Thomas de Groot <tho### [at] degrootorg> wrote:
> Op 27/02/2021 om 11:19 schreef Kenneth:
> [snip]
> > Btw, I'm using trace's returned surface NORMAL only as a 'switch'...
>
> I use trace pretty much like you; I don't remember where and if I got an
> example, but I am pretty sure you can use the surface normal generated
> by trace to positioning correctly the greebles an a slanted surface.
>

It would seem so-- but there's possibly *some* kind of problem (maybe 'problem'
is not the right word) for how trace creates its normal in the first place. But
I haven't exactly narrowed the problem down to trace itself; it may be in how
the normal is being 'processed' by other POV-ray tools in order to make use of
it.

I've once again been experimenting with two macros in "transforms.inc" that can
take a vector (like trace's NORM) and re-orient it to another vector direction:
Point_At_Trans, and Reorient_Trans. The latter seems to be a better and more
mathematically sophisticated version of the former. But when trace's returned
NORM is derived from particular curved or slanted surfaces, both of those macros
start to produce major changes to the expected 'orientation' of a placed object.
It's an old effect (plainly seen on a sphere, where there are entire 'quadrants'
of objects that switch direction.) This effect *may* even be by design(!), out
of mathematical/logical necessity. But it gets in the way :-( The maths used in
those macros are somewhat over my head, although I've tinkered with them, with
no satisfactory result.

So I rarely use trace's NORM normal anymore; too many unexpected headaches when
trying to actually use it.

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