Vertical sections for irregular data/regridding

[Hartmut Frenzel <frenzel@xxxxxxxxxxxxxxxxxxxxx>]

Hello,

I have a question regarding regridding of variables in order to create
vertical cross-sections.

My data are on an irregular sigma-coordinate grid, i.e. I have these
variables:

dimensions:
	xi_rho = 64 ;
	eta_rho = 128 ;
	s_rho = 20 ;
	time = UNLIMITED ; // (73 currently)
variables:
	float lon_rho(eta_rho, xi_rho) ;
		lon_rho:long_name = "longitude of RHO-points" ;
		lon_rho:units = "degree_east" ;
	float lat_rho(eta_rho, xi_rho) ;
		lat_rho:long_name = "latitude of RHO-points" ;
		lat_rho:units = "degree_north" ;
	float temp(time, s_rho, eta_rho, xi_rho) ;
		temp:long_name = "potential temperature" ;
		temp:units = "Celsius" ;

I also have actual depths (computed with Matlab):
	float depth(time, s_rho, eta_rho, xi_rho) ;

I understand how to plot vertical cross-sections along the indexed axes,
e.g.

define axis/z=0:4000:10/unit=meters/depth zdepth
let temp_on_depth = zaxreplace(temp,depth, z[gz=zdepth])
shade temp_on_depth[j=40,l=@ave]


However, I would like to create vertical cross-sections along specified
lines
in real-world coordinates, as described in the sample code in

http://ferret.wrc.noaa.gov/Ferret/Mail_Archives/fu_2002/msg00140.html

But that example used the levitus_climatology input file, which has
a regular (lon,lat) grid. I know that I have to do some regridding, but
I can't
figure out the exact syntax.

Any help is greatly appreciated.

-- Hartmut
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