Folks:

I'm having some odd scaling issues with Photons, and would appreciate any
help possible.

I'm attempting to model a LARGE scene with human sized elements in it during
close ups.  To make things easier with existing models I have, I'm using 1
unit = 1 meter.

I have some objects that are Kilometers long.  POV ray seems to handle this
fine, but when I use photons it's doing some weird things.

Specifically, if I model a mirror reflecting a parallel light source into an
object, if the object is small, the scene looks fine.

If I mode the *exact* same object with larger units, at first the object
that the light is reflecting onto doesn't get any light, but an infinite
plan right behind it does.  (rather odd looking).  Scaling the scene
further, the the light on the plane disappears also.

I've tried experimenting with the number of photons and the photon radius,
which helps a little, but when I hit units in the thousands everything
disappears.

Here are a few images.  The scene is simple:

A parallel light at some LARGE distance away (40000 to be exact).

A mirror, rotated slightly to reflect the parallel light
a 'trough' from CSG (two cylinders and a box on top to cut off the trough)
a sphere
a plane.  The texture on the plane is NOT scaled - evserything else in the
scene is scaled by a common scalefactor to show the issue.  You can thus see
the different scales by the plane checker texture.

(this does NOT count as my reflective sphere on a checkered plane! 8-D)

You can see by the light on the edge of the sphere that the light is
'working' and what direction it's coming from.

For the first scenes here, I'm using 200,000 photons - if I increase the
number of photons it does seem to help, but all I'm doing is changing some
'numbers' - the scene itself never changes.  If this is the solution, then
you could simply start using cubes of size .00000001 and have 1 photon <G>.

PhotonScale1000 is with 200,000 photons, PhotonScale1000-2m is with 2
million.

I need to get to 10,000 in scale, but that sort of means I"d be up to
20,000,000 photons, which seems absurd, as the smaller scene generates
essentially the exact same image.

If you compare PhotonScale100, it is essentially identical to
PhotonScale1000-2m, but considerably faster.

Why would the scaling make this much difference?

Should I rescale all my models or is there some global setting I can change?

My settings are simple, for PhotonScale1000-2m I used the below,all others
was count 20000

global_settings {
  adc_bailout 0.003922
  ambient_light <1.0,1.0,1.0>
  assumed_gamma 1.9
  hf_gray_16 off
  irid_wavelength <0.247059,0.176471,0.137255>
  max_intersections 64
  max_trace_level 10
  number_of_waves 10
  noise_generator 2
  charset ascii
     photons {
     count 2000000
     jitter .4
     radius scalefactor

   }

}

#declare CSG001 = union {
  box { // SolarMirror1
    <-1, -1, -1>, <1, 1, 1>
    material {
      Mirror
    }
    photons {
      target 1.0
      reflection on
      collect off
    }
    scale <0.1, 1.5, 1.0>
    rotate 30.0*z
    translate  <-1.2, 1.5, -0.09>
  }
  rotate 55.0*x
}

Post a reply to this message

Attachments:
Download 'PhotonScale1000.jpg' (55 KB) Download 'PhotonScale100.jpg' (63 KB) Download 'PhotonScale150.jpg' (65 KB) Download 'PhotonScale400.jpg' (62 KB) Download 'PhotonScale500.jpg' (59 KB) Download 'PhotonScale1000-2m.jpg' (66 KB)

Preview of image 'PhotonScale1000.jpg'

Preview of image 'PhotonScale100.jpg'

Preview of image 'PhotonScale150.jpg'

Preview of image 'PhotonScale400.jpg'

Preview of image 'PhotonScale500.jpg'

Preview of image 'PhotonScale1000-2m.jpg'