I just spent a few days surveying with a pair of Facets in very rural western Virginia alongside a licensed surveyor. (No cellular/internet for NTRIP.) At the beginning there were many jokes about my ‘tonka toys’. By the last day his gear was in the truck and we were using my Facets. He said if it wasn’t for them we wouldn’t have gotten most of the work done. He has a pair of very expensive professional but a generation or two old L1/L2 GPS/GLONASS receivers and a 35W radio for the RTK comm link. The current generation (L1/L2/L5 GPS/GLONASS/Galieo/Beidou) is much better. He just wasn’t getting enough satellites in the hollows and valleys to get an RTK fix.
It took me many months of learning, lots of generous advice from my three professional surveyor friends, great support from SparkFun, great firmware upgrades by @sparky and the SparkFun team, and finding a data collection app that works with both the Facets and the licensed surveyor’s office software. The data collection tablet and software cost me 2x what I spent on a pair of Facets.
Surveying is more complicated than it might appear at first. There’s the technical act of measuring, which is just the beginning. Then there’s all the deed research, evidence location, legal precedents, understanding historical survey techniques, etc. etc. etc. that surveyors need to know and deal with. Geodesy itself is also very complicated, and it’s very important to keep your horizontal and vertical datums straight. Geodesy itself it a topic that takes a book or two to explain.
The recent firmware upgrades, especially the functionality added to the base configuration WiFi page, makes the Facet very usable in surveying-type applications. Thank you SparkFun!
I acquired a very sturdy survey tripod, tribrach, puck, and extension to use for the Facet RTK Base. I use a 3.6m survey pole and tripod attachment to get my base antenna (the long fiberglass one SparkFun sells) up high. Extended antenna cable too. I use another survey pole with a bipod for the rover, and generally leave it at 2m. Holybros are 3M velcro & ducktaped to the Facets. I gently twisted the Facet-Holybro cable to protect the individual wires from tree branches that like to pull the pins out of the JST connectors. My Rover got an antenna upgrade too. I keep track of all the instrument heights.
The surveyor flat out said that the one thing limiting the Facets are the radios for the RTK data link. He was happy we got the job done.
I have permanent marks with OPUS solutions for most of the locations I use as RTK bases. Or I set a new base location by RTKing from base with an OPUS solution and back-checking. 20’ or so away from each of the marks for my base locations I have a semi-permanent mark I use as check for my rover at the beginning and end of each day. And anytime I am roving near a known mark I check into it. These checks are important to ensure I configured the base properly and things are working. One transposed pair of digits in configuration the base coordinates and you’re off in outer space.
The radio range is a limiting factor, I get almost 1/2 a mile or so in rolling hills with lots of trees. Not bad for a $100 pair of 100mW radios though!
The area is heavily wooded and the leaves had to fall off the trees for this to all work. The Facets did not work in the summer; but neither did the surveyor’s last generation expensive units. When the leaves were on the trees, I was getting bad RTK fixes. Bad RTK fixes happen even with expensive professional survey gear, so it’s not a uBlox/SparkFun issue. The newer very expensive (US$25,000) GNSS receivers run multiple RTK calculation engines in parallel to check the fixes. Well we aren’t spending US$25,000 on our Facets so it’s amazing what we can do with them. I’ve learned when to get suspicious of the RTK fixes just by looking at the numbers. If I get suspicious on important shots, I will dump (turn the receiver sideways so it loses RTK Fix) and let it fix again, taking multiple shots this way on the same mark.