When I saw 81 points of sky radiance, I said, now that’s interesting, I’m working with exactly 81 points of sky radiance samples myself, measured by my advisor (Joe Kider) on the rooftop of the Frank Rhodes Hall building at Cornell between 2012-2013. I wonder why they chose 81 points exactly, since the sampling pattern is arbitrary?
Then I saw slide 52 of that presentation @sarith posted . And Tohsing’s on the next page.
Kider Jr, J. T., Knowlton, D., Newlin, J., Li, Y. K., & Greenberg, D. P. (2014). A framework for the experimental comparison of solar and skydome illumination. ACM Transactions on Graphics (TOG), 33(6), 180.
Tohsing, K., Schrempf, M., Riechelmann, S., & Seckmeyer, G. (2014). Validation of spectral sky radiance derived from all-sky camera images-a case study. Atmospheric Measurement Techniques 7 (2014), Nr. 7
I’m using this exact spectral data myself, but on a different (non-rendering) project at the moment. Perhaps if I find out more about circadian lighting I could help…