re: Accurate Lat/Long Info

From: Walter Nissen (wnissen@freenet.tlh.fl.us)
Date: Wed Jun 07 2000 - 07:09:38 PDT

  • Next message: Wayne Hughes: "Re: Unknown Flare and others"

    If you turn on a stationary GPS receiver and record as many positions as
    you can (is that 10 positions per second or 1 position per 10 s?), do
    the positions describe a cube, a rectangular parallelepiped, or a
    truncated cylinder with the actual location at the (precise?) center?
    
    
    rmcconahy@earthlink.net ("Ralph McConahy") writes:
    
    > http://terraserver.microsoft.com/default.asp
    > This site has recently added aerial photos for the full U.S.
    
    Actually, not, so far as I can tell.
    
    > Image not found at the specified location
    > Could not find a USGS Aerial Photograph at location
    > USGS digitized aerial images cover approximately 35% of the
    > conterminous United States. New digitized aerial photos of the United
    > States are loaded daily. 100% of the conterminous United States is
    > expected to be completed by the end of 2001.
    
    He continues:
    
    > After zooming in on your observation location, click "Image
    > Information" on the left for a Lat/Long grid.  You should be able to
    > interpolate to within 0.0001 degrees.
    
    While I also would recommend this as an easy procedure, there are
    detectable differences from the corresponding topo maps.  I think maybe
    the grid lines are not accurately placed.  There shouldn't be a datum
    difference, is there?
    
    I'm guessing that those of us who carry around 4 decimal places may be
    carrying around a little hubris as well.
    
    
    Various authors write:
    
    >  miles ... inches ... PDT ... EDT ...
    
    This is an international forum.
    
    The international unit for length is the meter, together with prefixes
    km, Mm, Gm, Tm, ... , mm, micrometer (micron is a deprecated unit), nm,
    pm, ... .  I haven't looked, but nist.gov should provide extensive,
    authoritative information on units.
    
    The international system of time is UTC.  All (AFAIK) the international
    time services have fallen in line.  Those doing accurate work should
    note that Z = Zulu = UT = GMT runs at a different (unpredictable) rate
    from UTC.
    
    Please minimize your use of obsolete, local, or poorly defined units.
    Unless you use UTC thoroughly (I carry UTC on my wrist, run all programs
    in UTC, etc., etc.), when reporting observations, please provide both
    your local time and your best guess as to the UTC (or, equivalently, the
    defect for your local time).
    
    Over the next few years, people are going to make themselves crazy
    trying to integrate dates from various systems, such as US civilian,
    European, military, etc.  Is 02-01-03 a date in February, January or
    March?  Who knows?  Astronomers and data processors are already
    making extensive use of efficient, logical, internally consistent
    formats, such as 2000 Jun 7 or 2000-06-07, using a 4-digit year.  The
    numeric month is language independent, while the alphabetic month
    provides some useful relief from numeric tedium.
    
    
    In international units, conversion between degree and meter isn't too
    difficult.  In latitude,
    
    1 degree = 111 km   (approx)
    
    = 111.133 - .559 cos ( 2 * phi ) km   (less approx, at latitude phi).
    
    So, .0001 degree = 11.1 meter.  In longitude,
    
    1 degree = 111.413 cos phi - .094 cos ( 3 * phi ) km.
    
    
    AFAIK, there is no program called Quickview.  When I began using QuickSat,
    I began seeing about 3 times as many satellites per evening. 
    
    
    I, for one, would appreciate it if correspondents would send messages with
    no line over 79 characters.  Not all mailers can handle indefinite-level
    wrapping, or wrapping at all.  Even if they can, logging or capturing the
    message can cause trouble. 
    
    And, please don't quote whole messages.  Behavior which is considerate and
    reasonable in a newsgroup, with its more uncertain propagation, is tedious
    and wasteful in a mailing list. 
    
    
    Thanks.
    
    Cheers.
    
    Walter Nissen                   wnissen@tfn.net
    -81.8637, 41.3735, 256m elevation
    
    ---
    
    The use of one or more varieties of VIT (village idiot time) by one or
    more Internet providers in the conveyance of my message to you should not
    be construed as an endorsement of such practice, nor evidence that I may
    be confused about the physical reality of the Earth as an inertial
    reference frame with a unique time system, known as UTC, codified by
    international agreement and incessantly ratified in recent decades by
    uninterrupted, continuous distribution from the various national time
    services.
    
    
    
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