Hi all,
I have a Reach RS3 and a Mavic 3E RTK, and have access to national CORS service.
Asking myself how to get the most accurate position with this setup for the Mavic 3E, so not talking about GCP’s, only the position of the drone during survey.
Correct me if I’m wrong but the best option would probably be to put the base on a known point (e.g. from national survey) and use the NTRIP stream (via emlid caster) in the drone’s RTK setup?
Next-best option would then be to put the base “anywhere”, connected to the national CORS service, and again use the NTRIP from the base in the drone? Would this setup give better overall results compared to connecting the drone directly to CORS? (…and if so, why?)
Your understanding is absolutely correct. In general, shorter baselines result in higher accuracy and reliability of RTK solutions. This is why it makes sense to have a base station as close to the drone as possible. The position of the base could then be determined by placing it on an NGS monument or by connecting to CORS.
Thanks for your answers!
What I don’t get entirely is how the base station improves the accuracy when connected to CORS and not placed on a known point (eg. national survey). Won’t it just get the same CORS correction as the drone already does?
Martin
The base does not need to remain connected to the CORS. Once you have acquired the point and entered “base mode” the NTRIP corrections are no longer doing anything. The benefit then to local NTRIP is not only have you removed the potential hazard of data connectivity issues but also the baseline from you drone to the base is reduced to a very small fraction of what it would be from the CORS and the residuals on your precisions would be as low as technically possible.
If you have a high level accuracy known point at your location, and are able to set up your base on that point. Then, no need to receive CORS corrections for your base. Just use the published coordinate in your base settings, and transmit local NTRIP to the drone.
If you don’t have a known point at the location is when you would receive CORS corrections to establish your base coordinate on site. And then the rest is the same. Local NTRIP to the drone using the coordinate you established via CORS in your base settings.
2 different approaches for your base depending on your availability.
A third option, if your baseline to a CORS station is too far, is to collect a point via average > single, for as long as you can, and then post process that point later. And then apply those corrections to your drone’s imagery via Emlid Studio.
Hi, thank you all, this has helped me a lot!
Especially your infos when setting up a base station without a known point, only using CORS.
I was somehow thinking that using CORS to establish a known point for the base station, and then using local NTRIP from this base station for the drone would increase the coordinate errors for the drone, since the drone coordinates depend on the local base station coordinates, which again depend on the CORS service.
This seemed to me like a chain where coordinate errors would add up, compared to getting the CORS directly to the drone (always assuming you have a decent baseline distance for CORS).
Martin
This is no different than typical terrestrial land boundary surveys using GNSS.
In a lot of areas in upstate SC due to terrain, there is no cell coverage for RTN. In this case, we normally set up our base with radio RTK and proceed to collect data. We have collected a base point by averaging and accuracy is usually 1 meter. All points collected from the base have relative accuracy to the base (+/-2cm or less).
Once back in the office, it’s a simple matter of either post processing the base data from surrounding CORS using software or submittal online to NGS OPUS. once you have derived an accurate base position, it’s a simple matter of translation of all data to the new base position.
Same format as @dpitman explained for drone imagery translation.
Thanks Bryan,
I see all the use of the base station when CORS is not available or not reliable, or when you have a high accuracy point (e.g. from national survey) available.
Let me rephrase my question:
If you had CORS available with (very) good quality (e.g. short baseline), would you still use a base station or would you ever consider connecting the drone directly to the CORS service?
Sorry if this is all obvious to you guys, but I am learning a lot here.
Martin
If RTN is available and with stable connectivity, yes do it all the time.
I usually use our states RTN either doing terrestrial or aerial surveys. A lot of times when flying I’ll do like @dpitman , @michaelL and just use local connections without any RTN. I’ve always been a post processing kind of guy because I started using GNSS in the mid nineties, that’s what you had to do.
But either way I’m enjoying it in my old age. Keeps my mind active and sharp.
