Am 14.05.2016 um 13:56 schrieb William F Pokorny:

> c) Looked too at the prism's use of splines and there too, as with
> lathes, the ordering of the point sets can flip the overall normals -
> for the prism's sides. An interesting sub-note here is that for some
> reason the prism-side's normal for the bezier splines are backwards from
> the other three spline types. The top and bottom of prism objects always
> face outward from the closed portions.

Can you distill this into a GitHub issue? I don't think this is how
things should be, but I currently don't have time to address it.

Thanks a lot for your quite exhaustive analysis!

> e) Due (c) & (d) I'd recommend leaving behavior as is for now and
> updating the documentation to make clear the spline point order has an
> effect of lathe and prism normals and differing inside and outside
> textures should be used if one needs to be sure how their shape is being
> interpreted.

If you want to go the extra mile, you could write up a suggested change
to the Docs as maintained on the Wiki (http://wiki.povray.org).

> f) I looked a little at the surface of revolution (SOR) object and it
> allows negative coordinates in x with a disclaimer, but enforces a rigid
> direction and ordering in Y.

Yes, that rigid Y ordering is the primary limitation of the SOR object
(I presume it predates the lathe).

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