Mercator maps?

[John Biddiscombe]

>I have a need of making flat mercator maps of the earth and displaying a
surface 
>above it.  I know VTK has an EarthSource and I can display the surface
above it 
>(thanks Ken!), but its a round globe.  I'd like to do the same thing on a
flat 
>map of the earth.
>
>Any ideas how I could convert the data in the EarthSource to a flat plane 
>instead of a sphere?

Yes. we have a 

vtkOStoXYZ filter which converts UK ordnance survey coordinates (Airy 1936
Mercator projection) to Lat/Long or cartesian geocentric {x,y,z} coords (&
vice versa). Adding datum shifts and other ellipsoids etc etc is not a
problem.

Unfortunately I can't send you the code for commercial/copyright reasons,
but all you need to do is get hold of a Lat/Long to Mercator equation
depending on which regional mercator ellipsoid thingy you're using, then
make a vtkPointSettoPointSet filter or similar insert the conversion and
bung the data from the earthsource through it. It sounds harder than it is
but plotting 3D terrain overlaid on the globe looks ace. 

John B



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