Op 28/02/2021 om 14:54 schreef Kenneth:
> 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.
> 
> 
> 

Reorient_Trans, yes! That one I regularly use indeed. I must search my 
files where I apply it and whether I use the trace normal with it or not...

-- 
Thomas

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