The first uses latitude-longitude panoramic format, also known as an equirectangular mapping. This is the same format that I use for HDR environment maps in Photorealizer, and my sky renderer already saves images to EXR (in addition to PNG), so I will be able to use my sky renderer renders as HDR environment maps for my Photorealizer renders. Plus, I have HDR environment map importance sampling in Photorealizer, so I can leave the tiny, bright, influential sun in the sky images and Photorealizer will automatically know to heavily sample the sun.
The second new camera uses an angular fisheye projection. This is a pretty intuitive way to view the entire sky (and part of the ground in my implementation). This kind of picture can be captured in real life in a single shot with a fisheye lens. Real fisheye lenses are pretty advanced. Here is a site that shows how a real fisheye lens works, with nice diagrams of the fancy optics.
|Angular fisheye projection.|
The environment is identical in both images above. The solar elevation angle is 10°. I think that the two bright peaks above the horizon in the solar and anti-solar directions are due to the forward and backward peaks of the Rayleigh scattering phase function.