computeBestAvailableLevelOverRectangle
Finds the most detailed level that is available everywhere within a given rectangle. More detailed tiles may be available in parts of the rectangle, but not the whole thing. The return value of this function may be safely passed to sampleTerrain for any position within the rectangle. This function usually completes in time logarithmic to the number of rectangles added with TileAvailability.addAvailableTileRange.
Return
The best available level for the entire rectangle.
Parameters
rectangle
The rectangle.