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    Re: Data reduction request
    From: Frank Reed
    Date: 2013 Nov 18, 19:13 -0800

    Richard, you wrote:
    " Karl, as you probably know, presents the St Hilaire method of sun sites to fix one's location. It seems, from the reaction here, that that is not universally acclaimed as a good method."

    Ha ha. :) No... Nothing could be further from the truth. The "intercept method" sometimes called the "St. Hilaire" method is fundamentally very simple: compare your observations with those calculated from a known position nearby. That's standard, modern celestial navigation, and that's all any of us did here. When you actually know your exact position of observation, the 'intercept method' yields nothing more than the errors of your sights.

    Historically, the idea of comparing a simulation of the sky with the real thing was alien and needed a name. But today it's trivial and hardly seems worth a name. That's all we do in the intercept method -- simulate thee sky and compare with what we actually see. The calculations, however they are performed, provide a simulation of the altitudes of celestial bodies from some known position. When calculation was expensive a century ago, that simulation might consist of only a single calculated altitude and azimuth. Today it's trivial to simulate (calculate) the positions of every star in the sky, and do it based on geocentric data as in traditional celestial navigation, or go straight for the uncorrected (refracted) altitudes that an observer would directly observe. And then as long as the spot for which we are simulating is not too distant from our actual location, the differences we see between our actual observations and the numbers given in the simulation will tell us how far we are from the simulation's chosen "assumed position". And of course, minutes of arc difference equals nautical miles of position offset. Of course, the differences will also include some amount of error in the observations, too.

    A little general advice: don't try to do everything at once. I've seen this happen many times before! :) If you work on your observational technique, and you work on adjusting your instrument, while at the same time trying to create your own analysis tools and develop your own software, you're bound to get frustrated. You won't be able to determine the cause of any discrepancies because you have too many variables in play.

    -FER


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