BRTF measurements & some thoughts

Hi all,

since the Radiance 2010 workshop CD, in which it was planned to be added, seems still in the making, and in light of Andy McNeil's nicely done and informative three-phase tutorial, it might be worthwhile to mention that the workshop talk on bidirectional-reflection-transmission-data (BRTF, BSDF, BTDF, etc) basics, measurement and modelling had already been put at http://www.pab-opto.de/radiance/pab-brtf-talk.web.pdf . It gives some compact summary from solid angle to BRTF, some basics on measurements and some thoughts based on previous experience with Radiance BRTF models.

For those who are primarily concerned about how to get measured BRTF into Radiance at all, LBL's newly introduced, matrix based approach is certainly a big step forward, that is vital to handle measured BRTF + Radiance in a general, project oriented, way.

For folks who endeavour to explore the BRTF world closer, and without going into too much detail here, there still seems good reason to consider a matrix based approach as not quite optimal for many of the most interesting materials. For the entertainment of the curious, reasons are given in the last 10 pages or so of the talk. Funny bit to mention: Both views are based on the same data generating measurement gonio-photometer (http://www.brtf.info/?d=/gonio-photometer).
Whether or not this will influence any further and/or additional ways of getting BRTF data into the Radiance simulation program in an adaptive and sleek way, with less steps on the user-side, is to be seen. Technically, there are one or two fairly major programming tweaks to this, and both are inside the current rendering core code.

happy rendering,
feedback appreciated

Peter

PS: cross-posted to radiance-dev, in case of further technical threads

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since the Radiance 2010 workshop CD, in which it was planned to be
added, seems still in the making, and in light of Andy McNeil's nicely
done and informative three-phase tutorial, it might be worthwhile to
mention that the workshop talk on
bidirectional-reflection-transmission-data (BRTF, BSDF, BTDF, etc)
basics, measurement and modelling had already been put at
http://www.pab-opto.de/radiance/pab-brtf-talk.web.pdf . It gives some
compact summary from solid angle to BRTF, some basics on measurements
and some thoughts based on previous experience with Radiance BRTF models.

Hi Peter, hi list...

First - thank you for putting your presentation online! I felt it was certainly one of the great moments of the workshop. Radiance (or lets say Greg) has done a lot of progress in supporting certain applications by adding the matrix-based toolchain. Still, fast progress usually needs a critical review. And that is where you stepped in on the workshop - it is really important that people know what it means to reduce angular resolution, where it is useful and where it has to fail. As well as to understand the limitations of other approaches, such as functional descriptions, in Radiance's current implementation. I somehow feel that such a discussion on the limitations and implications of the approach may be even a valueable addition to the (great!) tutorial Andy wrote for us.

Cheers, Lars.