Stephen <mca### [at] aolcom> wrote:
> On 4/10/2016 1:37 PM, Bald Eagle wrote:

> Just one thing to mention. There are two coordinate systems*, Y up and Z
> up.

Right.  I've use right-handed, z-up, and it did, for whatever strange human
reason, take a bit of getting used to when I started using POV's left-handed
y-up system.

But some days (nights) _nothing_ makes sense, and that's why drawing things out,
and checking both the math and _the assumptions_ you are progressing from, are
always a good idea.
I use lots of paper, Excel spreadsheets, unit circle diagrams, 3D space models
or diagrams, test renders, etc.

> One of the reasons I use a modeller I cannot visualise scenes well
> enough to be a true Pover.

> * Not counting all the fancy ones like Polar, Plücker, cylindrical etc.

I wouldn't really call polar "fancy" - especially since I often find it easier
on the brain to "be lazy" and do the ole' define an object at the origin,
translate, then rotate.   Saves doing a lot of trig to get the coordinates,
especially if I'm not just rotating in one plane, but then tilting up into "3D".
   Cylindrical is just polar with an "altitude" (z) thrown in.

Plucker looks like something clipka might be well familiar with.   I have a
feeling he's got a way better handle on all of that affine geometric stuff than
I've got.

But yes, SecondCup - you should take Mr. McAvoy's advice and make sure that your
assumptions about your axes are correct.   That has caused me, and many other
POV-ers way too many unnecessary headaches.   I've even done it when I KNEW I
wanted to be avoiding it.   So write it down, calculate it, and graph it out.
Don't just let your code fly into uncharted territory - nail down your FACTS,
and double and triple check what you're doing until you get it to work out
correctly.   Then - just for fun, and as a test of how robust your code is,
change some things around a bit.   Add in things like negative values, zero,
very large values, etc. to see how robust your system is, and to make sure that
you're not just in some little coincidental mathematical bubble.



avoid opinion, care not what the neighbors think, never mind the unguessable



― Robert A. Heinlein

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