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On 4/10/2016 2:28 PM, Bald Eagle wrote:
> Stephen <mca### [at] aol com> 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.
>
When I used to work for a living. I've used both for different parts of
the job and polar coords as well. People just assume that everyone uses
the one they're using.
Using Moray (Z-up) as a modeller then modifying the code in PovRay
showed me a number of ways how to mess up.
> 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.
>
I thought a "corner of a cardboard box" was a good idea. And a pencil
and rubber comes in handy too.
I think Excel spreadsheets are the best thing since sliced bread. I
start a new one for each project.
>> 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.
>
Sorry, I was being flippant. Don't take everything I say seriously.
Polar is very useful and you need to be able to switch between them when
it is easier.
And that is not laziness it is common sense. I create things in unions
at the origin. As I don't have direct access to the code until its
exported. Having an extra union gives me a local set of axles.
> 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
No need to be so formal. :-)
>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.
>
Oo! I don't know. I would say that once you get it working. Leave it
alone. If it breaks next year, fix it then. :-)
I am only joking, I think. But then I can't code so maybe I'm not. :-)
> “What are the facts? Again and again and again – what are the facts? Shun
> wishful thinking, ignore divine revelation, forget what “the stars foretell,”
> avoid opinion, care not what the neighbors think, never mind the unguessable
> “verdict of history” – what are the facts, and to how many decimal places? You
> pilot always into an unknown future; facts are your single clue. Get the facts!”
>
> ― Robert A. Heinlein
>
>
TO WOUND THE AUTUMNAL city.
So howled out for the world to give him a name.
The in-dark answered with wind.
All you know I know: careening astronauts and bank clerks glancing at
the clock before lunch; actresses cowling at light-ringed mirrors and
freight elevator operators grinding a thumbful of grease on a steel
handle; student riots; know that dark women in bodegas shook their heads
last week because in six months prices have risen outlandishly; how
coffee tastes after you’ve held it in your mouth, cold, a whole minute.
Dhalgren
Samuel Delany
--
Regards
Stephen
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"Bald Eagle" <cre### [at] netscapenet> wrote:
> "SecondCup" <nomail@nomail> wrote:
> > Thanks to everyone for the advice and suggestions. I got it to do exactly what I
> > wanted. Happy days.
>
> Congrats! :) I'm happy it's all working out for you.
> Sometimes you just need enough of a nudge over some "threshhold", and then it
> all clicks into place after that.
>
> > Once you get the hang of the coordinate system, building a spline is the way to
> > go for smooth animations.
>
> There are indeed many uses for splines, and there are all sorts of neat little
> tricks and things that people have come up with. Heck, there's SO much stuff
> in just the documentation that most of the time it's hard to even know what to
> do with it all!
>
> Be sure to check out http://www.f-lohmueller.de/ as well. He's put a LOT of
> work into posting very useful working code and tutorials.
I've got http://www.f-lohmueller.de/ to thank for getting me to where I am in
less than a month!
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On 11-4-2016 2:31, Stephen wrote:
>>
> TO WOUND THE AUTUMNAL city.
> So howled out for the world to give him a name.
> The in-dark answered with wind.
> All you know I know: careening astronauts and bank clerks glancing at
> the clock before lunch; actresses cowling at light-ringed mirrors and
> freight elevator operators grinding a thumbful of grease on a steel
> handle; student riots; know that dark women in bodegas shook their heads
> last week because in six months prices have risen outlandishly; how
> coffee tastes after you’ve held it in your mouth, cold, a whole minute.
>
> Dhalgren
>
> Samuel Delany
>
Yes. Somehow, this has to be mentioned once in a while. Again and again.
Until they misunderstand.
--
Thomas
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On 11-4-2016 1:09, Stephen wrote:
> On 4/10/2016 3:37 PM, clipka wrote:
>> Am 10.04.2016 um 15:00 schrieb Stephen:
>>> On 4/10/2016 1:37 PM, Bald Eagle wrote:
>>>> The coordinate system is a static "thing" It doesn't "do" anything.
>>>> Look_at just determines what direction the camera is pointing when
>>>> it's at a
>>>> given location ("vector").
