I have been doing my memory-drawing exercises with a twist: I try to draw things rotated from imagination. This also forces me to understand the underlying simplified 3D forms and to come up with the details you only see from other angles.
I found that my set of reference images , where you see the same thing from different angles, is really useful for that, because you can first try to draw something rotated from imagination, and then verify and correct your drawing based on a photo of the rotated version.
For that purpose, I have been expanding the set of statues I have photographed. Strangely, I had been photographing statues in other cities, but not in the city I live in! You can see the new set of statues here.
I made a big mistake at the museum: the shutter speed was set far too fast, forcing the camera to use a higher ISO, which resulted in far more noise in the photos than necessary. I'll have to go back to fix that.
I already gave many statues and objects the same treatment before.
The 3D models are also suitable for this exercise. They might be more suitable for beginners as they are simpler and provide the building blocks for doing this later with more complex references.
Yours sincerely,