@himmelszelt/rundbild

rundbild: German, "round picture". A picture of round form, and the wide view from a summit: a panorama, seen from its centre. 19th century, the age of the panorama rotunda.

Environment maps in any projection, as sky and as light.

by Daniel Limberger · Last updated 2 October 2026 · Unfamiliar term?Unfamiliar term Like this one: a dotted underline marks a term this site explains. Hover it, or tap it on a touch screen, and its definition opens right where you are reading. The small numbered citations work the same way, with the source they point to.

Not every sky has to be computed. A photographed or pre-rendered one arrives as an image, and this library is about turning such an image into something a renderer can sample and light with: cube maps, spherical, paraboloid, and polar projections, converted between each other, in HDR where the source has the range for it. From the same image it derives what image-based lighting needs, the diffuse irradiance and the pre-filtered specular levels, so a scene lit by the sky and a scene showing the sky agree with each other.

It also carries the horizon band from the original thesis. Several projections cover only the upper hemisphere and end in a hard edge at the horizon, which a band of ground colour, faded into the lowest rows of the map, hides. The computed skies of dunstkreis and sternenheer can be baked into the same maps, so a renderer can trade a live sky for a captured one without changing anything else.

This chapter is a placeholder: the library does not exist yet. The original’s texture mapped skies are shown in this video.

Projections

How a whole sky fits into a flat image, and back. Not written yet.

Image-based lighting

How the same image lights a scene. Not written yet.

Code examples

Not written yet.