Thanks Gotz, helpful as ever.
!) and 3) I understand - thinking hybrid! In CAD, surfaces, vector-based plane shapes, and solids can be extend/trimmed together and can be inter-converted.
- a bit off topic but I see much talk of exif groupings - does that mean manual pre-sorting of the photo set into groups which share exif data which is identical for all exif categories? Or indentical just for certain optical catgories - f-stop, shutter speed, ISO, 35mm-equiv zoom, portrait/landscape, focus distance, flash or not - or what?