A good explanation of base stations and RTK

[Simon Ritchie]

I've found a very good explanation of how base stations and the RTK protocol work.  It has nice clear diagrams and goes through some very basic stuff.  

As I mentioned in another posting, a lot of Lidar scanners depend on a base station.  The base station sits at a fixed point on the ground so it can find its own position very accurately and it then uses a radio link to hep the scanner get a fix.  I've always been a bit puzzled as to precisely how they work.

The explanation I found is in the online manual for the Emlid's Reach system:   https://docs.emlid.com/reachm-plus/common/tutorials/rtk-introduction/

Somebody mentioned to me that the base station sends a constant stream of corrections to the scanner, and I never understood why.  Having read this manual I finally got it.  The base station and the scanner are constantly using satellites such as the GPS network to get their positions.  The positions they get are always inaccurate, and each one is differently inaccurate.   The base station is fixed in one position and over time it can correct the errors and gind its own position to within a few centimetres.  The scanner is fairly close to it and (crucially) receives the same signals from the same satellites.  The base station gets a slightly inaccurate position from the satellite and tells the scanner how to correct it.  A fraction of a second later, it gets a different inaccurate position and tells the scanner how to correct that, and so on.  Simple.

The Reach system is a cheaper alternative to the "traditional" base stations, costing a fraction of the price.  I haven't tried it yet so I can't vouch for its utility, but the manual is great!