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Vehicle Lighting

The Lighting page of a vehicle's Basic properties enables you to define the eclipse central body list used for lighting computations. The default list of eclipsing central bodies consists of the central body of the satellite and its moons.

Select Use Customized List to select available central bodies and then use the blue arrow to move the selected central bodies from the available list to the assigned list.

Clear Use Customized List to restore the original list of default central bodies.

Lighting Model

The lighting model determines the obstruction surface used when computing lighting information (e.g., penumbra, umbra, solar intensity) when an eclipse body is the vehicle's own central body. Choose Central Body Shape to use the vehicle's central body ellipsoid shape as the obstruction surface (this is the same shape that is used for the vehicle line-of-sight access constraint) or choose Terrain to consider the effects of the vehicle's central body terrain on lighting.

Lighting information computed for other eclipse bodies that are not the vehicle's central body use the eclipse body's ellipsoid shape as the obstruction surface. Thus, an Earth satellite would consider Earth terrain if chosen, but Lunar terrain would be ignored (the Moon's central body shape would be used instead). Likewise, a Lunar ground vehicle could consider Moon terrain for lighting if chosen but would ignore Earth terrain.

The computation of sunlight, penumbra and umbra time intervals is performed by sampling the angle between the sun's disk and the eclipse body obstruction surface during the vehicle's ephemeris span. Those samples are processed to find the times when that angle indicates that the disk is partially or fully obstructed.

The maximum stepsize allows you limited control over the sampling. Normally, the default sampling algorithm samples sufficiently to insure accurate results (to within a five (5) ms tolerance). However, because terrain is irregular and not smooth, a smaller stepsize should be taken between samples to achieve accuracy. Setting the maximum stepsize smaller when considering terrain can help the algorithm find short duration events, but the lighting times computation will take longer to compute.

Rarely would it be necessary to adjust the maximum stepsize smaller when using a central body shape as the obstruction surface. It has been provided if that case arises.