So I decided to find out just how good I could get the data from the REACH RS+, particularly when it comes to elevation. Many of our clients are most interested in fast and accurate elevation surveys on construction sites.
Admittedly I regret purchasing the Reach RS+ and will be looking to sell it and invest in the Reach RS2, or another dual band system, but that is another topic. For now I have the RS+ and needed to find out just how good the device can get with a little extra effort.
Step 1. I needed to provide very accurate corrections in real time. For that I setup a NTRIP server on the roof of my house with a high quality dual band antenna and receiver. After collecting raw data during three different 24 hour periods and submitting the data to CSRS, I was able to obtain a very precise x,y,z for my home base station. I published that data to rtk2go.com. By the way, forget about OPUS, I failed on so many occasions to submit data to OPUS with so many random error messages, I finally gave up. The latest OPUS on-going message is that my data is “noisy”, but it isn’t. In fact the CSRS returned excellent data back to me and their graphs do not indicate a noisy signal. But I digress.
Step 2. I put the REACH RS+ on a known location on my property and acquired for 12 hours. I obtained a fix within 30 minutes and go excellent statistics. I used a NTRIP node from rtk2go.com that was in NJ (NJ_Warren). That data over the course of 12 hours produced a poor x,y,x, and the standard deviation was miserable. Not to be discouraged I configured the REACH to use my NTRIP server, NJ_CreamRidge and acquired for 12 hours. This time the data was tight and spot on with the survey point that was established when we had a survey of the property done.
That doesn’t mean much so I set out to 7 NGS points around the area and recorded the results, particularly paying attention to the elevation since that is what we are most interested in. The results (attached) were pretty impressive. In all cases I was within inches of the NGS published elevations, and the X,Y coordinates were within a cm of the published values. I was pretty impressed and comfortable with my calibration and the NTRIP server on my home. I am not sure what is wrong with NJ_Warren, it could be that the coordinate system is not correct, I used NAD83(2011) and I have no idea what CRS they use. But it does puzzle me that their data has a significant error (standard deviation) over 12 hours in the x,y, and z which leads me to believe they are using a single band antenna.
The worst data point I obtained, nearly 4" off the published data does not worry me, that point was taken on a monument located on a narrow shoulder on a road that has significant traffic and is very dangerous. I hurried that measurement, it never went into fixed mode, it was floating. I valued my life more than that one single point. The four last points are NGS monuments that have vertical control, they are the most accurate. I setup the REACH to match the GEOID used by NDS.
I still intend to sell the REACH+. Even though it is accurate, it takes too long to stabilize and go into fix mode, and sometimes it never does. For our work time is important and we need a system that will acquire and fix quickly. I believe that is the biggest difference between a system that has dual band and the REACH+ which has single band. Even with high quality NTRIP corrections it takes forever for this thing to fix under very favorable conditions (30+ satellites, clear sky no obstructions). If anyone is interested, the REACH+ is only a month old and has low mileage.
NGS Calibrations Emlid.pdf (222.9 KB)