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13739RE: [aprsisce] Paths and position ambiguity.

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  • Bob Bruninga
    Nov 7, 2011
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      > ... the "rectangle of ambiguity", or "circle of
      > ambiguity" is actually a line of ambiguity,
      > as per APRS spec.

      Sorry, that is an incorrect interpretation. The degree of ambiguity is
      carried in the Latitude digits, but it applies to both latitude and
      longitude. And it is not simply a "masking" of digits.

      Ambiguity is a function. It has four levels. And it defines the circle of
      ambiguity.

      What confuses people is when they think of it as a simple truncation or
      masking of digits. That may appear to be how some systems implemented it,
      but that is not how it is defined.

      We have got to think back before GPS. If I know my position to 1 mile, I
      write it as 3859N 07629W If I know it to a tenth of a mile, I write it as
      3859.1N 07629.1W and if I know it to 60 feet, I write it as 3859.11N
      07629.11W.

      That is what position ambiguity transmits. Oh, some clients and radios may
      have confused things by transmitting the precise longitude digits while
      putting in the proper ambiguity in the Latitude. That is a kenwood bug, not
      the definition of Ambiguity.

      Hope that helps.

      Bob, Wb4APR
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