Orthographic Projection

Hi Friends

I need to implement orthographic Projection over an image generated by Mappoint webservice.

I am using the equations found on
Orthographic projection (cartography) - Wikipedia, the free encyclopedia

but it seems that it is not working. My first question is what is the value of the earth radius to be used in these equations? Must it be in m, km or other units?

any help is really appreciated.

regards

Im not sure of the answer to your question but I looked at this a while ago and come across this very usefull bit of code

Developing map projections with Java, the orthographic map projection

Its in Java but shouldn't be too hard to translate the useful bits into the language of your choice.

Thx, but what value I need to assign for R ?

Regards