[Radiance-general] BSDF xml into Radiance

[Lars O. Grobe]

Hi Andy, hi list-subscribers,

I just came across this recent message about the usability of the bsdf
material type with patch-based models of the sky including direct sun
and complex fenestration. To avoid misunderstandings, I will try a short
summary for others to comment on available options for annual
simulations with complex glazing:


1) classic radiance tools (rpict, rtrace), complemented by mkillum to
relax ambient setting.

Advantages: low noise, validated.

Disadvantages: very slow for annual simulations, no support when
non-planar specular reflective surfaces are involved.


2) rtcontrib and patch-based model.

Advantages: faster for annual simulations.

Disadvantages: noise, nice images require high (slow) -ad and cannot be
optimized using mkillum, limitations about specular non-planar
reflectors apply.


3) rtcontrib and patch-based model, bsdf.

Advantages: support for non-planar reflectors, should be slightly faster
then 2) as the fenestration system does not have to be traces internally
- did anyone compare?

Disadvantages: still high -ad settings required leading to extended
rendering times and still no way to get mkillum in, tends to
underestimate direct sun (according Andy's message).


4) three-phase-method.

Advantages: very fast, can also be used with non-planar specular
reflectors as bsdf data is supported.

Disadvantages: requires quite a lot of set-up work, e.g. subdivisions to
reflect external obstructions. Patches visible in the results,
fenestration geometry is not visible.


5) pmap.

Advantages: can be used with non-planar reflectors and multi-peak
transmission.

Disadvantages: unknown status (any news?), not integrated with rtcontrib
(contributions would need to be rendered manually).


So if I need a way to generate images with visible fenestration
geometry, the only reliable option would be 2), which requires very
hight settings for -ad and thud will still be rather time-consuming, if
noise is to be controlled.

Cheers, Lars.

On Tue, 2012-06-12 at 08:43 -0700, Andrew McNeil wrote:

> Though I've found that the BSDF material doesn't work well for
> daylight coefficient based annual simulations (I'm assuming dds.bash
> is a dynamic daylight simulation script).  Putting the solar radiance
> into skypatches relies on probabilistic sampling to find patches
> containing the sun, and if you don't have much direct transmission
> from the direction of the sun, you aren't likely to find the sun.  Not
> finding the sun causes big errors.