I remember reading somewhere that a number of things in POVRay are "faked"
for speed considerations.

Could someone please tell me which things are faked, and how the "fake"
implementaion differs from a "real" one?

Rohan _e_ii

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Well, there's phong and specular highlighting. In RL, highlights
are caused by reflections of very, very, very, very,... bright
objects. So, even though you could somehow simulate this
effect with exponential reflection and high-rgb/ambient objects,
that would be pretty slow.

AFAIK brilliance is also a crude model, but I'm not too sure about
that.

Arealight is faked, it only creates soft shadows, but no soft
highlights etc.

iridiscence is just an approach to model thin film interferences and
isn't based on any realistic model (again, AFAIK), but has enough
options so that you can tweak it till realistic results.

Fog and rainbow-fog are just distance-based color-modifiers (or
something like that :-) and don't interact with light as real
fog would.

There's problably more, but that's all I can think of right now.

Oh, and don't forget the checkered plane, in RL, no one
would be insane and create a tiled floor that big. ;-)

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


> I remember reading somewhere that a number of things in POVRay are "faked"
> for speed considerations.
>
> Could someone please tell me which things are faked, and how the "fake"
> implementaion differs from a "real" one?
>
> Rohan _e_ii
>


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Rohan Bernett <rox### [at] yahoocom> wrote:
> I remember reading somewhere that a number of things in POVRay are "faked"
> for speed considerations.

> Could someone please tell me which things are faked, and how the "fake"
> implementaion differs from a "real" one?

  Everything in POV-Ray is faked.
  No matter what you do, you can only approximate what happens in reality.

  The idea in that claim may be that some things are approximated more
accurately than others.
  For example, making the approximation that direct diffuse illumination
is relative to the cosine of the surface normal and the direction of the
light is pretty accurate. Approximating an area light source with a grid
of point lights is a quite rough approximation (but looks good enough).

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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> I remember reading somewhere that a number of things in POVRay are "faked"
> for speed considerations.
>
> Could someone please tell me which things are faked, and how the "fake"
> implementaion differs from a "real" one?


The most significant "faked" thing in POV-Ray is the behavior of light. In
real life, a light source (such as the sun) emits light, which hits objects,
and then bounces into our eyes. In POV-Ray (and practically every other 3D
program), paths are traced from the eye of the camera onto objects, and then
checked to see if the path to the light source is clear. If so, color is
drawn there. This is why it's called "backwards raytracing" - because we
trace the path of light backwards, instead of forwards. This saves time
because we avoid tracing light rays that don't hit the camera.

This has its limitations, which POV-Ray works to overcome through Photons
and Radiosity. Photons are a way of tracing the light forwards, from the
light source outwards, but only in the directions which are going to make a
noticeable difference in the scene. Radiosity is still essentially a
backwards simulation, but it attempts to replicate the bouncing-around of
light which causes shadowed areas to be lit up, depending on how much light
is reaching them in an indirect manner.

 - Slime
[ http://www.slimeland.com/ ]

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