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Paul

You stated, "My receiver says 132 T and 2232 miles."  As I noted a few weeks
ago I was surprised to learn my Garmin 76 large digital pocket watch gave
not only great-circle distance, but continually updated great-circle course
between two points as well.

I tried your suggestion and received the same course, and distance within 3
nm. My confusion is that 132d is the starting course of a great-circle
route.  I am having trouble understanding why that would be my azimuth.
(spherical trig is still a plug-and-chug function for me).

Bill



> There are other ways a GPS receiver can assist with traditional
> navigation. For example, let's try a sight reduction. I've mentioned
> that possibility on the list before, but didn't explain how to do it
> in detail. So here goes.
>
> Dead reckoning position is 25 51 N 069 25 W on 2005 Mar 17 1500Z. Load
> that position into the receiver as waypoint DR1.
>
> At that position we do a sextant sun shot. Ho = 52 39.
>
> Almanac says Sun GHA = 42 55.6, dec = S 1 08.7. Load the Sun's
> geographical position as waypoint GP1, using GHA as the west
> longitude. (If GHA is greater than 180 the receiver will probably
> reject it as a west longitude. In that case, convert to the equivalent
> east longitude.)
>
> Now use the receiver's route function to find the bearing and distance
> from DR1 to GP1. My receiver says 132 T and 2232 miles. Convert the
> latter to degrees and minutes (60 miles = 1 degree): 37 12. Hc is 90
> degrees minus that angle, or 52 48.
>
> The USNO online sight reduction calc says Zn = 132.5, Hc = 52 48.3.
> Close enough!
>
> Ho is 9 minutes less than Hc. If desired, that correction can be
> applied to the DR position without any plotting: use the receiver's
> waypoint projection feature to set a waypoint 9 miles from DR1 in the
> opposite direction from the Sun. I get 25 57.0 N 069 32.4 W. Save that
> as the estimated position.

   

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