Unfortunately, I lack the minimum reputation required to pin images -- according to policy, the links below have been provided instead.
Here is the Figure I am addressing.
If it helps, this is the artist/architect's analysis of of the Figure.
This probably needs to be introduced with a modicum of background information: Andrea Pozzo was an artist/architect during the Baroque era in Italy. He specialized in quadratura, which exploits geometrical optics in order to distort dimensions (via different lines of sight).
The geometry and reference frames are (at first glance) straight forward; the angles/distances seem deliberate when observing the the diagram via rectangular coordinates. However,I am having a difficult time understanding "breaks in the cornice," -- this is due to the confusing perspectives created when analyzing the diagram via cylindrical coordinates.
Is there an apparent way to extrapolate the radii of these circles (which appear to tend toward zero as they approach the line of sight)? There appears to be substantial symmetry provided, yet I am not certain that we have enough information to determine the radii via geometrical axioms.
If there is a better way to formulate this question, please let me know (or perhaps point me toward some references).
Thanks.