OK, understood.

Or better I should say "almost". Now I understand the lens and the property parts... unfortunately I feel a bit dumb since I still not sure about the depth part. It sounds to me almost the same that the Z elevation, unless it refers to the elevation of the visitor's feet, for example. In such case I think the definition should be more precise about the size of the visitor instead use a vague term as "reasonable size". Anyway I think that I may not need the depth after all.

Thanks again, Emmanuel.