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    Re: Spherical earth model vs. ellipsoid
    From: Henning Umland
    Date: 1999 Mar 15, 2:43 PM

    Date sent:      	Mon, 15 Mar 1999 13:07:11 +0100
    From-           	Jim Manzari 
    Organization:   	am Buck
    To:             	navigation@ronin.com
    Subject:        	Re: [Nml] Spherical earth model vs. ellipsoid
    Send reply to:  	Jim Manzari 
    > Henning,
    > I was intrigued by your test.  It appears to have been well planned
    > and executed.  Thanks for posting a very interesting summary of the
    > results.
    > You've expressed a doubt as to whether the method may be applied
    > elsewhere in the world.  Perhaps my experience in a similar experiment
    > might give you some food for thought.
    When I made my experiments, I was aware that the spirit level can
    be deflected by local anomalies of the earth's surface like ,e.g., ore
    deposits, mountains, lava plugs, etc.
    Fortunately, the area southeast of Hamburg is absolutely flat, the
    ground consists only of clay, sand, and pebbles deposited by
    glaciers, and we don't have ores and other heavy minerals here.
    I was thinking of geometric anomalies in other parts of the world,
    for the earth is not really an ellipsoid but has a rather irregular
    shape with local depressions and the like. I once saw an image
    showing the exaggerated irregularities of the earth. It looked like a
    dented apple.
    The theodolite I have is a TOPCON DT-102. It is an electronic
    model with a built-in microprocessor and digital display. Further, it
    has an electronic tilt compensator which is a very useful device
    since the legs of the tripod sometimes change their length to a
    different degree when irradiated by the sun (otherwise you would
    have to adjust the spirit level repeatedly).
    Although mostly used for surveying, theodolites are valuable
    instruments for celestial navigation as well (on land only!). Due to
    their superior precision they are the first choice when doing
    "academic" studies.
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