The GPS unit on my boat regularly claims an estimated position error of 4 feet after it has acquired its full complement of satellites. This is a fairly new mid-price GPS unit using up to nine satellites and WAAS. So my recreational GPS supposedly obtains fifth-decimal-place accuracy. It was running under an unobstructed sky, which is common when boating. Careful use of a good GPS unit should be able to achieve this level of accuracy on land as well.
From http://www.gps.gov/systems/gps/performance/accuracy/ the raw accuracy of the positioning information from a satellite is less than 2.4 feet 95% of the time. The accuracy reported by a GPS unit is degraded by atmospheric conditions; false signals, e.g., bounces; and the need to determine position by intersecting the raw data from several satellites. Accuracy can be improved by using more satellites and multiple frequencies and by comparing to a signal from a receiver at a known location. The web page above claims that accuracy can be improved to a few centimeters in real time and down to the millimeter level if a device is left in the same place for a long period of time. I think that these last two accuracies require a close-by receiver at a known location and correspond to what is said in [4]. peter On 08/30/2017 06:53 PM, Nick Wilson (Quiddity) wrote: > On Tue, Aug 29, 2017 at 2:13 PM, Stas Malyshev <[email protected]> > wrote: >> [...] Would four decimals >> after the dot be enough? According to [4] this is what commercial GPS >> device can provide. If not, why and which accuracy would be appropriate? >> > > I think that should be 5 decimals for commercial GPS, per that link? > It also suggests that "The sixth decimal place is worth up to 0.11 m: > you can use this for laying out structures in detail, for designing > landscapes, building roads. It should be more than good enough for > tracking movements of glaciers and rivers. This can be achieved by > taking painstaking measures with GPS, such as differentially corrected > GPS." > > Do we hope to store datasets around glacier movement? It seems > possible. (We don't seem to currently > https://www.wikidata.org/wiki/Q770424 ) > > I skimmed a few search results, and found 7 (or 15) decimals given in > one standard, but the details are beyond my understanding: > http://resources.esri.com/help/9.3/arcgisengine/java/gp_toolref/geoprocessing_environments/about_coverage_precision.htm > https://stackoverflow.com/questions/1947481/how-many-significant-digits-should-i-store-in-my-database-for-a-gps-coordinate > https://stackoverflow.com/questions/7167604/how-accurately-should-i-store-latitude-and-longitude > >> [4] >> https://gis.stackexchange.com/questions/8650/measuring-accuracy-of-latitude-and-longitude > _______________________________________________ Wikidata mailing list [email protected] https://lists.wikimedia.org/mailman/listinfo/wikidata
