Hi Dave,

I am at work so I can't test it right now, but just reading through that
file it looks like you do have coincident surfaces going on with the base
of the cone and the plane. The cone has its base at <0, 0, 0> which is then
translated to <-8, -1, 17>, while the plane is defined at y = -1.

Either move the cone up a small amount:
cone
{
  <0,0,0>, 5.5, <0,11,0>, 0
  translate <-8, -1, 17>
  translate 0.01*y /* add this line to move the cone up from the plane */
  texture {
    ...
  }
  ...
}

Or move the plane down:
plane
{
  y, -1
  texture
  {
    ...
  }
  translate -0.01*y /* add this line to move the plane down from the cone */
}


I will have a closer look when I get home, but I think this might be it?

-- sooperFoX


"NetDave" <new### [at] netdavecom> wrote:
> I posted  the a sample of the code that demonstrates the problem in
> p.b.scenefiles. I'm using the current POV release. I noticed that if I
> translate the cone a towards the foreground, the speckles seem to diminish,
> but that doesn't solve my question.

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See my responses below.

"sooperFoX" wrote:
> Hi Dave,
>
> I am at work so I can't test it right now, but just reading through that
> file it looks like you do have coincident surfaces going on with the base
> of the cone and the plane. The cone has its base at <0, 0, 0> which is then
> translated to <-8, -1, 17>, while the plane is defined at y = -1.


I can confirm this now. I get the same result as you when rendering your
scene unmodified.


> Either move the cone up a small amount:
> cone
> {
>   <0,0,0>, 5.5, <0,11,0>, 0
>   translate <-8, -1, 17>
>   translate 0.01*y /* add this line to move the cone up from the plane */
>   texture {
>     ...
>   }
>   ...
> }


Tried this. See first attached image. No speckles now, but a large black
area appears in the lower region of the cone.

I assumed this had something to do with max_trace_level, so I increased it
to 255 (outside the photons block). This didn't really remove the black
area but I got some more internal reflections happening now. See second
image.


So then I tried something I remember reading when I was messing around with
water inside a drinking glass - putting the surfaces inside each other
rather than separate. So, I moved the cone *down* slightly (translate
-0.01*y) instead of up, and bingo. See the third image. I think this is
what you're after, no?


-- sooperFoX

EDIT: second and third images will have to go in subsequent posts, because I
can't seem to attach more than one at a time through the web interface.

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Attachments:
Download 'cone-photons-trans.jpg' (26 KB)

Preview of image 'cone-photons-trans.jpg'

Image 2/3:
Illustrates global_settings { max_trace_level 255 } with cone translated
*up* away from the plane.

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Attachments:
Download 'cone-photons-trans-255.jpg' (29 KB)

Preview of image 'cone-photons-trans-255.jpg'

Image 3/3:
This image illustrates translating the cone *down* into the plane,
essentially removing the lower surface of the cone.
The photons are now visible on the plane (rather than being obscured by the
total internal reflections when the bottom of the cone is visible).

Also I forgot to add that doing this increased the render time significantly
(still, only about 16 minutes at 960x600, including photon building), but I
kept the max_trace_level at 255, so you might get a faster render by
lowering this. You will have to experiment if it will start to introduce
black areas again.

-- sooperFoX

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Attachments:
Download 'cone-photons-trans-down.jpg' (26 KB)

Preview of image 'cone-photons-trans-down.jpg'

"sooperFoX" wrote:
> Also I forgot to add that doing this increased the render time significantly
> (still, only about 16 minutes at 960x600, including photon building), but I
> kept the max_trace_level at 255, so you might get a faster render by
> lowering this. You will have to experiment if it will start to introduce
> black areas again.


I should have read the render report. POV-Ray only used 3/255 max level. I
guess you could leave it at the default, or set it to 10 if you wanted to
be extra safe if you plan to add other transparent objects.


It occurred to me later that in this particular case, because the cone is
sitting with its base on the plane and the top is a point, that instead of
translating the cone downwards you could specify the cone to be open. That
would actually remove the base surface of the cone, so it would now be
impossible to have the coincident surface problem that was causing the
speckles.

cone
{
  <0,0,0>, 5.5, <0,11,0>, 0 open  /* added open keyword */
  translate <-8, -1, 17>
  texture
  {
  ... rest of code unchanged
  }
}


I have tested this and it works. The rendered image appears identical, but
you now don't have to nudge the cone downwards.

Hope this helps.

-- sooperFoX

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