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Re: Position from altitude and azimuth.
From: Bill Lionheart
Date: 2020 May 13, 10:14 +0100
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 station. Bill Lionheart On Wed, 13 May 2020 at 06:16, Antoine Couëttewrote: > > 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 > >