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    Re: Position from altitude and azimuth.
    From: Bill Lionheart
    Date: 2020 May 13, 10:14 +0100

    I would just like to add that in the pdf I posted from Mathematica the
    variable LHA is measured East so is negative LHA.
    Isoazmuth curves are interesting and
    https://en.wikipedia.org/wiki/Isoazimuth gives a formula for such a
    curve. As is common the best thing about Wikipedia is it cites useful
    reliable sources in this case an article in American Mathematics
    Monthly https://www.jstor.org/stable/2304185?seq=1#page_scan_tab_contents
    I was thinking though that an Isoazimuth is a curve joining points P
    where the great circles to two other fixed points Q and R meet at a
    specified angle, but for the special case Q is the north pole.  In
    plane rather than spherical geometry, replacing great circles by
    straight lines,  this is an arc of a circle.
    Another interesting link to follow is the Littrow projection
    https://en.wikipedia.org/wiki/Littrow_projection  . On this map
    isoazimuths to some fixed point are straight lines.  Not useful for
    the single sight fix, but perhaps for position lines for a single high
    frequency radio beacon where the DF bearing is taken from a mobile
    Bill Lionheart
    On Wed, 13 May 2020 at 06:16, Antoine Couëtte  wrote:
    > Dear Peter and Lars,
    > Excellent example from you Peter and excellent explanation from you Lars.
    > -If you follow a great circle from one Departure Point (e.g. 
    Санкт-Петербу́рг) at a given Departure Track Heading and over a given 
    Distance you will eventually hit your arrival point, which is unique.
    > - But this does not imply the existence of only one such unique/single 
    Departure Point with both same Departure Track Heading and Distance to hit 
    this very same unique arrival point !
    > Since we do not have accurate enough azimuth references on board most craft, 
    we are - or maybe better : at least I am - insufficiently familiar with Equal 
    Azimuth Lines.
    > Peter, we have here an excellent example of an Equal Azimuth Line (030° 
    towards one unique arrival point) having 2 different intersections with a 
    circle of equal altitudes centered on that same and unique arrival point.
    > I really learnt something here.
    > Thanks also and again to you Dave for having given us this example to study.
    > Best Regards,
    > Antoine
    > View and reply to this message

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