[Radiance-general] Hardware accelerated radiance

[Carsten Bauer]

Michael Kruger wrote:
>
> 
> ps: Another major problem for point + shoot rendering from 3D modeling 
> programs is ensuring oconv has a bounded finishing time for any given 
> model. Most models I work with in AutoCAD or Lightwave (exporter coming 
> Real Soon!) need extensive conversion work before oconv will run to 
> completion. (Most often it simply runs continuously until it dies 
> because it uses up all available memory. >4GB! ) Are other people having 
> similar problems?
> 
Hi Mike,

the oconv code is not much if counted in lines and statements, but it is 
  definitly one of the complicated parts of Radiance. The memory issue 
is certainly connected to the amount of fine detail in the scene, as one 
algrithm within oconv calls itself recursively again and again when 
stepping down the tree and subdividing the cube into octants and 
suboctants etc. This results in oconv 'blowing' itself up considerably, 
using far more memory for the process than the produced octree later has 
itself.

This means by subdividing the scene beforehand and then including the 
parts as instances you have far better chances to get a model 'oconved'.
(If I remember it right Greg once said that by using instances and 
subinstances etc the whole world could be converted to an octree with 
resolution down to some inches ...)

Another optimisation comes into play: if you have lots of similar 
instances, they are only allocated once. A drawback of using instance is 
that every ray has to undergo a transformation on entering, but for huge 
models this effect becomes negligible.

All in all this means of course some appropriate user intervention. 
Coming up with an automatic solution which e.g triggers subdivision of 
the scene automatically presumably will be not easy :-)

-Cb