Le 18-04-16 à 19:16, muyu a écrit :
> I am simulating outdoor scene using radiosity. Regarding the light source, I
> used one parallel light to simulate the beam. However, how could I simulate the
> hemispherical diffuse radiation? Thanks in advance.
> 
> Shouyang
> 
> 

Basic way :
Simply use a sky_sphere and radiosity.

The sky_sphere will take the role of the blue sky and cast a bluish tint 
on your scene.
sky_sphere{
	pigment{
		planar colour_map{[0 rgb<0.01, 0.1, 0.9>][1 rgb 0.7]}
		}
	}

Make your «Sun» slightly yellow to compensate.

Use radiosity. It will enable the sky_sphere to actually emit some light 
onto your scene.
You can use radiosity with the default parameters like this :
global_settings{ radiosity{}}

The defaults can be good enough for a scene using a regular light 
source, such as your Sun.

If you want some clouds, you can use a plane or a large flattened sphere 
with some cloud-like pattern. Make that object hollow to allow you to 
use any media of fog, it also will suppress a warning about the camera 
been inside a non-hollow object. In several cases, it's good enough, 
especially if you don't see the sky directly.

More advanced, and much longer to render :

Keep a black background.
Surround your whole scene with some huge object, like a plane or very 
large box, sphere or cylinder with the hollow option.
Fill that object with scattering media using the Raleigh model. Make 
that somewhat blue.
This will scatter the blue around and make your «Sun» appear yellow.
Take a look at the sample scene mediasky.pov for an example of that.
Optionally, add some media based clouds.
Here also, radiosity can help. You need to, at least, add media on in 
the radiosity block :
radiosity{media on}

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