[postgis-users] Intersection Problem

[Christian Niemitz-Rossant]

Hi all,
we are dealing with a similar problem "The intersection of a 3D line and 
a 2D polygon returns a 3D line with some problems":

So far we got these results:
1. Points of the line inside the polygon (Z-projection) have the correct 
z-value which is simply unmodified.
2. The calculated intersection points of the line with the polygon have 
a z-value which is half of the expected result.
3. If the calculated intersection point has the same xy-coordinates as 
one point of the polygon then returned z-value is zero!

1. is fine, 2. is not really understandable but correctable by 
multiplying z-value with 2 and point 3 is sort of painful. We guess the 
projection to calculate the z-value doesn't work so the zero is returned.

We would appreciate hints, ideas or answers. Thanks!