Hi, my company recently just purchased a set of RS2 survey kit. I am new to this GPS and I’m not sure how to use it. We are using it to take the points for cable detection works and also Ground Penetrating Radar (GPR) survey.
Set up all the things according to the youtube videos, but the accuracy somehow is off by few meters. So I used two ways to check the accuracy:
Take the points and input in a topo survey drawing, as I believe topo survey should be nearly 100% accurate.
Compare with the points taken by Trimble R10, as we already have existing R10. By right RS2 should be more accurate as Trimble R10 is centimeters accuracy, RS2 is millimeters accuracy (according to what I saw on internet). But somehow all the points taken with RS2 is off by few meters, while the points taken by Trimble R10 is very accurate.
I’m not sure is there any error within the RS2 setting or because I didn’t not subscribe to any NTRIP service. From what I saw from the website: Reach RS2 needs a base station as a source of corrections. That’s a requirement for centimeter accuracy in RTK and PPK. Base might be either another Reach RS2 receiver or an NTRIP service.".
So I suppose if i already have one RS2 as the base station to act as the source of correction, whatever points taken by another RS2 receiver (rover), if I get a FIX solution, it should achieve at least centimeter accuracy right?
Please correct me if I’m wrong.
How did you setup your base, average single or manually over a known point?
A rovers fixed data is only as accurate as the corrections it receives from a base. All data is relevant to the base stations location Lat/Lon/Alt. If any of those are off, your rover is equally off by that much.
If you have a known point, do a manual setup and input the LAT/LON/ALT then test again. It should be very close then.
I set up the base by average single. Does it mean if I didn’t input the correction to the base or didn’t input known point to the base, all the points taken by the rover will not be accurate? Normally I wouldn’t have a known point if I were to carry out the work at the site.
Ok, as an example, take your Trimble R10’s back to the same site and set it up and then read in the data to your software. You will again see an obvious difference. If you were doing post processing, you could get the data to match.
RTK gives repeatability and accuracy. One thing a lot of users do not understand is everything is relevant to the base station being used, in particular if you are doing a single average with no post processing. Single average, depending on how long you average, can be up to 3 meters off on Latitude/Longitude and up to 10 meters off on Altitude.
If you go back to the exact same location and setup your RS2 base average single, take the same shots with your rover, you will again see a difference in the data. Average single has a huge difference in data from one day to the next. Even though the unit is in the exact same physical location, due to the accuracy of single average, the RS2 gets a different Lat/Lon/Alt. If you record the Lat/Lon/Alt and setup the base the next day in the exact same position but use manual setup and input the Lat/Lon/Alt your points will match almost perfectly as yesterday and today, they are using the same reference station.
When trying for repeatability/accuracy your base station needs to be surveyed in. One way is a known point to surveyed accuracy and manually setup your base station directly over it and adjusting the Alt or Ht for the tripod/GPS receiver difference. This places your base true which will make your rover true.
The other is post processing data. To hard to explain in just a paragraph.
If you have a NTRIP service their base stations are normally surveyed in. Setup your base using fix average for 5 minutes or so and it will get it very close depending on how far your base line is from the base station. Farther from the base, increase your average time.
In theory, the R10 and RS2 should have similar accuracies, the only meaningful difference being the price you paid for the units.
If there is no known point where you will be, you can follow this guide to find a very precise position for a temporary point you can establish at your projects.
Then it’s only a matter of letting your base sit for several hours on that point to gather enough observation data for PPP while you make your measurements in RTK with the rover. Of course, the initial RTK survey will be off by a few meters if you do a single average for the base position, but that can be post-processed after the fact using the results of the PPP service you used to find the correct base position. If you return to that project site later, you now have a precise base position so you can do a manual base setting and get millimeter/centimeter RTK without having to post-process anything.
