Getting nowhere veeery slooowly.

Now rendering line 26 0f 240 (311373 radiosity samples). 271PPH:  4.5167
pixels per minute on an Athlon 3200+ and dropping as it hits more objects in
the centre of the image.  This is only a preliminary 320x240 render to get
some radiosity samples to reuse for a high definition image later.  I was
going to do the final at 1600x1200 AA 0.3.  Aagh, it'll NEVER finish!

Well, that taught me that function-pigment isosurfaces and radiosity don't
mix  :-)   It's not even near to tracing the isosurface yet, this slowness
is all due to radiosity rays bouncing off other objects (a simplish
mesh-and-cone tree of around 930 finites, not all of it in the scene either)
and hitting the isosurface.

#declare FpPlane = function {pigment {pPlane}}

  isosurface
  { function { y + FpPlane(x,y,z).gray}
    threshold 0.5
    max_gradient 150
    contained_by {box {<-500,-1,-500>, <500,1,500>}}
    texture {tPlane}
  }

Perhaps I could set the max_gradient much lower than 150 and put up with
holes versus the extra speed.  But Povray has already reported a max
gradient of 897 in the isosurface!

Perhaps I could make the isosurface much smaller in the contained_by bounds,
so there's less area for radiosity rays to hit, and use a simple plane of
the same texture pattern ( pigment {pPlane}) for the outer distances.  But
it was intended to be visible over a long-distance shot, and I think that
the boundary is going to be highly visible as a simple plane returns light
very differently (and I'd have to interrupt this render to test it).

Perhaps I should set an accuracy value larger than the default (0.001).  Any
suggestions?  It doesn't have to be a mathematically correct surface, it's
only supposed to represent a rocky ground plane for the artistic statement.

Do you know of a way to "soften" a pigment function as used in an
isosurface, that may reduce that gradient?  This one has a turbulent
function like an agate in it.

I'm also using settings somewhat based on Tim's two-pass radiosity
experiments at NoLights.

    #if (Rad_Pretrace)  // For a low-res high quality first pass
      pretrace_start 1
      pretrace_end   1
      count          300
      nearest_count   10
      error_bound    0.1
      recursion_limit  2
      low_error_factor 1
      gray_threshold 0.2
      minimum_reuse  0.005
      // normal on
      // media on
      save_file "RTCliche4HoH1.rmap"
      load_file "RTCliche4HoH1.rmap"
      // always_sample  off
    #else
<rad settings for the hi-res trace here>
    #end

I haven't actually gone as stringent as some of Tim's settings, but this
scene is still slooow at 320x240.  It looks like I'll have to pull back on
most of those settings.  Which will give the greatest return -- 
recursion_limit and minimum_reuse perhaps?

Without radiosity, the shadows are horribly flat on the very busy surfaces
in the scene.

Should I let this small render run for the rest of the fortnight, so I keep
the radiosity file, then loosen everything up for the final?  How DO you
speed up isos so they complete before your computer dies of old age?

Cheers,
    Brian

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