sky-view

Recipe for computing Sky View (aka. Sky Component).

Sky View is defined as the percent of the sky dome seen by a surface. This can be computed either using a uniform (default) sky or a cloudy sky. Note that sky view's definition means that sky regions directly in front of the surface carry more weight than those at the sides.

Note that computing cloudy Sky View for a vertically-oriented geometry (horizontal sensor direction) will yield Vertical Sky Component (VSC) as described by the UK Building Research Establishment (BRE). VSC is defined as the ratio of cloudy sky illuminance falling on a vertical wall to the simultaneous horizontal illuminance under an unobstructed sky [Littlefair, 1991].

Also note that this recipe still respects the transparency of objects, reducing the percentage of the sky visible through a certain geometry by the transmittance of that geometry.