On 9/7/25 12:10, Bald Eagle wrote:
> According to the sor {} tutorial in the wiki:
> https://wiki.povray.org/content/ 
> Documentation:Tutorial_Section_3#Surface_of_Revolution_Object
> "First and last point from the list are used to determine slope at beginning and
> end of curve and can be defined for any height."
> 
> However, I find that to not be the case.
> Swapping the first and last control points causes a
> "Parse Error: Incorrect point in surface of revolution"
> But if I only set the LAST control point y value to zero, technically making the
> spline double-back in the y-direction, everything works fine.

First, Are you using v3.8 beta 2 for all your testing?

Second, Did you take care when you did the differences with the box to 
not have coincident surfaces with the caps (if there) or that y height 
when the caps are not there?

As to the point above, I don't see what you see. The following list 
works for me where I have flipped / crossed the first and last control 
points(*). See the attached image where the first is magenta and the 
last is yellow.

     <+1.5,+1.1> // C0
     <+0.4,0.0>  // C1
     <+0.3,0.5>  // C2
     <+0.4,0.9>  // C3
     <+1.5,+0.1> // C4

I'll try and look at some of the other issues you mention as I have 
time; Including temporarily removing the x>0.0 restriction on the first 
and last points to see what happens. Aside: we did remove a similar 
restriction for the lathe for v3.8 vs v3.7.

(*) I tried inverting all the on curve points and this does NOT work as 
I incorrectly remembered for some recent sor{} post - that must be a 
lathe{} only thing.

Bill P.

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