Warp <war### [at] tagpovrayorg> wrote:
:   Funny, it describes the *right-handed* system using the *left-hand-metaphor*.

  The problem with this hybrid system is that it doesn't work if you try
to visualize the direction of rotations with your left hand.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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I have always thought of the x/y plane as being the sheet of graphpaper,
but that graph paper pasted up on the monitor. Therefore x is across the
monitor, y is up and down the monitor and z is out of the monitor, just like
it would be on that piece of graphpaper. To have it make sense to me, I use
right <-1.333,0,0> so that positive x is on the right, positive y is up and
positive z is towards me. I start of with my camera at +z, as if I were
looking down on the peice of graphpaper.

    Probably a really screwy way of doing it, but it makes sense to me.

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On Tue, 4 Dec 2001 15:20:45 -0500, Bill DeWitt wrote:
> 
>     Probably a really screwy way of doing it, but it makes sense to me.

Almost exactly what I do, except that I see z as into the monitor (i.e.
z increases as the distance from the viewer does) and so I use a left-handed
system (yours is right-handed.)

-- 
#local R=rgb 99;#local P=R-R;#local F=pigment{gradient x}box{0,1pigment{gradient
y pigment_map{[.5F pigment_map{[.3R][.3F color_map{[.15red 99][.15P]}rotate z*45
translate x]}]#local H=pigment{gradient y color_map{[.5P][.5R]}scale 1/3}[.5F
pigment_map{[.3R][.3H][.7H][.7R]}]}}}camera{location.5-3*z}//only my opinions

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"Ron Parker" <ron### [at] povrayorg> wrote in message
news:slr### [at] fwicom...
> On Tue, 4 Dec 2001 15:20:45 -0500, Bill DeWitt wrote:
> >
> >     Probably a really screwy way of doing it, but it makes sense to me.
>
> Almost exactly what I do, except that I see z as into the monitor (i.e.
> z increases as the distance from the viewer does) and so I use a
left-handed
> system (yours is right-handed.)

    But ... but.. how do you see through the graph paper?

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On Tue, 4 Dec 2001 16:19:42 -0500, Bill DeWitt wrote:
> 
> "Ron Parker" <ron### [at] povrayorg> wrote in message
> news:slr### [at] fwicom...
>> On Tue, 4 Dec 2001 15:20:45 -0500, Bill DeWitt wrote:
>> >
>> >     Probably a really screwy way of doing it, but it makes sense to me.
>>
>> Almost exactly what I do, except that I see z as into the monitor (i.e.
>> z increases as the distance from the viewer does) and so I use a
> left-handed
>> system (yours is right-handed.)
> 
>     But ... but.. how do you see through the graph paper?

I just use a sharpie to draw the lines right on the screen.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end 
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}

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"Ron Parker" <ron### [at] povrayorg> wrote :
> >
> >     But ... but.. how do you see through the graph paper?
>
> I just use a sharpie to draw the lines right on the screen.

    I've done that. Mostly marking positions during an animation.

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On Tue, 4 Dec 2001 16:27:34 -0500, Bill DeWitt wrote:
> 
> "Ron Parker" <ron### [at] povrayorg> wrote :
>> >
>> >     But ... but.. how do you see through the graph paper?
>>
>> I just use a sharpie to draw the lines right on the screen.
> 
>     I've done that. Mostly marking positions during an animation.

I usually use electrical tape for that; it comes off easier.  I taught
my son that trick for video games, too, so he'd know just exactly which
point on the screen to jump/shoot/whatever from when going up against 
some obstacle or other.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbt 1}hollow interior{media{emission T}}finish{
reflection.1}}#end Z(-x-x.2y)Z(-x-x.4x)camera{location z*-10rotate x*90}

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My math teacher projects graphs from her calculator onto a screen.  So y
is up and down and z is in and out.  But with our calculators on our
desks, y is toward and away from us and z is up and down.  I read
somewhere that the reason that POV-Ray uses the left-handed coordinate
system is because people are used to seeing graphs on boards and
pointing the y axis up.  But positive rotation is clockwise with POV and
counterclockwise with math classes.  So if POV-Ray adopted y as up, why
not positive rotation as being counterclockwise?  I hope that I'm wrong
about this otherwise there would be a self-contraction.
Brendan

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On Tue, 04 Dec 2001 20:31:12 -0500, Andrea Ryan wrote:
> pointing the y axis up.  But positive rotation is clockwise with POV and
> counterclockwise with math classes.  So if POV-Ray adopted y as up, why
> not positive rotation as being counterclockwise?  I hope that I'm wrong
> about this otherwise there would be a self-contraction.

Because POV also adopted z as into the screen, which is not how it works
in math.

--
#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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Ron Parker wrote:
> On Tue, 04 Dec 2001 20:31:12 -0500, Andrea Ryan wrote:
> > pointing the y axis up.  But positive rotation is clockwise with POV and
> > counterclockwise with math classes.  So if POV-Ray adopted y as up, why
> > not positive rotation as being counterclockwise?  I hope that I'm wrong
> > about this otherwise there would be a self-contraction.
>
> Because POV also adopted z as into the screen, which is not how it works
> in math.
>

When I was developing my person model (see it in p.b.a), I did the right
arm/leg and scaled it by <-1,1,1> to get the left.  What this means is that
when I'm figuring out the rotations for positioning the right side, I use my
left
hand, and when I'm figuring out the rotations for positioning the left side,
I use
my right hand.  Do you think I get confused?  You bet.

My point:  I need a point?

Tom Bates.

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