"Kenneth" <kdw### [at] gmailcom> wrote:

> 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.

POV-Ray "measures" the normal of the surface that the ray intersects.
I'm pretty sure that there's no problem there.

Clearly understanding what those other macros actually do is probably where the
problem lies.

http://f-lohmueller.de/pov_tut/trans/trans_470e.htm

I must confess, things like this often become clear to me, and then I lose the
plot again a week later...

So if you have time and energy to do it, I'd copy those macros into scene files.
and then pick them apart, applying the parts step by step (if possible) and
understanding what the component operations actually do.

Pretend like you're explaining it to someone else, and document that in your
code.

A lot of what I've learned is due to digging into these really fundamental
things and writing scenes to illustrate them.  Because it confronts me with what
I don't know, and the consequences of my erroneous assumptions.

So I go from "I think I understand this"
to "I obviously have NO idea WTF I'm doing"
to "Well, that mostly works"
to "Oh - NOW I understand what's going on...."

And sometimes that may take me a day, a weekend, a week, a month, or in some
cases several years.

I'd look into vcross(), vdot(), and the order of rotations on a vector to move
it to properly align it with another vector.


https://www.youtube.com/watch?v=LyGKycYT2v0
https://www.youtube.com/watch?v=eu6i7WJeinw
https://www.youtube.com/watch?v=BaM7OCEm3G0
https://www.youtube.com/watch?v=Ip3X9LOh2dk

Not that I have _ever_ used quaternions before, but it does seem that they get
mentioned and used a lot, so maybe at some point I will muck around with those
for a bit.

https://www.youtube.com/watch?v=zjMuIxRvygQ

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