(The ELIMINATION of the second point, on the bottom left figure of the illustration above, is done "intuitively" as it corresponds to someplace in DEEP SPACE. !YES!, you !could have gotten! a 3D position fix with 3 satellites IF the GPS receiver you are using was equipped with an atomic clock. 3 satellites could be used to determine 3 position dimensions with a 'perfect' receiver clock (with an expensive atomic/optical clock). So, even though 3 spheres we obtain by 3 distance measurements intersect at two different points, one of those points is rendered useless by characteristic of the coordinate system GPS assumes we are interested in locations below the earth's atmosphere. Any location in this 3D space requires no more than 3 components to be completely identified. Global positioning system(s) assume an 'earth centered, earth fixed, x-y-z 3D cartesian coordinate system'. Radio navigation systems trilateration is the basis of GPS. Both of these systems are also commonly used with More sites, or with triangulation, which uses the measurement ofĪbsolute angles. Multilateration should not be confused with trilateration, which usesĭistances or absolute measurements of time-of-flight from three or Even when GPS is leveraging more than 4 satellites, it is still doing trilateration, as opposed to multilateration, which GPS does not use. points out, this is not a form of triangulation. Timing and location correction and selects one of the remaining twoĪs R.K. Finally, the forth satellite helps calculate a The third satellite reduces the choice to two possible To a circle created by the intersection of the two satellite spheres The second satellite narrows your location The first satellite locates you somewhere on a sphere This is a high-tech version of triangulation, called
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