I am a UAV operator who is looking to achieve high-accuracy mapping.
My understanding is that, with the use of ground control points and a GNS base station and rover, I will be able to achieve survey-grade accuracy, specifically absolute accuracy. Will the Reach RS2 Survey Kit (2 RS2 units) achieve this? Or is this system different from rover and base systems from Leica and Trimble for instance?
I have also been looking into the purchase of Propeller Aeropoints for this purpose.
Thanks in advance and my apologies in advance for my lack of knowledge on this subject.
I think you would be much better served with the base and rover setup. Remember that you will need a subscription for the aeropoints and it takes them approximately 30 to 40 minutes to provide centimeter accuracy. In that amount of time you could probably set the majority of your ground control points and be done with it. On top of that there is a lot more functionality that you can get into with a base and rover - like PPK when you don’t necessarily need or want to set ground control points or localization if you want to use actual local control. Additionally with that if you are truly trying to present survey-grade “absolute” accuracy you will want to locate hard structures with a rover to supplement your drone survey. The RS2 should be very close to the quality of the Topcon, Trimble and Leica.
I am planning on doing 2-D and 3-D orthomosaics in Pix4D with imagery taken from a drone. I would like to achieve as much absolute and relative accuracy as possible in my modeling. From my understanding, I will be able to get centimeter relative accuracy from the two Reach R2 units and well-placed ground control points.
My uncertainty right now is how to achieve high absolute accuracy of the location of the base station.
I don’t know which type of work I will be focusing on yet (all of the above mentioned by you, lol?) . I guess I need to be as flexible as possible in the beginning.
There are a couple different kinds of accuracies to be aware of.
Site Relative - The site relates to itself accurate and does not have high variations across the site. IE, one end of the project is spot on and the other side is 2ft off. This can be established with RTK/PPK without GCP’s, but you need equipment for the drone itself. With that you should have about the same error across the entire site. This is an “2cm” accuracy that many manufacturers tout, but honestly doesn’t mean a whole lot when trying to relate to ground. If you have this accuracy you can do a 1-point calibration to bring the site to ground elevation, but your horizontal will probably not line up.
Absolute Global - This means that your survey is related to the rest of the world as collected by the satellites on the WGS84 datum. Again this doesn’t relate to the true ground.
Absolute Local - This is what you’re looking for. This means that you are tied to the ground control (with GCP’s) and you can stakeout the 3D surface you create within a tight tolerance.
I use PPK and ground control points and I averaged about 2-3in (5-7cm) by taking the surface from the drone and then going out into the field and verifying the drone survey against the actual ground.
Acquiring locally established elevations is the tough part. If you have CAD knowledge you can easily shift the site to match CAD files, but because Emlid only reports the ellipsoid elevation it will not match the ground benchmarks that were established by a an RPLS crew.
You can find the base coordinates with PPP first, and then just set up Reach RS2 base over a known point, enter the position manually and collect GCPs in RTK.
You can collect GCPs with relative accuracy in RTK and record raw data logs on both base and rover simultaneously. Then you’ll need to use the log from the base for PPP processing to figure out the base absolute position. Knowing this position, you can process logs in RTKLIB to find out the absolute coordinates of GCPs.
I’d recommend using the first one, as collecting GCPs in RTK is much easier than with post-processing.
See if Toronto has a CORS network. If so, all you will need is 1 Emlid as a rover. I’ve been doing 3D modelling for a couple years now. I set up my control points, fly it, process the data with Pix4D then export it into CAD software.
I’m in Massachusetts and our state highway system provides a free CORS network. I get about 0.1’ - 0.2’ absolute accuracy.
Our $hitty state doesn’t offer free CORS or the like… something like $1000 year. They think they are god or something… personally, govt based, it sure as hell better be available to over paying tax payers. Typical govt a-holes and their “toys” they think they own, and tell who can use it if they pay and who cannot if they don’t.
And then you have some states that really offer an over abundance because they know that is best… i got the state that took their ball home.