MaxNumTests_ is the upper limit on the number of scene line tests.bTestDownOnly_ culls line tests that are not in the "down" direction.TestRange_ indicates how close to "down" tests need to be; 1 means only vectors pointing straight down are tested, 0.5 would include any vector about 45 degrees from straight down, 0.0 means any vector pointing down at all, and negative values up to -1 would include vectors pointing up.CollisionChannel_ denotes which scene objects to collide against.