[MetaCRS] Z values & vertical datum transforms

[Richard Greenwood]

There has been a thread on the postgis list regarding changing the Z
value when a 3 or 7 parameter horizontal transform is done. This seems
totally wrong to me. In my mind horizontal and vertical datums, and
their associated transformations, are independent of each other.
1. What does the Z value returned by a cs2cs 3 or 7 parameter
horizontal transform represent?
2. Are there cases in which it is appropriate to apply this to
orthometric or ellipsoidal heights?
3. What's the general status of vertical transformations in Proj.4/cs2cs?

Thanks,
Rich

-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com