However, if we are given the BSDF as input, we can apply it directly to convert the exterior illumination arriving at the window or skylight into an interior luminous intensity distribution, as we describe in the following section.
2, we describe a new DC method that separates the effect of the BSDF, making annual simulations truly practical, even with complex, operable fenestration.
In the following sections, we describe two techniques for incorporating BSDF data in Radiance.
9 was released in 2008, mkillum has supported BSDF descriptions of window and skylights, using XML files exported from Window 6.
Random sampling is no way to integrate the sun, even if we can account for any complex redirection to the interior with a BSDF.
In the latter case, all contributions are fed through the BSDF and resampled to create a luminous intensity distribution in a mkillum-specific polar coordinate system for treating the window as if it were a luminaire.
In the final mkillum stage, as we pass this light through our BSDF and redistribute the output into a luminous intensity table, we subtract source light that passes straight through the BSDF and continues in the same direction.
While the calculation of luminance distributions for CFS characterized with BSDF data is fairly efficient using mkillum, it still takes some time to sample the exterior environment, account for interreflections and so on, then considerably longer to render a final image using the computed secondary light sources.
This vector dot product is quick to evaluate, making the DC precomputation well worth the effort, but the standard approach must be altered substantially to handle BSDF data and operable systems.
BSDF patches that see only sky will get a contribution from a few sky patches, whereas BSDF patches that see other surfaces in the scene will receive an integration of many sky patches.
For a given sky condition, we could quickly compute the outgoing luminance on the window interior from a BSDF matrix.
Identifying the BSDF matrix as T, we can write our combined matrix formula for a single window group thus: