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8361Re: [aprsisce] Re: Dead Reckoning (was: Instantaneous Course/Speed Vector)

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  • James Ewen
    Apr 1, 2011
      On Fri, Apr 1, 2011 at 10:35 AM, apenadragon <kc2ant@...> wrote:

      >> So, I just need to fix ME's DR to use the last beaconed speed/heading
      >> rather than the current GPS speed/heading and all will be well.
      > Do you?? personally I don't see the issue... the DR is a projection of where
      > the station "should" be...

      Actually Adam, it sounds like you're missing the issue.

      If you take the last reported speed and heading and project that from
      the last reported location, as time progresses, the dead reckoned icon
      will move to where the station "could" be.

      The problem with what we are seeing is that Lynn is using the CURRENT
      speed and heading, and projecting a possible location using that
      information from the last reported location.

      Lets suggest that a position was reported, with a speed of 60 mph, and
      a heading of 90 degrees. After one minute, the dead
      reckoned position should be 1 mile east of the reported location.

      The way it is implemented, if I stop driving east after 30 seconds,
      the DR position would return back to the last reported location. If I
      were to turn south and drive for 1 minute at 60 mph (without sending
      an updated position report), there would be a DR object 1 mile south
      of the originally reported position.

      Now, if this instantaneous line were to originate from the current
      location, it would still be wrong. The line leaving my current
      location would not be a dead reckoned position, but rather a projected
      location for a future position report based on the current speed and
      course, projected into the future the amount of time since the last
      reported position.

      When Lynn gets it straightened out, you'll see something interesting
      happening. As Lynn said, if you continue in a straight line at a
      constant speed, you won't see the projected icon. If the road turns,
      or you change speed, then you'll see the projected (DR) icon continue
      along the last reported vector. Once the Genius settings determine
      that you've strayed too far, a new position report will be sent, and
      the DR icon will start moving away from the reported position again.

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