The required number of rays to do that is too large as the natural variation of the RNG is leading to a big distribution of ray intersections across the module even when no obstacle is present. But that's always the case when trading off number of rays for runtime and would in a way lead to more accurate results.Ĭould I insert a first stage that encompasses my entire scene so that the initial position of the rays is determined in that stage and then carried through all other stages? Once you are in the second stage you shouldn't need to make 4 calls tot he RNG right? Since position and direction is determined by the first stage?īTW - the reason we are doing this is because we are trying to get detail intersection data on a large array of PV modules with obstacles that are causing shade. The consequence would probably be longer runtimes. The advantage would mean that you maintain the ray resolution throughout your entire simulation as rays aren't being culled by previous steps (aside from ones that don't intersect anything, etc). That would require keeping track of power per ray though and may make deeper structural changes to Soltrace. An alternative would be to treat transmission as a decrease in ray power and have all rays pass through the element.

I think that if you set it to 50%, for example, then 50% of the rays will be absorbed and 50% will be transmitted and only the later half make the additional calls. Why doesn't giving the optics some very low transmission value work? Wouldn't then all rays make 4 calls to the RNG? I suspect it's because of the way that Soltrace handles transmission. So there may be a few ways to deal with this:Īlways make the same number of calls to the RNG even if some of them are not used in the case of absorption. If you do that, you should see that both give exactly the same ray data. You can check that the RNG is reproducible in each case by selecting the 'Virtual stage' option on the geometry page for both cases. Because of this, the results won't look exactly the same. once for the sun emission, once for the hit on the surface, once for the angle of transmission through the element, and once for the angle of departure from the element.

The second case with transmission requires at least four calls to the RNG per ray. In the situation you described, the RNG is called in the opaque and perfectly absorptive element twice for each ray intersection, as every ray is emitted and then absorbed without fail. To answer the question, the random number generator (RNG) seed value does ensure reproducibility, but only if the sequence in which the RNG is called is exactly the same between cases. I'm adding a new label for this and will leave this issue open for improvement in this area.

Your point about documentation is a good one.

Soltrace ls3