Night driving is currently available across all NADS simulators. Most of the NADS tile library files are constructed to function in dual modes: normal daytime and night scenes. There are 3 major time-of-day settings available: daytime, dusk, and night. These are flags enabled within the source tile or model, and the image generator displays each model representation based upon the specified time of day. Most models incorporate all three settings for a realistic representation.

Normal daytime scene - default settings (Click on the image for a larger version)

Night lighting approximation

A night-time condition is achieved through lowering overall ambient illumination in the scene by adding black to each pixel, which darkens the scene. It is possible to approximate the effects of illumination at night through the use of modeling techniques which are standardized in the simulation community. These techniques include the use of self-illuminated polygons, which are in fact special polygons rendered at full intensity and thus are not affected by the night condition. Light pools may be depicted as textured polygons, and vehicle headlamps modeled as self-illuminating polygons with a lens flare texture to enhance the illusion of a light source.

Night scene with texture light lobes, self-illuminating surfaces, reduced ambient illumination (Click on the image for a larger version)
Global illumination scene: dynamic object does not cast a shadow--default appearance for a vehicle with headlights enabled (Click on the image for a larger version)
Simulated light source glow (Click on the image for a larger version)

Headlamp approximation

The NADS image generators do not currently support real-time ray tracing or light sources. Therefore, it is not presently possible to implement scenes that contain emissive light sources illuminating objects or entities within the scene. An approximation of ownship headlamps is achieved through the use of a light lobe map that “illuminates” the region near the ownship. This is accomplished by rendering pixels within the light lobe coverage at a specified intensity, unaffected by time of day settings, with reasonable falloff.

Headlamps on ownship using light lobes at dusk (Click on the image for a larger version)

Ownship lobe settings which may be modified through the ISAT include:

Reduced visibility

Reduced visibility is achieved through adding a groundfog color to the scene and setting a maximum visibility threshold. Color is added to surface pixels based upon their distance from the viewer, with closer pixels receiving less coloration and further pixels receiving more.

Default visibility (Click on the image for a larger version)
Reduced visibility (Click on the image for a larger version)
Reduced visibility, dusk (Click on the image for a larger version)