Have been doing drone photogrammetry surveys for a while but have never georeferenced them, so am completely new to this.
Looking at getting an RS2.
I need cm absolute accuracy, so from what I can see for RTK, my options for correction are:
Use a base RS2 and put it on a trig point, and a rover RS2 (either with LoRa or NTRIP)
Use a base RS2 with NTRIP connection to a base provider service, and a rover RS2
Use a rover RS2 with NTRIP connection to a base provider service
I can’t really do 1 as I’ll be working alone a lot of the time and can’t leave a unit unattended.
What’s the advantage of 2 over 3?
If I use one of the services, how do I determine which base it uses? Does the service automatically find one based on the location of the rover? I’m in the UK if that makes any difference.
If you have a good source of stations and NTRIP available then #3 is the way to go, but if your baseline becomes too large or you get out of cellular coverage then you will have to have a local base. In that scenario you would either need to post-process the base position to get the absolute global accuracy or traverse in a point from a place that was in cellular coverage and acceptable range from the corrections source. You would use your rover to set a point using NTRIP somewhere at the edge of the coverage area, occupy that point with your base and then shoot in another point from that using RTK over LoRa to your desired location. Whenever you traverse like that it is a good idea to do at least two points so you always have a checkpoint. Option #2 is really not necessary. Once you have acquired a control point for the base there is no longer a need for corrections to it.
Thanks a lot for the reply. Exactly the sort of into I need.
" to post-process the base position to get the absolute global accuracy" - so set up the base and use it to provide corrections to the rover, but those corrections (and therefore the rover’s position) are not accurate until I’ve post processed the base’s position)? Is that setup what’s known as PPK? Is it also an option just to post process all the rover’s positions, rather than the base position?
" it is a good idea to do at least two points so you always have a checkpoint" - what do you mean by that?
Yes, PPK or PPP for the base. If you have a local known monument you can use that as well, but it depends on your region as to how available those are.
Yes, you can log the rover and correct against another source, but that is going to get very time consuming and cumbersome with the more points you collect. You will not be able to do point import and stakeout unless you are getting RTK to the rover.
If you are more than 15-20km (the recommendation I have heard) from the CORS NTRIP or lose cellular and\or do not have a local monument then you would need to get control in range of your site. You can find a monument within LoRa range which in my experience is reliably about 1500-2000ft, but if the conditions are right you can go further than that. Or you can use NTRIP to define a point.
You would then setup your base on that point and set another point on your site or as close to your site as you can get. You’ll want to set a second point so that when you move (traverse) the base to that new point you can check the second point to verify the observation was correct and your new base setup is configured correctly. I would also go back to the point from which you set that new base point, but that is not always feasible because the LoRa may not be good enough going the other direction if the conditions aren’t correct. For instance if the first base point was higher than the new site base point it may have trouble transmitting those corrections back up the hill if the line-of-sight is not as good.
