Gerald,
[...] I made the change and it seems to work fine as long as "maintain screen coordinates" is set to yes. [...]
Are there any problems when it is set to "no"? I thought it was supposed to keep screen and image coordinates synchronised in that case.
No, it seems more logical to me, though, to maintain the screen coordinates while zooming the image coordinates.
I need to make it easier to zoom the screen size, since it has to be done by hand now.
Played around with those screen/image orbit features a bit and tended to do the following:
Zooming in with "maintain..." set to no. Finding an interesting place, but wanting to move or zoom in/out the image coordinates alone...
Now, switching to yes would revert the screen coordinates I want to keep.
Ach! It's not meant to do that. I'll have to take a look to see what has happened. You should be able to switch from one mode to the other without any change in either set of coordinates. I'll have a chance to look at it on Sunday. Jonathan