The fuzziness referred to when talking about GPS position accuracy is technically known as Selective Availability, and yes it is controlled by the US Government. This feature was built in as a way of denying GPS accuracy to non-friendly persons in the event of hostilities (don't want to help them out if we don't have to, right?). However this feature is not used because of the overwhelming number of civilian users of GPS that depend on its accuracy. Also, DGPS (Differential GPS) has arrived on scene and makes selective availability not as effective. As I understand it, future generations of GPS satellites won't even have the selective availability built in. The diagnosis of incorrect datum is probably right on. I've seen up to a kilometer difference on charts in the middle east. As an experiment, go to your closest US Army Corps of Engineers office and ask where the closest surveyed 'bench mark' is and go try out your GPS there. I found a url that answered nearly all my questions: http://joe.mehaffey.com/ Buddy Knox *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Tue Apr 04 2000 - 14:38:50 PDT
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