Can I ask a follow-up question on shadow techniques. Our application is basically for highway/road constructions. So the user is creating all the data (ie difficult for us to predict). If we wanted to draw shadows to the 3D views what technique would you suggest. Speed is important but currently we render to video for drive throughs and could restrict shadows to this option if the render time was to slow. The main thing would be that the user gets good shadows without having to fiddle a lot of parameters
PCF is no silver bullet. Especially with larger kernels, you end up with oddball stuff like flat near terrain shadowing far terrain even with the light source above the ground. Crank aniso on the shadow map up to 8-12, and IIRC it gets worse – bigger integration area (that’s for a standard shadow map with no MIPs too).
Sounds like your camera is at or near the ground, potentially with a large depth range toward the horizon.
Would suggest looking at Cascaded Shadow Maps aka Parallel-split Shadow Maps. This gives you finer-spatial res shadows up-close and courser-spatial res shadows further away (like you need with a perspective frustum). Can be applied fairly orthogonally with filtering techniques such as PCF, VSM, etc.