RTK accuracy

Since 1 or 2 years, I’m testing some low-cost GNSS receivers with RAW output. The goal is to get a cm accuracy. One way is to store the raw data, then post-process it with the open-source software RTKLIB. I had various fails and success and I finally find a point to place my own reference station, my “base”:

One test was to put the “rover” on my car go back to my home. RTKLIB gave me a solution with “FIX” for a big part of the record : orange is “float” and green is “fix” (best accuracy)

An interesting part is a new roundabout, too new to see it on any aerial picture :

Ok, but what about the accuracy ? So, zoom in, zoom in, ….. zoom more !! Each square is 1 cm. Yes, the accuracy is about 1.5 centimeters !!

RTKLIB gave me a very good accuracy, but is this real ? I can’t answer for this individual point, but with the results I got on surveys points from the French national geographic institute (IGN), I think I can say that the accuracy should be at about 5 or 10 cm, as my base coordinates are not perfect.

RTK vs Aerial Imagery accuracy

We are in September 2017, and the IGN just published new aerial imagery, and they usually do a very very good job. Finally I can see the roundabout I draw on OpenStreetMap 1 year earlier.

Let’s compare my recording and the pictures:

Hey ! Not bad !! Now I must train to drive with a centimeter accuracy :-)

OpenStreetMap database accuracy

I speak about gnss trace accuracy, aerial imagery accuracy, but what about OpenStreetMap accuracy ? I heard that with 7 decimals, the coordinates stored in the OpenStreetMap database get only a 10 cm accuracy. Don’t you think that It’ll be a problem sooner or later ?

Perhaps we should consider adding a 8th decimal ?