At 12:10 PM 10/27/1999 -0400, Edward S Light wrote: <snip> >1) GPS-derived positions > > 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- > derived positions quoted to 0.000 001 degrees, which is approximately > 0.11 meters (or about 4 inches), and I wonder about the meaningful- > ness of all those significant digits. (My own coordinates, quoted > in my signature, are given to the nearest 11 meters and were based > on measuring a paper USGS 1:24000 map to the nearest 0.005 inch and > assuming absolutely no errors in the production of that map.) Yes, the term is "SA", which stands for Selective Availability, and the error *I* usually see is around 60 meters or so. Sometimes the satellites get in really good positions and it gets down to around 30 meters, very rarely it gets down to 10 meters. That's why the "(or so)" is in my sig file...<G> Earl Earl Needham, KD5XB mailto:KD5XB@AMSAT.ORG Clovis, New Mexico DM84jk N34d 25.446 W103d 12.700 (or so) Pet peeve: breath is a noun, breathe is a verb (When you take a breath, you breathe...) ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html