[ferret_users] shade: a cross section with the surface topography filled at thebottom?

[Emilie Vanvyve <vanvyve@xxxxxxxxxxxxxx>]

Dear Ferret users,

I looked at the online help, found some clues to help me, but I  
haven't succeeded so far and thought of submitting my question to you.

I plot a cross section of the zonal wind with a simple "shade/x=0/l=1/ 
vlimit=1000:0:-100 uairdy,lat,pressure". The resulting graph is  
joined to this email.
How can I get the imitation of the surface topography (the white  
area) shaded in grey or black or whatever colour?

In the sigma_coordinate_demo.jnl script, some similar graphs are made  
and obviously succeeded where I fail. But the problem is taken  
backwards: first the topography is defined (variable "bathymetry"),  
then the variable is computed, then the variable is plotted, then the  
bathymetry is overlayed.
How can I compute the surface topography from my data? I can get the  
value of the pressure at the surface, but I haven't succeeded to make  
it 3D "under the surface" and even less to plot it nicely.

Would anybody know how to do?

Many thanks in advance,

Emilie