
However, I don't know there is a way to reproduce those figures with hatched significant fields in GMT.
Is there any way to plot some patterns/dots/lines over the significant values?

One potential way may be creating a grd file by replacing insignificant values with NaNs. Then, I could use grdimage to plot it using cmap, which contains hachure patterns instead of normal colors. But for now, I don't know how to do so, because hacure patterns only works when 'fill' or '-G' function is available.

By the way, the GMT example 16 (https://docs.generic-mapping-tools.org/dev/gallery/ex16.html) showed a way to use hatched cpt and grdview, but it is not 'elegent' way because we need to edit the cpt file manually. I think it could be possible to include such function inside the codes of GMT/PyGMT.

### Are you willing to help implement and maintain this feature?

No