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The main one, which is also the stock version required for all tracks, it's the Global Irradiance probe. This is a main probe, that must be placed in a representative area of the track.
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| In general all probes should be placed around 2m above the ground in order to ensure that they provide a representative reflection of the surrounding environment. Placing too high or too low will result in too much or too little sky reflections, and effect the colour of shadows. |
The second option is to use 3D Volumes (Convex Hulls), which are the best option for occluded areas of the track, like garages, tunnels, or roads in between high buildings... and any similar situation where we need to sample the light from the inside of a volume. In the case of a pitlane with garages, that Hull would be nothing more than an easy volume mesh, covering that area, and with a probe inside it, placed in the best position to sample the surrounding.
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You can place this at the top of the scene file, just before any other instance, or where you usually keep the "feature" instanced, like the NoRainZone, Skyboxi, etc... That is not mandatory, you can place it where you want in the scene file, just try to keep it in a place where you can easily check and verify its presence;
Repeat this operation for any Hull you want in the track. For a tunnel is pretty much the same thing; create a volume that can contain the entire tunnel, and place its probe just inside the tunnel, in between the road ground and the tunnel ceiling. Give the Irradiance range a distance that does interpolate properly with the "inside" (Hull) and "outside" area (Global_Probe). If the Hull is pretty much matching the tunnel mesh, you can use a very short range, like couple of meters, so you get a cool transition between the light inside the tunnel and the light outside it.
You can also use micro Hulls to sample the ambient in a place with many trees surrounding the track, so that you want some "greenish" dominant hitting the area. To do so you can just create a very small hull (30cmx30cm box), and place it just above the centerline of the tarmac, in that area. Just use that Hull coordinates for the Probe Position, and use a range that does start from that micro Hull to to the area where you don't have these trees around, anymore. This trick will interpolate the Global_Probe to this Hull in between the high trees, giving that area a grinish and darker shader. Yes, this is more or less imitating a Global Illumination.
Typical mistakes to avoid
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