Re: How GPS works

Sorcerer wrote:
http://www.androcles01.pwp.blueyonder.co.uk/GPS.htm

It's wrong at a very fundamental level -- it requires a minimum of FOUR GPS satellites to determine one's position AND TIME. The GPS receivers have no clock (or at least no clock that is usefully accurate).

Also the velocity of the satellite in the direction of the receiver is not "negligible".

And an offset in time of all satellites would destroy differential GPS, which is used in the most critical applications (e.g. busy harbors).

And the website omits several other important corrections, among the most prominent is the Sagnac effect.


Tom Roberts
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Relevant Pages

  • Re: to sam
    ... A GPS receiver determines its position ... with respect to several GPS satellites by a process call trilateration. ... Clock(B) notes that it is time+ I1 on its' clock. ...
    (sci.physics)
  • Re: to sam
    ... A GPS receiver determines its position ... with respect to several GPS satellites by a process call trilateration. ... Clock(B) notes that it is time+ I1 on its' clock. ...
    (sci.physics)
  • Hijacking Satellite Navigation Sending false signals to GPS receivers could disrupt critical infrast
    ... Sending false signals to GPS receivers could disrupt critical ... The Global Positioning System (GPS) lies at the heart of an increasing ... roughly 30 satellites orbit the earth, ...
    (sci.military.naval)
  • Re: GPS ques
    ... >> GPS is massively corrected. ... > 2) Three satellites put you on the line of intersection of two ... There is no ambiguity, since it's all done with mirrors. ... it's doesn't have to be a clock, ...
    (sci.physics)
  • Re: Beidou (or .. how to do sat. nav. with just 3 sats)
    ... > It is a direct ranging system. ... > unknowns (3D posn and clock offset), and you need four observations to ... Hence GPS requires four SVs. ... Most expanations begin by considering three satellites, ...
    (sci.geo.satellite-nav)