Ich bin auch schon Opfer der Idee gewesen, GPS-Koordinaten aus einem tatsaechlichen GPS-Empfaenger mit moeglichst vielen Nachkommastellen abzugreifen und zu speichern. Tatsaechlich ist schon die fuenfte Nachkommastelle bei handelsueblichen Empfaengern ohne Signalkorrektur schon eher eine ungenaue Angelegenheit:

• The fourth decimal place is worth up to 11 m: it can identify a parcel of land. It is comparable to the typical accuracy of an uncorrected GPS unit with no interference.
• The fifth decimal place is worth up to 1.1 m: it distinguish trees from each other. Accuracy to this level with commercial GPS units can only be achieved with differential correction.
• 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.
• The seventh decimal place is worth up to 11 mm: this is good for much surveying and is near the limit of what GPS-based techniques can achieve.
• The eighth decimal place is worth up to 1.1 mm: this is good for charting motions of tectonic plates and movements of volcanoes. Permanent, corrected, constantly-running GPS base stations might be able to achieve this level of accuracy.
• The ninth decimal place is worth up to 110 microns: we are getting into the range of microscopy. For almost any conceivable application with earth positions, this is overkill and will be more precise than the accuracy of any surveying device.
• Ten or more decimal places indicates a computer or calculator was used and that no attention was paid to the fact that the extra decimals are useless. Be careful, because unless you are the one reading these numbers off the device, this can indicate low quality processing!

Ich war damals so blauaeugig, acht Stellen anzugeben. Wuesste ich heute natuerlich besser 😉

Was das mit der Signalkorrektur und HDOP und sonstigen Dingen auf sich hat, laesst sich auf Kowoma.de nachlesen.

(via)