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I still don't quite get why math (and hence POV) 3D coords use
left-hand rule; apart from most people being right-handed, CAD
programs use right-hand, being based on architectural design which
draws a floorplan along the XY plane with Z being the elevation,
which is what you get when you draw a floorplan on a standard
cartesian grid with 0,0 being the origin in the lower-left.
--
Tim Cook
http://empyrean.scifi-fantasy.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
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"Timothy R. Cook" wrote:
>
> I still don't quite get why math (and hence POV) 3D coords use
> left-hand rule;
Because when you have the pencil in the right hand, only
the left hand is available for fancy manipulation !
Moreover, on computer, you need the right hand for the numeric pad.
(especially when typing pov-vector in script)
And last: Pov is not left-handed. It is half-ambidextrous* :
default to left hand, but can work without problem with right hand.
* half-ambidextrous: just similar to half-duplex, can be both but not
at the same time.
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"Timothy R. Cook" wrote:
>
> I still don't quite get why math (and hence POV) 3D coords use
> left-hand rule; apart from most people being right-handed, CAD
> programs use right-hand, being based on architectural design which
> draws a floorplan along the XY plane with Z being the elevation,
> which is what you get when you draw a floorplan on a standard
> cartesian grid with 0,0 being the origin in the lower-left.
>
It's no problem at all to do right-handed geometry in POV, just have a
look at what Moray generates for example.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
IsoWood include, radiosity tutorial, TransSkin and other
things on: http://www.schunter.etc.tu-bs.de/~chris/
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Christoph Hormann wrote:
> It's no problem at all to do right-handed geometry in POV,
One may represent the three axes as they appear in povray with one's right
hand, but your coworkers and family members would complain about you
flipping them the bird.
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On Tue, 04 Dec 2001 07:06:15 -0500, Timothy R. Cook wrote:
> I still don't quite get why math (and hence POV) 3D coords use
> left-hand rule; apart from most people being right-handed, CAD
Math uses the right-hand rule too. POV uses the left-hand rule by
default because that's how it was created. Call it a historical
accident. To change it now would just be wrong.
--
#macro R(L P)sphere{L __}cylinder{L P __}#end#macro P(_1)union{R(z+_ z)R(-z _-z)
R(_-z*3_+z)torus{1__ clipped_by{plane{_ 0}}}translate z+_1}#end#macro S(_)9-(_1-
_)*(_1-_)#end#macro Z(_1 _ __)union{P(_)P(-_)R(y-z-1_)translate.1*_1-y*8pigment{
rgb<S(7)S(5)S(3)>}}#if(_1)Z(_1-__,_,__)#end#end Z(10x*-2,.2)camera{rotate x*90}
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"Greg M. Johnson" wrote:
> One may represent the three axes as they appear in povray with
> one's right hand, but your coworkers and family members would
> complain about you flipping them the bird.
...actually I never understood why people even needed to
represent the axes with their hand except for demonstrating
to people who didn't know about them; I have no trouble
picturing the axes in my head.
--
Tim Cook
http://empyrean.scifi-fantasy.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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"Timothy R. Cook" <tim### [at] scifi-fantasycom> wrote :
>
> ...actually I never understood why people even needed to
> represent the axes with their hand
It's a learning tool... there was a time when you needed to learn it
too, whether you remember it or not.
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On Tue, 04 Dec 2001 08:37:14 -0500, Timothy R. Cook wrote:
> "Greg M. Johnson" wrote:
>> One may represent the three axes as they appear in povray with
>> one's right hand, but your coworkers and family members would
>> complain about you flipping them the bird.
>
> ...actually I never understood why people even needed to
> represent the axes with their hand except for demonstrating
> to people who didn't know about them; I have no trouble
> picturing the axes in my head.
The "right hand rule" is most useful for visualizing which way a
cross product (or, by extension, a rotation) goes. If you can do that
in your head, great, but many otherwise talented people can't.
--
plane{-z,-3normal{crackle scale.2#local a=5;#while(a)warp{repeat x flip x}rotate
z*60#local a=a-1;#end translate-9*x}pigment{rgb 1}}light_source{-9red 1rotate 60
*z}light_source{-9rgb y rotate-z*60}light_source{9-z*18rgb z}text{ttf"arial.ttf"
"RP".01,0translate-<.6,.4,.02>pigment{bozo}}light_source{-z*3rgb-.2}//Ron Parker
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"Timothy R. Cook" <tim### [at] scifi-fantasycom> wrote in message
news:3C0CD18A.968961E9@scifi-fantasy.com...
>I have no trouble
> picturing the axes in my head.
>
Sounds painful, have you been arguing with Bill?
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> And last: Pov is not left-handed. It is half-ambidextrous* :
> default to left hand, but can work without problem with right hand.
This isn't quite true. Lots of the primitives have the y-axis hardcoded as
the "vertical" axis.
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