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    GPS trick: compass rose waypoint
    From: Frank Reed
    Date: 2010 Feb 1, 19:04 -0800

    I mentioned this to trick to Greg Rudzinski and Gary LaPook while I was in California. They said I should bring it up on NavList.

    If you're doing ordinary small boat sailing on a local chart, enter the coordinates of the center of the compass rose on the chart as a waypoint in your backup handheld GPS unit. Then you can ask it for bearing and distance from that waypoint at any time. This makes the plotting very simple since you can plot out from the center on the reverse bearing from the compass rose. If the GPS says the center of the compass rose bears 60 degrees true at 5.25 n.m. distance then you place your straightedge on the chart along 240 degrees true (=60+180) and measure off 5.25 miles from the center of the compass rose.

    This is a nice, simple trick that I had understood to be "common knowledge". I don't recall when I first heard it, but it was at least ten years ago. Whether it's easier or less error-prone than just plotting latitude and longitude will depend on the user. Naturally the accuracy of a "polar plot" like this from a fixed waypoint decreases as distance increases. As always, common sense is still required.


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