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    Re: Sextant Positions versus Map Datums
    From: Jared Sherman
    Date: 2002 Jan 20, 9:22 PM

    >> Does your conversion program make that conversion ? <<
    
    No Bill, the program they supplied does only limited conversions. Unless the 
    celestial system is the same as UTM?
    Here's a quote from the docs on it:
    
    "$ The U.S. Army Topographic Engineering Center (TEC) created a more 
    comprehensive program called Corpscon (Corps Convert), which is based on 
    Nadcon, Vertcon and Geoid96.  In addition to transformations between NAD83 
    and NAD27 geographical coordinates, Corpscon also converts between State 
    Plane Coordinates Systems (SPCS), Universal Transverse Mercator (UTM) and 
    geographical coordinates; thus eliminating several steps in the total process 
    of converting between SPCS27, SPCS83, UTM27, and UTM83.  Inputs can be in 
    either geographic or SPCS/UTM coordinates (SPCS27 X and Y or SPCS83 Northing 
    and Easting).  This program can also be used to convert between state plane, 
    geographic, and UTM coordinates on the same datum.  Corpscon will convert 
    orthometric and ellipsoidal heights in Geographic, State Plane and UTM 
    coordinate systems.
    
    $ Corpscon allows conversions based on U.S. Survey and International Feet.  As 
    of 1997, 19 states have specified, by statute, units of measure for grid 
    coordinates as follows:
    
    U.S. Survey Foot - California, Colorado, Connecticut, Idaho, Indiana, 
    Kentucky, Maryland, Massachusetts, Mississippi, New Mexico, New York, North 
    Carolina, Oklahoma, Pennsylvania, Tennessee, Texas, Washington and Wisconsin.
    
    International Survey Foot - Arizona, Michigan, Montana, North Dakota, Oregon, South Carolina and Utah.
    
    $ Corpscon 5.0 includes conversions based on High Accuracy Regional Networks (HARN's).  "
    
    ======================================
    
    Incidentally--carefully locating the Jones Beach Water Tower on my 1985 NAD27 
    1:20,000 chart shows it to be located 0.3nm away from the current position of 
    the tower that is given in the http://www.ngs.noaa.gov/cgi-bin/ds_mm.prl 
    reference list.
    
    So infosofar as that particular area, more than 1/10th of my position error 
    appears to come from the landmarks being shown in the wrong place. 1/10th 
    down, 9/10th's more to go. It will be interesting to take a (pre-WAAS) GPS 
    to the three area benchmarks that are accessible and see how well it 
    compares.
    

       
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