The GPS can orientate three-dimensional locations by triangulation. Two-dimensional locations can be
calculated with data from two distinct satellites. However, data from a third satellite is usually included to
correct and revise errors. Similarly, to obtain more precise three-dimensional locations, data from a fourth
satellite in addition to that from the basic three satellites is often included to eliminate and revise possible errors
in positioning. In general, users only need to confirm that their GPS receiver is obtaining data from four or more
satellites; positioning information can thus be calculated more precisely and effectively used in application [9].