[Mapserver-users] Globe View with Orthographic Projection

[Harald Wehr]

I want to provide an earth view that looks like a globe. I therefore use 
the orthographic projection but get some problems here.

As I dont' know whether it is possible to attach binary files in this 
mailing list i put all example files under this url:

http://www2.hs-harz.de/~hwehr/mapserver/

I made 3 examples, every example has a map file, a template output and 
the resulting image.

Let me explain the examples. My data resides in a tif-file with world 
information in lat/lon format. Example 1 is working as you can see in 
the files containing the number 1. This example uses normal lat/lon 
projection.

In the 2nd example I switched to orthographic projection with the 
extends -4000000 -4000000 4000000 4000000. Projection center is lon=0 
and lat=0 and does not change in these examples (I know that this has to 
change every time the user performs a click. My client is able to handle 
this). This output looks ok to me.

If I enlarge the extend in example 3 the output picture is cut in the 
north south direction and I don't know why. I want to be able to enlarge 
the extent further so that the user thinks he "moves away" from the 
earth but pictures become smaller and smaller in north south direction 
when I enlarge the extent further (e.G.-6200000 -6200000 6200000 6200000)

Every extent that is "higher" than the earth radius (6378000) results in 
a blank image.

Can you help me here?

Thanks
Harald