How to GPS
GPS
GPS systems can provide ~10m accuracy out of the box. By combining samples to reduce noise and using data from other satellite systems (GNSS), we can reduce this variance to ~3-5m. DGPS (differential) introduces corrections from known reference points to reduce variance to ~1m.
RTK
RTK/PPK provides higher-resolution GPS data by pairing a moving (rover) GPS receiver with a static (base) GPS receiver. Conceptually, what we are receiving from a GPS satellite is its location, with an ~1m variance from atmospheric interference, clock drift, and signal multipath. By gathering enough samples from a static GPS (base) receiver, we can estimate the satellite's position much more accurately. Then we can broadcast this error calculation to other GPS receivers (rover) to improve their error calculations as well. GPS L1 satellites are ~12550 miles / 20.2k kilometers away, so having an error estimate from a receiver at a known location allows us to improve our triangulation/trilateration down to the ~1 cm range (+ ~1ppm, eg as the distance between our two GPS receivers increases so does our error). Applying these corrections live is called RTK (real-time kinematics), while doing them after the flight is called PPK (post-processed).
Ntrip
Ntrip is a protocol for streaming GNSS/RTK corrections over an IP network, with a number of public/private providers.
Tools
- Ardusimple -- tools for capturing GPS data.
- Emlid -- tools for capturing GPS data.