![]() ![]() It is the height dimension that is chosen to be discarded, because it is the (relatively) least important one among others. Assumed height can be either the sea level or the altitude of a (normally) altimeter equipped aircraft. z-dimension) measurement is ASSUMED so you get rid of 1 dimensional measurement out of 4 that were originally required. satellites) can be, instead, used to compute a 2D, horizontal fix (in latitude and longitude) when a certain height (e.g. ![]() In practice, placing expensive clocks in GPS receivers is rarely possible/feasible and 3 space vehicles (SVs, i.e. If we are talking about locating things "inside AND outside" of earth, WELL THEN YES, you need at least 1 more satellite to eliminate one of two possible intersection points in the last step. BECAUSE, there is a reason why GPS satellites are at their specific constellation (~their setup in the sky): !more than! 24 GPS satellites, on 6 orbital planes that are ~20,000 kms above you, and 4 satellites on each plane, 60 degrees between these planes, and 55 degrees inclination with respect to equatorial plane, GIVES YOU 5-8 satellites that you can "connect to" from (almost) any place on earth, and 3 SATELLITES TO GIVE A 3D POSITIONAL FIX ON EARTH. (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 If nothing of this helps, we can go further on this check with pins measures etc.This is a high-tech version of triangulation, called Measure voltage on Fuse 12 in passenger compartment fuse box, check quality of connection on mentioned earth point. If you see this drop of voltage in circuit, as I expect, it is worth to investigate further. When you start the engine, alternator will provide higher voltage on car battery, thus higher voltage in circuit for clock, which might be enough for this higher resistance in circuit to provide enough power for clock to work as needed. But since access to that header is not so easy, worth to make easy checks first, like I said, voltage on clock connector in compare to voltage on car battery withouth starting the engine. de-486097/), or within the earth header for this connection. Higher resistance could be because of corroded earth connection (C0556 on here. Substantial difference could be even 0.5V. ![]() If there is substantial difference, that might be culprit of a problem. It is worth to measure what voltage you have on clock connector in compare to voltage you have on car battery. To me this looks like higher resistance on clock circuit preventing correct current and voltage to the clock itself. ![]()
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