Generates physically based sky environment maps and radiance
samples using the spectral Hosek-Wilkie and Prague atmosphere models.
Functions write high-dynamic-range 'OpenEXR' domes in latitude-longitude
projections, compute per-direction RGB or 55-channel values, and optionally
composite time-accurate star fields and moon phases. Features include
automatic sun and moon positioning from date, time and location, support for
sea-level and high-altitude observers, wide-spectrum coefficients, and
multithreaded C++ acceleration for fast, high-resolution output. For model
details, see Hosek and Wilkie (2012)