We would really like to be able to upload landscape models and have the viewer limited so that it cannot go below the ground plane. Whether it be a house, roadway or other ground-based 3D model, having the object rotate so that you are "below ground" detracts greatly from the viewer experience we'd like to have. Is it possible to constrain rotation to avoid this? Similarly, I can see that it would be very helpful for some models to constrain rotation around another axis as well. Is there some tool or technique I'm unaware of to make this happen?