Terrain at x,y gives same z value before and after a transformation is applied?

[JohnDavies]

Hello,

So here's the situation...  I have a terrain and using the "Add Surface Information" tool I added z values to a set of points that overlay the terrain.  Later I realized that the terrain was not lining up to my other data.  After lining up my terrain via a transformation I ran the "Add Surface Information" tool again only to see the exact same values.  So... My question is, when you run a geoprocessing tool like "Add Surface Info" are the coordinate systems somehow ignored and everything magically works no matter what projection/transformations have been applied and how does this work?

Thanks,

John

[TimBarnes]

Generally speaking, you should aim to do any sort of geoprocessing with all datasets projected to a common coordinate system to avoid these types of issues.

(I'm guessing here) but it is likely applying a default transformation to datasets it finds in different coordinate systems and, like many assumptions, this isn't always correct.