It is not uncommon for surveyors can measure down to the mm using static equipment and at the cm level for dynamic measurements. Google for "real time kinetic" RTK. Positioning can be done real time or data can be logged and then post-processed. For these accuracies you need a receiver that can receive both the L1 frequency (Civil) and L2 (Military) to cancel out some of the ionospheric time delay effects as well as a stationary reference receiver within roughly a 100 km radius. Receiver designers are getting quite smart with their algorithms. While the receiver is not able to fully decode the L2 signal it is able to obtain enough information from it to be useful. No special licence is required, only a significant amount of cash. High quality receiver/antenna systems would set you back $20 - 30 K a few years ago when I looked. Even consumer GPS systems can determine position more accurately if you can extract the pseudorange, carrier and doppler information from them and then post-process it. Regards, Gordon Williams ----- Original Message ----- From: "Alan B. Pearce" To: "Microcontroller discussion list - Public." Sent: Monday, March 26, 2007 3:53 AM Subject: Re: [EE] Swiss pilot achieves his flight of fancy > >> For a few thousand the surveyors here in the states are > >> supposed to get accuracy down to inches. > >> > > > >Yes, but to get that kind of accuracy they leave their GPS > >receivers listening for hours averaging out the errors over > >time. Not the case here. > > I always understood they were licensed to use the high accuracy data stream, > not the normal one used for consumer GPS. They certainly cannot wait around > for ages to get an average done. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist