In article <3DD0220B.1B5F76C3@att.net>, LibraryMan <mrm### [at] attnet> 
wrote:

> POV choked on it!  AARRGGGH!  It's SO simple!  Why isn't it possible?!

It is possible, POV just choked because you gave it bad information. It 
is expecting a 2D vector in this case, you gave it a 3D vector. I'm not 
really sure what it would do in this case, either chop off the third 
component or give an error. Either way, it would not work...the third 
component is one you need. If you replace each "v_XX" with "< v_XX.x, 
v_XX.z>" it should work fine. If POV truncates 3D vectors to 2D ones, 
you just need to use coordinates in the xy plane and rotate around the z 
axis. I know that seems counterintuitive when the prism is in the xz 
plane.

Here are a couple macros that might be useful:

This macro truncates a vector to 2D, only useful if POV doesn't do it 
automatically:
#macro V2D(V) (<V.x, V.y>) #end
You would need to rearrange your vectors to be in the xy plane to use 
this macro. Or use this version:
#macro V_XZ(V) (<V.x, V.z>) #end

Another one, takes a 2D vector and angle to rotate it around the z axis:
#macro VRotate2D(V, A)
    #local Tmp = vrotate(V, z*A);
    (< Tmp.x, Tmp.y>)
#end

And if you are trying to get a perfect dodecagon, you are doing it the 
hard way...you could just use a loop:

#macro RegularPrism(Sides
    prism {linear_sweep linear_spline
        #local J = 0;
        #while(J < Sides)
            VRotate2D(<1, 0>, 360*J/12)
            #declare J = J + 1;
        #end
    }
#end

object {RegularPrism(12)
    pigment {color Green}
}

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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I did get it accepting the 2D vectors, as Chris had shown by forcing them
within the prism. I kept getting a 3D (or 4D or 5D?) when predeclaring even
with dot operators.

No dodecahedron (yet), so I leave that up to you to try and figure out.
Especially since I'm not sure what I'm doing with it. Chris's loop idea
sounds simpler but I couldn't get it to make one by rotating just the x
value, not with the loop he suggested though.

#declare v_01 =  <0.5, 0>;
#declare v_02 =  vrotate(<0.5, 0>,30*y);
#declare v_03 =  vrotate(<0.5, 0>,60*y);
#declare v_04 =  <0, -0.5>;
#declare v_05 =  vrotate(<0, -0.5>,30*y);
#declare v_06 =  vrotate(<0, -0.5>,60*y);
#declare v_07 =  <-0.5, 0>;
#declare v_08 =  vrotate(<-0.5, 0>,30*y);
#declare v_09 =  vrotate(<-0.5, 0>,60*y);
#declare v_10 =  <0, 0.5>;
#declare v_11 =  vrotate(<0, 0.5>,30*y);
#declare v_12 =  vrotate(<0, 0.5>,60*y);

prism {
linear_sweep
linear_spline
0, // sweep the following shape from here ...
1, // ... up through here
13, // the number of points making up the shape ...
<v_01.x,v_01.y>, <v_02.x,v_02.y>, <v_03.x,v_03.y>, <v_04.x,v_04.y>,
<v_05.x,v_05.y>, <v_06.x,v_06.y>, <v_07.x,v_07.y>,
 <v_08.x,v_08.y>, <v_09.x,v_09.y>, <v_10.x,v_10.y>, <v_11.x,v_11.y>,
<v_12.x,v_12.y>, <v_01.x,v_01.y>
pigment { color rgb <0,1,0> }
 rotate -90*x // face camera
}

camera {
 location -4*z
 look_at 0
}

light_source {
 <10,10,-10>,<1,0.5,1>
}
light_source {
 <-10,-10,-10>,<0.5,1,0.5>
}

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In article <3dd05985@news.povray.org>,
 "hughes, b." <omn### [at] charternet> wrote:

> No dodecahedron (yet), so I leave that up to you to try and figure out.

There's one in the include files.


> Especially since I'm not sure what I'm doing with it. Chris's loop idea
> sounds simpler but I couldn't get it to make one by rotating just the x
> value, not with the loop he suggested though.

The main problem was not with the loop, but with the prism statement, I 
didn't give a complete one. My excuse? I've never used the object 
before... ;-)
There was also a typo that would have made it work only with 12 sides, 
but that doesn't seem to be what you ran into.
I'm not sure what you mean by "rotating just the x value", unless you 
mean x as in < 1, 0, 0>.
This seems to work fine, with shorter code, and supporting any number of 
sides.

global_settings {assumed_gamma 1}

#declare CamPos = <-3, 2.5,-8>;
camera {
    location CamPos
    look_at < 0, 0, 0>
    angle 45
}

light_source {<-50,-50,-50>, color rgb 1}
light_source {CamPos, color rgb 0.05}

#macro VRotate2D(V, A)
    #local Tmp = vrotate(V, z*A);
    (< Tmp.x, Tmp.y>)
#end

#macro RegularPrism(Height1, Height2, Sides)
    prism {linear_sweep linear_spline
        Height1, Height2, Sides
        #local J = 0;
        #while(J < Sides)
            VRotate2D(x, 360*J/Sides)
            #local J = J + 1;
        #end
    }
#end

object {RegularPrism(0, 1, 12)
    pigment {color rgb 1}
    finish {ambient 0}
    rotate -x*45
}

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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On Mon, 11 Nov 2002 11:52:28 -0500, Johannes Dahlstrom quoth:

> hughes, b. wrote:
> 
>> A prism for a dodecahedron?
> 
> I think he meant a (extruded) regular 12-sided polygon. Don't know if it
> has an "official" name, but his guess, "dodecagon", sounds logical to
> me...
 
