Thanks Brian! I'm on my phone so replied inline.

Each image is a sequential slice, of the 3D object,
separated by an increment of ____ mm, which determines the layer of the traced
2d object. (The example is using the front frame, x,z.)
-Yes (although front frame might be X, Y depending on coordinate system used)

Each image slice is loaded with the same x,z (or x,y?) position and (non)rotation.
-Yes

The image is "below" created objects? (or with objects or above objects?)
-Yes, image should be below.

The transparency setting is ___?
-Standard user controllable would be best


A slice is loaded, and the user traces a 2D object on the new layer.
-Yes

The previous 2D objects, (layers), need to be hidden?
-This should be an option. Sometimes this is not desirable, sometimes it is (also in a perfect world sometimes the previous layer geometry would be copied and left on the new layer, but this should be optional)

The user can flip back and forth between 2d object layers, or background slices,
to glean 3D help for the 2D trace.
-Yes, although layers are easy enough to handle, but perhaps layer visibility could be optionally linked to BG frame selected?

...
- Brian
EDITED: 10 Sep 12:17 by BEMFARMER