1,360
edits
Atmospheric light scattering: Difference between revisions
Jump to navigation
Jump to search
→Basic atmosphere model elements
| Line 39: | Line 39: | ||
* The skydome simulates the scattering in an optically thin atmosphere in the absence of haze layers. As such, it takes into account Rayleigh and Mie scattering with the parameters adjusted to account for the water vapour and dust distribution above the current aircraft altitude. The current skydome shader is based on [http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html work by Sean O'Neil] and is described there (in case you're interested in O'Neil's article - the reason why he is able to do what he describes in <i> Eliminating One Dimension</i> is that for realistic rendering distances one can neglect the full curvature of earth and Taylor-expand the expressions in the curvature, his result can then be derived analytically). Extra diffuse high-altitude layers can just be 'painted' onto the skydome. | * The skydome simulates the scattering in an optically thin atmosphere in the absence of haze layers. As such, it takes into account Rayleigh and Mie scattering with the parameters adjusted to account for the water vapour and dust distribution above the current aircraft altitude. The current skydome shader is based on [http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html work by Sean O'Neil] and is described there (in case you're interested in O'Neil's article - the reason why he is able to do what he describes in <i> Eliminating One Dimension</i> is that for realistic rendering distances one can neglect the full curvature of earth and Taylor-expand the expressions in the curvature, his result can then be derived analytically). Extra diffuse high-altitude layers can just be 'painted' onto the skydome. | ||
* A ground haze layer of given thickness and ground visibility takes care of simulating ground fog banks and visibility in the lowest convection layer. This needs to enter the computations of both the skydome and the terrain shaders. | * A ground haze layer of given thickness and ground visibility takes care of simulating ground fog banks and visibility in the lowest convection layer. This simulates diffuse scattering only needs to enter the computations of both the skydome and the terrain shaders. | ||
* An aloft layer simulates diffuse scattering above the ground haze layer. Since the visual impression for anything but large distances is dominated by the ground haze layer, the aloft layer visibility can be modelled as a function of aircraft altitude without creating an unrealistic impression. The aloft layer never obscures the skydome, as its visibility range is supposed to account for the atmosphere looking down, but never looking up where the visibility is much better. | * An aloft layer simulates diffuse scattering above the ground haze layer, also simulating only diffuse scattering. Since the visual impression for anything but large distances is dominated by the ground haze layer, the aloft layer visibility can be modelled as a function of aircraft altitude without creating an unrealistic impression. The aloft layer never obscures the skydome, as its visibility range is supposed to account for the atmosphere looking down, but never looking up where the visibility is much better. | ||
* The really optically thick clouds are drawn by the weather system as separate models into the scene. | * The really optically thick clouds are drawn by the weather system as separate models into the scene. | ||