Re: GPS Question

Robert G Fenske Jr (
Wed, 27 Oct 1999 17:47:36 -0500 (CDT)

On Wed, 27 Oct 1999, Edward S Light wrote:
>    I recall that, at least a few years ago, coordinates obtained from
>    the GPS system were intentionally degraded (I believe the term was
>    "SA"). If this is still true, what is the approximate magnitude of
>    the effect? Centimeters? Meters?  Worse? One frequently sees GPS-

	That is still the case.  With Selective Availability (SA), also
called the Standard Positioning Service, an ordinary user can expect 100
meter position accuracy 95% of the time.  Differential GPS, a technique of
using two GPS receivers coupled with an already-known position can easily
get meter-level accuracy (as I have done with my office) and with enough
processing centimeter-level accuracy.

Robert Fenske, Jr.    Sw     |The Taming the C*sm*s series:
Southwest Research Institute            /R---\  |
Signal Exploitation & Geolocation Div  | I    | |"The Martian canals were the
San Antonio,Texas USA  ph:210-522-3931  \----/  | Martians' last ditch effort."

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