Photon Setup for Outdoor Scenes

Photon Mapping can be very effective in replacing a skylight rig with a sun. This is not the only use of Photon Mapping for outdoor scene but it is the most basic setup which you will want to improve in different ways,

The basic scene setup is simple: place an object on a floor and cover it with a skydome making sure the floor closes the skydome. Then place a bulb light near the dome, turn ON radiosity and render with Photon Mapping.

This is the basic idea. But in order to get a nice indirect illumination, here again, the radiosity attributes need some special attention. The first issue to consider is the small size of the object of interest relative to the size of the whole scene. Because of this, the object itself will receive a small number of photons relative to the rest of the scene. Of course, it would be possible to compensate with a tighter dome but this would place the light too close to the object. The other option is to shoot a large quantity of photons in the scene. Shooting 1M photons is not unreasonable for such a scene.

The second issue to consider is the number of photon bounces. In this case, a large number of bounces would pollute the sky with photons coming from the ground, the main object and the other objects in the scene thus producing an indirect illumination from the sky wich is no more bluish. This is clearly not what we want