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Hi there,
I was wondering whether someone can explain the difference between a
spotlight and a cylindrical spotlight to me. The POV-Ray docs state:
> Cylindrical light sources work pretty much like spotlights
> except that the light rays are constrained by a cylinder
> and not a cone.
> .....
> You should keep in mind that the cylindrical light source
> is still a point light source. The rays are emitted from
> one point and are only constraint by a cylinder. The
> light rays are not parallel.
If the rays are not parallel and contrained by a cylinder, how is this
different from a spotlight constrained by a cone?
Does this mean that the area illuminated by the light is the same no
matter how far away the surface is? If so, then why do the docs say
that the rays are not parallel?
Confused,
- Lutz
email : lut### [at] stmuc com
Web : http://www.stmuc.com/moray
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Lutz Kretzschmar wrote:
>
> If the rays are not parallel and contrained by a cylinder, how is this
> different from a spotlight constrained by a cone?
> Does this mean that the area illuminated by the light is the same no
> matter how far away the surface is? If so, then why do the docs say
> that the rays are not parallel?
>
It does mean that the area illuminated by the light is the same no
matter how far away the surface is. However, the rays are not parrallel:
the shadow of an object is the same as if you had a pointlight (or a
spotlight), that is bigger when farther away whereas true parallel rays
would make the same shadow no matter what distance the object is from
the light position and shadow position. Nathan Kopp's uvpov includes a
patch for true cylindrical light (Idon't know about the superpatch).
Jerome
--
*******************************
* they'll tell you what can't * mailto:ber### [at] inamecom
* be done and why... * http://www.enst.fr/~jberger
* Then do it. *
*******************************
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The Superpatch contains a parallel light patch which works for all kinds
of lights, instead of simply modifying the cylinderical light. There are
also a bunch of other interesting patches for the light sources in
there.
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Is that the same parallel light patch that is part of UVpov - or something
entirely different? I have used the parallel light patch in UVpov, but have
encountered a bug that is fairly major (see my posting in p.u.n.).
Chris Huff wrote:
> The Superpatch contains a parallel light patch which works for all kinds
> of lights, instead of simply modifying the cylinderical light. There are
> also a bunch of other interesting patches for the light sources in
> there.
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I don't think it is related to the one in UVPov, but I might be
mistaken. It is certainly a lot different than the one in UVPov.
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How long has it been part of Superpatch?
Chris Huff wrote:
> I don't think it is related to the one in UVPov, but I might be
> mistaken. It is certainly a lot different than the one in UVPov.
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On Sat, 23 Oct 1999 01:28:06 -0700, Tony Vigil wrote:
>How long has it been part of Superpatch?
>
>Chris Huff wrote:
>
>> I don't think it is related to the one in UVPov, but I might be
>> mistaken. It is certainly a lot different than the one in UVPov.
I'm pretty sure it's a different patch. It's from xenoarch, not from
Nathan; it came along with the projected_through and the light groups
patches. It's been in there since the 3.1d release.
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