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    Re: Eight (or Nine) Mile Chart Error!
    From: Lu Abel
    Date: 2013 Jan 25, 11:42 -0800
    David, one of the reports Richard Langley sent links to mentioned that chart data had been "adjusted" based on "satellite data."  

    First of all, let's remember that no agency of the US government has done surveys and made charts for the entire world.   The NGA re-issues charts of other countries from those countries.  As you might imagine, quality varies considerably  (talk to a cruising sailor sometime about the quality, accuracy, and up-to-dateness of Mexican charts, for example).  I've also read that some of the charts of the Pacific Islands are based on 19th century British surveys!  And that the charted position of some isolated islands have been shown to be off by several miles from their true geographic position.

    From reading the articles, I gain the impression that the NGA attempts to improve the accuracy of foreign charts using satellite images and data.  Apparently something went wrong when the Philippine chart was "adjusted"  That caused the NGA to review all charts where adjustments and corrections made.  A tiny fraction were found to be off, some in the Philippines and a few along the Chilean coast.



    From: David Fleming <d.l.fleming.1---.com>
    To: luabel{at}ymail.com
    Sent: Friday, January 25, 2013 10:31 AM
    Subject: [NavList 22111] Re: Eight (or Nine) Mile Chart Error!


    I find it interesting that in the week since the minesweeper grounding all digital charts have been checked for accuracy and only one significant error has been detected.
    What is the process for cheking the charts?
    Why was that not already done before the grounding?
    Why is it not an ongoing task?
    Dave F
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