Okay. This is all I could find in Traxx help about this topic:
The motives for using this feature have remained obscure until recently (Jan-Mar 2000). To date, the only way it's been used is to copy the terrain altitude from one track to another. Like this:
Access the copy terrain as bitmap feature by using one of the following
Following either of these procedures will copy the terrain bitmap to the windows clipboard.
Next, start a new track or open a track you have been working on and
paste the new terrain by using one of these methods:
Voila. The terrain for your track is exactly the same as the one
you just copied from.
Two additional techniques have been revealed that exploit the terrain bitmap in traxx.
The first is a way to reproduce exact portions of your track from one location to another. To do this, you would open the bitmap in a paint program and then copy and paste sections of it onto itself. Although I don't know anybody who's tried this trick, it might be an interesting shortcut that allows you to recreate a perfect curve without manually editing the terrain again and again. But, as I mention, I don't know of anyone who's had success doing this.
The second trick allows you to place models perfectly on top of ground
boxes or other places where you want them elevated over uneven terrain.
The idea was first brought to light by ObeOne
who suggested that copying the terrain to the clipboard (probably saving
it in a paint program as backup) allows you to temporarily flatten the
area you're working on so that you can place models with precision.
Then, once that's done, you can paste the original back in place, the result
being that the models are now suspended over the uneven terrain but with
perfect placement. You can see ObeOne's original post here.
adds notes about using this trick for better placement of extended courses
too. These are probably the most useful applications for the bitmap
feature. Thanks ObeOne and wk.