"Bald Eagle" <cre### [at] netscapenet> wrote:
> "muyu" <lsy### [at] gmailcom> wrote:
> > 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
>
> Create a hemisphere (perhaps with an opaque flat back) and assign a light source
> to it.
>
> From the [F1] documentation
>
> 3.4.3.1.7 Looks Like
>
> By default a light source has no visible shape. The light simply radiates from
> an invisible point or area, however there are cases where this is not desired.
> Using looks_like is as an easy way to override this behavior. There is an
> implied no_shadow so that light is not blocked by the object, without it the
> light inside a non-transparent object could not escape. The object would, in
> effect, cast a shadow over everything.
>
> When using looks_like there are a few important things to consider:
> 1.the object should be positioned at the origin
> 2.it's generally easier but not necessary to declare the object beforehand
> 3.works with point and spot lights not parallel lights
> 4.use a union instead if you want the object to block light and remember to make
> some portion of the object transparent
>
> See the following examples:
> #declare My_Lamp_Shape = sphere { <0, 0, 0>, Some_Radius }
>
> // using looks_like
> light_source {
>   <100, 200, -300> color White
>   looks_like { My_Lamp_Shape }
>   }
>
> // using union
> union {
>   light_source { <100, 200, -300> color White }
>   object { My_Lamp_Shape translate <100, 200, -300> }
>   }

I think I did not explain myslef clearly. I would like to simulate diffuse sky
radiation, which distribute isotropically over the hemisphere. Thanks in
advance.

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