Yes, the name is "dodecagon".  Specifically, he wants a "right
dodecagonal prism".

-- 
Mark

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"LibraryMan" <mrm### [at] attnet> wrote in message news:3DC### [at] attnet...
> Correct, that is what I meant. :-)  "Dodeca-" I took to mean the prefix
> for twelve, and "gon" I thought would be the suffix for a multi-sided
> geometric shape.
> -MW
>
> Johannes Dahlstrom wrote:
> >
> > hughes, b. wrote:
> >
> > > A prism for a dodecahedron?
> >

www.tomandlu.co.uk/webres/misc/dodecahedron.wav

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"Christopher James Huff" <chr### [at] maccom> wrote in message
news:chr### [at] netplexaussieorg...
> In article <3dd05985@news.povray.org>,
>  "hughes, b." <omn### [at] charternet> wrote:
>
> > No dodecahedron (yet), so I leave that up to you to try and figure out.
>
> There's one in the include files.

Yes, I pointed that out before myself.  :-)

> > Especially since I'm not sure what I'm doing with it. Chris's loop idea
> > sounds simpler but I couldn't get it to make one by rotating just the x
> > value, not with the loop he suggested though.
>
> The main problem was not with the loop, but with the prism statement, I
> didn't give a complete one. My excuse? I've never used the object
> before... ;-)
> There was also a typo that would have made it work only with 12 sides,
> but that doesn't seem to be what you ran into.
> I'm not sure what you mean by "rotating just the x value", unless you
> mean x as in < 1, 0, 0>.
> This seems to work fine, with shorter code, and supporting any number of
> sides.

Yeah, that is great. Glad to see it can work that way, so thanks for
expanding on that scene script for it.

You misunderstood what I was saying, typing as I would speak there. I just
meant I hadn't even tried the loop and only did the prism like:

#declare v_01 =  <1, 0>;
#declare v_02 =  vrotate(<1, 0>,30*y);
#declare v_03 =  vrotate(<1, 0>,60*y);
...
#declare v_12 =  vrotate(<1, 0>,330*y);

which is the loop without the loop, I guess you could say, and got nothing
right from that. My mistake is apparently that I kept it using y instead of
z. I was *that* close! Oh well. Not my dodecagon anyway.  ;-)

Bob H.

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Christopher James Huff wrote:
> 

> And if you are trying to get a perfect dodecagon, you are doing it the
> hard way...

Well, I haven't gotten around to learning to use/write macros yet;  I
suspect much of the scene I'm working on could be done in more efficient
ways, coding-wise, but I'm just not up to reinventing that wheel yet...
;-)

--Library Man

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Christopher James Huff wrote:
> If you replace each "v_XX" with "< v_XX.x,
> v_XX.z>" it should work fine. 

It does, indeed!! Many thanks to all, even the ones who thought I was
trying to do a dodecaHEDRON! ;-)

--Mark ("LibraryMan")

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Christopher James Huff wrote:
> 

> 
> It is possible, POV just choked because you gave it bad information. It
> is expecting a 2D vector in this case, you gave it a 3D vector. I'm not
> really sure what it would do in this case, either chop off the third
> component or give an error. Either way, it would not work...the third
> component is one you need. If you replace each "v_XX" with "< v_XX.x,
> v_XX.z>" it should work fine. If POV truncates 3D vectors to 2D ones,
> you just need to use coordinates in the xy plane and rotate around the z
> axis. I know that seems counterintuitive when the prism is in the xz
> plane.


Just a point of info I'd like to clarify (or maybe I shouldn't open this
can of worms):

If I had declared only 2D vectors like so:
#declare v_01 = <0.5, 0>;  ... (rather than the 3D I used)

then would these be uv vectors, and would I be able to specify them in
the prism (or polygon, or conic sweep, or whatever) by using  [...]
<v_01.u, v_02.v>, <v_02.u, v_02.v>, etc. ?

I shouldn't get nit-picky, after all, what you specified using .x and .z
worked just fine.  I merely wanted to
see if I was understanding the manual correctly about uv vectors...

Thanks!
--Mark

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In article <3DD13CF9.CA8287AE@att.net>, LibraryMan <mrm### [at] attnet> 
wrote:

> Just a point of info I'd like to clarify (or maybe I shouldn't open this
> can of worms):
> 
> If I had declared only 2D vectors like so:
> #declare v_01 = <0.5, 0>;  ... (rather than the 3D I used)

I think this is the main problem...POV doesn't seem to support declared 
2D vectors, it seems to promote them to 3D. A language oddity that 
probably isn't worth fixing in 3.5, something to watch out for in 4.0.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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