How can i get the depth of Point(x,y)

I have the correct (x,y) value in world coordinate, i want to get the depth of the that point. How?

Heheh, if you have the world coordinates, you have everything. World coordinates are at the front of the transform stack.

the Point(x,y) which i got from the transformation of screen coord do not have correct z value. how can i get it?

Why don’t you check:

for gluUnProject()? It has the equation. I’d try to use that, but could be I’m wrong, as your posts are confusing.