CMR+ signals

Measurements - not corrections

If you want to understand how RTK works, you must abandon the differential-correction concept often presented in the elementary how-GPS-works articles and realize that the critical data being broadcast by the RTK base are the L1 and L2 carrier phase and pseudorange measurements (sometimes called observables) from all satellites.

The broadcast data is combined with the same measurements obtained second-by-second at the rover receivers to determine the integer-fixed solution. The accuracy of an integer-fixed solution is at least an order of magnitude better than any solution that can be reliably achieved by simple differential correction.

I noticed that the Trimble CMRx article hyperlinked in the document Gavin recommended slips back into the "corrections" nomenclature, which is unfortunate.

You may want to read Dr. Nicholas Talbot's excellent paper on the Trimble CMR message format, it is well worth the time spent if you want to get into the details. CMR+ was an evolutionary improvement over the original CMR message, so the message is generally the same.

Happy learning!!

GB