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"One does not simply use GPS to mark a spot..." I tried this at home and it turns out that easily available GPS devices have huge amounts of error, especially
by foobarian 6y ago
"One does not simply use GPS to mark a spot..."
I tried this at home and it turns out that easily available GPS devices have huge amounts of error, especially without unobstructed line of sight like in woods. I left a phone on a stump recording a walking trail, and it wandered around multiple tens of meters. There is value in what the surveyors do :) Although I guess they would use markers like this as references, so unless they crosscheck with multiple markers and fancy GPS they could make mistakes too.
Edit: and the whole while the GPS receiver is reporting a misleading "5ft" or similar accuracy.
- capableweb 6y agoI'm unsure where in the world you are, but accuracy depends on the satellite you're receiving data from. Commercial GPS satellites (or rather the stream you receive) also have better precision than normal "consumer" ones, and one could assume military has the most accurate ones. The new Galileo (Europe) system has a accuracy down to 1 meter, while GLONASS (Russia) has something like 3 meters. The commercial accuracy of Galileo is down to 1 cm though.
- Twixes 6y agoIs Galileo online?
- capableweb 6y agoYes. Here is the status page for Galileo: https://www.gsc-europa.eu/system-service-status/constellation-information https://www.gsc-europa.eu/system-service-status/constellatio...
- vbezhenar 6y agoHow commercial and normal are differentiated? Is it possible to crack it and use in your own GPS device?
- capableweb 6y agoSeems Galileo has four different services that it offers. Open Service is the public service. If you understand the protocol and radio signals, you can build your own device to read it yourself. High Accuracy Service used to be the commercial service, but is now just called HAS and is offered free of charge apparently. Then there is Public Regulated Service for government bodies, and a Search and Rescue Service.
- skykooler 6y agoPart of it is the difference in the receiver hardware. Survey-grade GPS uses the phase of the signals as well as their timestamps to measure sub-wavelength resolution. This requires larger antennas and much heavier-duty processing hardware, and generally only works when stationary as well, so it's not really feasible for a mobile device.
- aaronax 6y agoThere are two main improvements possible with GPS signals: WAAS gets you to a pretty solid 1 meter accuracy. RTK gets you 1 to 2 cm accuracy.
- incompatible 6y agoThere's also the problem that the land itself is often moving, relative to the GPS coordinates, via continental drift. Over decades, or after a large earthquake, it can add up to metres.
- kumarvvr 6y agoGPS is used in building bridges and marking spots accurate to withing a few cm. But for that you need specialized equipment. https://www.roadtraffic-technology.com/projects/millau_viaduct/ https://www.roadtraffic-technology.com/projects/millau_viadu...