• 17 June 2022
  • 1 reply

Dear all,

I not clear about “sampling importance” about scatter to method menu. The size is about the size of radious of the sphere that would be placed in target object but the limit ? why “1” is the default value? 1 stereoradian? 

The difference between power total with or without sampling importance is almost the same. I understood that importante sampling has to do with the scatter effect in the surface. 

thank you in advanced for your comments


Best answer by Berta.Bernad 20 June 2022, 12:36

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Hi Sonia,

Importance Sampling speeds up scattering analysis by always choosing scattered rays that will propagate in a desired direction. To determine the direction for the scattered ray, a target sphere is defined. The target sphere is defined by position, size, and limit. As you said, the size parameter defines the radius in lens units of the target sphere. The limit parameter is used to define the maximum solid angle in Steradians of the target sphere as seen from the scatter point. It is defined to ensure the BSDF of the scattering surface doesn’t vary too much within the solid angle subtended by the target sphere, since if the BSDF changes appreciably over the solid angle of the target sphere, the flux seen at the target sphere from importance sampled rays may not be accurate.

To get an idea of how importance sampling improves scatter efficiency and analysis time you can have a look at the following article: How to use importance sampling to model scattering efficiently – Knowledgebase (