The illumination and appearance of the solar/skydome is critical for many applications in computer graphics, computer vision, and daylighting studies. Unfortunately, physically accurate measurements of this rapidly changing illumination source are difficult to achieve, but necessary for the development of accurate physically-based sky illumination models and comparison studies of existing simulation models.

To obtain baseline data of this time-dependent anisotropic light source, we design a novel acquisition setup to simultaneously measure the comprehensive illumination properties. Our hardware design simultaneously acquires its spectral, spatial, and temporal information of the skydome. To achieve this goal, we use a custom built spectral radiance measurement scanner to measure the directional spectral radiance, a pyranometer to measure the irradiance of the entire hemisphere, and a camera to capture high-dynamic range imagery of the sky. The combination of these computer-controlled measurement devices provides a fast way to acquire accurate physical measurements of the solar/skydome. We use the results of our measurements to evaluate many of the strengths and weaknesses of several sun-sky simulation models. We also provide a measurement dataset of sky illumination data for various clear sky conditions and an interactive visualization tool for model comparison analysis available online.

Joseph T. Kider Jr., Daniel T. Knowlton, Jeremy Newlin, Yining Karl Li, and Donald P. Greenberg. A Framework for the Experimental Comparison of Solar and Skydome Illumination. ACM Transactions on Graphics (Proceedings of ACM SIGGRAPH Asia 2014). 33(6), Article 180, November 2014.

@article{Kider2014FEC,
    author = {Kider,Jr., Joseph T. and Knowlton, Daniel and Newlin, Jeremy and Li, Yining Karl and Greenberg, Donald P.},
    title = {A Framework for the Experimental Comparison of Solar and Skydome Illumination},
    journal = {ACM Transactions on Graphics (Proceedings of ACM SIGGRAPH Asia 2014)},
    volume = {33},
    number = {6},
    month = nov,
    year = {2014},
    articleno = {180},
    doi = {10.1145/2661229.2661259},
    keywords = {measurements, skylight models, spectral, validation},
}

This work was supported by Autodesk for energy and daylighting simulation research, along with funding from NVIDIA and Pixar Animation Studios. Wenzel Jakob's Mitsuba Renderer was used for all renderings. The auhors are grateful to Bruce Walter, Kavita Bala, Steve Marshner, William Philpot, and Adam Arbree who always were willing to provide feedback and guidance. We especially wish to thank Kevin Pratt, Lars Schumann, and Hurf Sheldon who assisted in building the device.

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