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    Re: A practice round of stars
    From: Peter Hakel
    Date: 2013 Mar 2, 00:14 -0800

    Hello Jeremy,

    Thank you for another excellent round of sights.

    The computed fix at 19:00:00 local time is:

    Lat: N 8d 49.0'
    Lon: E 109d 45.2'

    This position is marked by dark squares on the two linked plots. The LOP's in the first plot (VSOP sheet, 20 nm per inch) do not account for the motion of the vessel. In the second plot (on metric graph paper using Kermit's favorite scale of 1 nm per centimeter) the AP has been individually moved by DR for each body before the LOP's were plotted.

    The plots show the value of having as many bodies as possible for a confident fix. They also show the danger of having only two bodies whose azimuth difference is close to 0 or 180 degrees.

    Accounting for the motion of the vessel is also important, especially for pairs of nearly parallel LOP's. On the metric plot the Jupiter-Moon and Fomalhaut-Capella pairs still intersect a bit far off from the dark square, but not nearly as far as they place on the VSOP plot.

    The metric plot with its "zoomed-in" scale reveals that all LOP's run within a mile of the computed position, which I think is awesome. :-) Do you have the GPS position to compare with?


    Peter Hakel

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    File: 122574.sights.xlsx
    File: 122574.many_body_fix.xls
       
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