>>>
>>> Just one thing to mention. There are two coordinate systems*, Y up and Z
>>> up. Depends if you are a mathematician or an engineer. Moray used Z up.
>>> There is also left hand and right hand versions too.
>>> 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.
>>
>> In other words, you refer to cartesian coordinates only.
>>
>> Well, actually there are only _two_ fundamentally different
>> 3-dimensional cartesian coordinate systems: A right-handed one and a
>> left-handed, and _infinitely_ many different orientations of those two
>> coordinate systems, each of which are equally valid from a mathematical
>> point of view.
>>
>> So accomodating only for the handedness and a choice of whether Y or Z
>> is up doesn't quite cut it.
>>
>
> Well it confused me going from Moray's Y up to PovRay's Z up coordinate
> system. It is easy to make a mistake. It was also the source of many a
> flame war, years ago.
> A 2D X-Y plane is looked down on like a piece of paper by mathematicians
> and Z is up/height. Whilst Engineers looked into an oscilloscope and Z
> is depth. Or the other way around. Lutz of Moray fame wouldn't hear talk
> about it.
> It is a simple transformation to convert and I know for a fact Thomas
> has memorised it.
It's a mantra.
>
> So what doesn't cut what?
> I don't understand.
>
--
Thomas
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On 4/11/2016 7:59 AM, Thomas de Groot wrote:
>
> Yes. Somehow, this has to be mentioned once in a while. Again and again.
> Until they misunderstand.
That sounds like a quote. Is it?
--
Regards
Stephen
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On 11-4-2016 12:57, Stephen wrote:
> On 4/11/2016 7:59 AM, Thomas de Groot wrote:
>>
>> Yes. Somehow, this has to be mentioned once in a while. Again and again.
>> Until they misunderstand.
>
>
> That sounds like a quote. Is it?
>
I wanted it to look like a quote ;-)
--
Thomas
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Thomas de Groot <tho### [at] degrootorg> wrote:
> Yes. Somehow, this has to be mentioned once in a while. Again and again.
> Until they misunderstand.
>
> --
> Thomas
So then with respect to the coordinate system:
One through nine, no maybes, no supposes, no fractions. You can't travel in
space, you can't go out into space, you know, without, like, you know, uh, with
fractions - what are you going to land on - one-quarter, three-eighths? What are
you going to do when you go from here to Venus or something? That's dialectic
physics.
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On 4/11/2016 12:13 PM, Thomas de Groot wrote:
> On 11-4-2016 12:57, Stephen wrote:
>> On 4/11/2016 7:59 AM, Thomas de Groot wrote:
>>>
>>> Yes. Somehow, this has to be mentioned once in a while. Again and again.
>>> Until they misunderstand.
>>
>>
>> That sounds like a quote. Is it?
>>
>
> I wanted it to look like a quote ;-)
>
I just stole the first few lines from a book that starts where it
finishes off.
If you have not read Dhalgren. It is experimental, strangely structured
and unearthly. Full of sex and drugs and street biker/hippy gangs in a
post apocalyptic city. A strange book, the underbelly of science fiction
but artistic too.
--
Regards
Stephen
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On 11-4-2016 13:34, Stephen wrote:
> I just stole the first few lines from a book that starts where it
> finishes off.
> If you have not read Dhalgren. It is experimental, strangely structured
> and unearthly. Full of sex and drugs and street biker/hippy gangs in a
> post apocalyptic city. A strange book, the underbelly of science fiction
> but artistic too.
>
Oh, I know Dhalgren and it is one of my favourites.
--
Thomas
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On 11-4-2016 13:12, Bald Eagle wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>
>> Yes. Somehow, this has to be mentioned once in a while. Again and again.
>> Until they misunderstand.
>>
>> --
>> Thomas
>
> So then with respect to the coordinate system:
> One through nine, no maybes, no supposes, no fractions. You can't travel in
> space, you can't go out into space, you know, without, like, you know, uh, with
> fractions - what are you going to land on - one-quarter, three-eighths? What are
> you going to do when you go from here to Venus or something? That's dialectic
> physics.
>
Well, my pseudo quote was about Stephen's Dhalgren quote but it is
possible to use it for the coordinate system too :-) So, yes.
--
Thomas
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