I just wanted to know the best way to make a laser. I was told to use
area lights, but it doesn't occur to me how that could work. I need the
light intensity and the width of the beam to remain almost constant and
for it to be seen from the side. I saw how to do it in 3D Studio Max,
but that doesn't help.
Also, can I make a halfway mirror that reflects on one side but is
transparent from the other side?

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"Stan" <swr### [at] earthlinknet> wrote in message
news:39978544.2D5317BF@earthlink.net...
| I just wanted to know the best way to make a laser. I was told to use
| area lights, but it doesn't occur to me how that could work. I need the
| light intensity and the width of the beam to remain almost constant and
| for it to be seen from the side. I saw how to do it in 3D Studio Max,
| but that doesn't help.

I kind of tried and failed at making the perfect laser beams in MegaPov.
It's possible to get a single beam for sure, no problems there, just use
media contained within a cylinder along with a cylidrical light source.

| Also, can I make a halfway mirror that reflects on one side but is
| transparent from the other side?

I even had the laser beaming out from behind a 100% (+/- a fraction of
percent) mirror, diagonal to the beam.  Orientation not really a concern
though.  I had used the mirror and beam together as a 'looks_like' within
the light source.  That way there isn't any self shadowing so the beam
shines through unaffected.  However when it comes to bouncing the beams
around in the media that's where I was stopped.  Someone else might have the
answer to it.  This is why I had to go with multiple beams and just faked
the reflected light.

Bob

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In article <39978544.2D5317BF@earthlink.net>, Stan 
<swr### [at] earthlinknet> wrote:

> I just wanted to know the best way to make a laser. I was told to use
> area lights, but it doesn't occur to me how that could work. I need the
> light intensity and the width of the beam to remain almost constant and
> for it to be seen from the side. I saw how to do it in 3D Studio Max,
> but that doesn't help.

Area lights wouldn't be very useful for lasers...try using cylinderical 
lights. Even better would be to use the cylinderical lights of MegaPOV, 
which have been slightly fixed so the light rays are parallel instead of 
originating from a point.
To get the beam to be visible from the side, you will need to add 
scattering media to the scene. Just make a container object which 
encloses your whole scene, it is usually easier to adjust and more 
reliable than global media.
If you want to have your laser beam bouncing off of reflective objects 
or being bent by prisms or lenses, you will need to use MegaPOV's photon 
mapping feature. I think there is a demo of a laser scene 
somewhere...but I may be confusing the demo scenes with something from 
these newsgroups.


> Also, can I make a halfway mirror that reflects on one side but is
> transparent from the other side?

This is easiest to do in MegaPOV, which has an interior_texture feature 
which allows you to give the "inner" surface of a shape a different 
texture from the outer surface. Note that all shapes, even triangles, 
have two sides.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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On Sun, 13 Aug 2000 22:36:05 -0700, Stan <swr### [at] earthlinknet>
wrote:

>I just wanted to know the best way to make a laser. I was told to use
>area lights, but it doesn't occur to me how that could work. 

That's because area_lights are not the solution <grin>

The best way to do it is to use the true cylinder lights available in
MegaPOV. Or parallel_lights with projected_through, in MegaPOV again.

>I need the light intensity and the width of the beam to remain almost 
>constant and for it to be seen from the side. 

What I am proposing will keep them 100% constant. To make it diverge a
bit you'll have to use distant a spotlight (or pointlight) with
projected_through. And if you want it to be visible, make sure there's
something to reflect it, i.e. dust (read: scattering media).

You can also fake it with a transparent hollow cylinder filled with
emitting media.

>Also, can I make a halfway mirror that reflects on one side but is
>transparent from the other side?

I am just guessing here but I think the interior_texture feature in
MegaPOV can do this.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

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> This is easiest to do in MegaPOV, which has an interior_texture feature
> which allows you to give the "inner" surface of a shape a different
> texture from the outer surface. Note that all shapes, even triangles,
> have two sides.
What about an isosurface representing a mobius-ring?

ZK
http://www.povplace.be.tf

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In article <39981ff8@news.povray.org>, "Zeger Knaepen" 
<zeg### [at] yahoocom> wrote:

> What about an isosurface representing a mobius-ring?

Make one. :-)
The only way you can do it with an isosurface would either give the 
strip thickness, so it would have an internal side and an external side, 
or leave a discontinuity where the normal flips.

It should be possible with the parametric shape, in which case I think 
there will still be a discontinuity at the point the beginning and end 
meet. That, or it will always show the "outside" texture. I don't know 
how the parametric calculates normals.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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Wasn't it Stan who wrote:

>Also, can I make a halfway mirror that reflects on one side but is
>transparent from the other side?

In MegaPOV you can use "interior_texture" to have different textures on
different sides of the same surface. E.g. you can declare the texture of
(a part of) a plane to be reflective, and the interior_texture to be
transparent.

-- 
Mike Williams
Gentleman of Leisure

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Wasn't it Chris Huff who wrote:
>In article <39981ff8@news.povray.org>, "Zeger Knaepen" 
><zeg### [at] yahoocom> wrote:
>
>> What about an isosurface representing a mobius-ring?
>
>Make one. :-)
>The only way you can do it with an isosurface would either give the 
>strip thickness, so it would have an internal side and an external side, 
>or leave a discontinuity where the normal flips.
>
>It should be possible with the parametric shape, in which case I think 
>there will still be a discontinuity at the point the beginning and end 
>meet. That, or it will always show the "outside" texture. I don't know 
>how the parametric calculates normals.
>

There's a parametric Moebius strip in my isosurface tutorial (about half
way down page <http://www.econym.demon.co.uk/isotut/parametric.htm>)

Adding an interior_texture clause to this object causes a discontinuity
of texture on the right hand side. It's exactly as if you had taken a
piece of paper that was coloured differently on each side, twisted it,
and stuck it together.

                               
#declare R=1.3;

#declare Fx = function {cos(u)+v*cos(u/2)*cos(u)}
#declare Fy = function {sin(u)+v*cos(u/2)*sin(u)}
#declare Fz = function {v*sin(u/2)}
                        
#declare U1 = 0;
#declare U2 = 2*pi;
#declare V1 = -0.3;                       
#declare V2 = 0.3;

parametric {
  function Fx(u,v,0),  Fy(u,v,0),  Fz(u,v,0)
      <U1,V1>,<U2,V2>
      <-R,-R,-R>,<R,R,R>
  accuracy 0.001
  precompute 18, [x,y,z]
  texture {pigment {rgb <1,1,0>}}
  interior_texture {pigment {rgb <0,1,1>}}
  finish {phong 0.5 phong_size 10}
  no_shadow
}

What's actually happening is that MegaPov doesn't actually know that the
ends of the strip actually meet. It treats it as an ordinary two sided
surface. 

If you change the range of the "u" parameter to, say, U1=0 U2=2*pi-0.1
then you can see that you've got a twisted piece of paper that comes 0.1
radians short of making a ring, and the colour change is at the gap.

The colour change can be made to occur anywhere on the ring by adjusting
the range of the "u" parameter. E.g. if you add 1 to both U1 and U2 then
the colour change is shifted 1 radian anticlockwise round the ring.

If you change the range of the "u" parameter so that it runs twice round
the ring, then the two textures both run round the ring twice and
interfere with each other.

If you change "u" and "v" to 
  #declare U1 = 0;
  #declare U2 = 4*pi;
  #declare V1 = 0;                       
  #declare V2 = 0.3;
and you get the texture discontinuity in the "v" direction instead of
the "u" direction.

-- 
Mike Williams
Gentleman of Leisure

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