1. A navigation system for use with a mobile unit, the system comprising: range sensors configured to collect range data; a data storage system having stored therein a multidimensional evidence grid comprising voxels having voxel volumes representing probabilities of occupancies of points in space within an environment and a sensor model comprising adjustable parameters representing inaccuracies of the range sensors, wherein probability information for a voxel comprises a plurality of probability values for each point in space determined from the range data; a grid engine configured to adjust the adjustable parameters based on received range data from the range sensors; and a navigation module configured to direct the mobile unit though the environment using the evidence grid, received range data, and adjustable parameters.