It would probably be a strange question for here but i will shoot it.

I want to modify the shaders for Prepar3d the next version of MS flight simulator game.

I have ways of interfering with ambient/diffuse ratios on objects terrain e.t.c Also you can control saturation of clouds sky terrain and objects. You can also use expressions and affect the above based on altitude,season,cloud coverage e.t.c

What i am searching for is real life rules that i should apply to the above.


Should i reduce saturation when the weather is full of clouds and light is not enough? What happens to the sky color as the altitude rises?

I know that the rules are infinite but i would appreciate some starting points that will help me adjust:

  • Terrain lighting and saturation based on season and cloud coverage
  • Object reflection lighting and saturation based on season cloud coverage and altitude
  • Water lighting reflection and saturation based on cloud coverage.

I know that all the above depend on which part of the world you are in and many other factors. , so i need just an average for all in order to try to adjust the settings of the simulator close to a real world appearence.


1 Answer 1


I suspect that the answers you seek lie as much in computer graphics and human perception as they do in physics or earth science - for example, colours on a cloudy day won't actually be significantly less saturated than on a sunny one - it's still white light to most intents and purposes - but we may perceive them that way due to the differences in contrast, illuminance, and colour.

There are three components to natural light :

You can calculate the angle of the sun according to time of year, time of day, and latitude. From this angle, and the altitude of your viewpoint, you can estimate the colour of the direct sunlight. The more air it has to travel through, the lower the colour temperature and the intensity.

Then you need to consider the blue sky. This will be lighter at low altitude and darker at high. You'll need to do something about the sunwards sky not being blue at low sun angles. The blue sky casts light on things, but this is mostly only evident by shadows appearing a bit bluer than their surrounds.

Then you need to consider cloud cover. For a flight sim this is complicated by the fact that it may be above or below the camera, or you might be in it. One approach might be to treat clouds as large diffusers that act on the light from the sun and from the blue sky. Whether this is feasible is beyond my ken, and definitely lies in the realm of computer graphics, not earth science.


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