RTK - Base with Unknown Point - CORS

I am just getting started with Drone Mapping. I have a RS2 and a Mavic 3E Drone. My question has to do with RTK with a unknown point for the base. Many of my job sites don’t have a known point. I believe one solution is to set up the base for an extended period of time and run the data thru OPUS. The issue with this is I don’t always have the time to wait 4 hours+.

If I don’t have a known point, can I use the CORS network with the Base to get my fixed solution? Example: Base is connected to my iphone hotspot and is pulling corrections from the CORS network. The drone is connected to my iphone hotspot to the base thru “Local NTRIP”.

This is where i’m confused. If I use this solution, does the RS2 base even need a ground point for this to work? Does it even matter the height of the RS2 relative to the ground below since we are pulling data from the CORS network?

the good news is my understanding is growing form this community. Im getting close! :slight_smile:

Hi Chris! Yes, you can certainly use CORS to accomplish this depending on your baseline from the CORS to your project site and your project’s accuracy and quality assurance requirements. Can you share these?

If you are relatively close to the CORS, your best bet may be to connect the Mavic directly to the CORS NTRIP. Then your fix it to a likely first order benchmark (depends on the CORS).

If you are at a medium to longer baseline from the CORS and the Mavic has a hard time maintaining a fix directly to the CORS, then you can use a local base (RS2) and use “average fix” to survey in the local base. This can work better for medium to longer baselines because the local base is static and won’t have to reacquire a fix when in motion like the drone might need to do. I’d recommend having the RS2 log the entire session and then run PPK on the baseline from the CORS to the RS2 to confirm the bases position once you are back at the office. This also becomes your documentation for your local base in case the accuracy of your drone survey needs to be evaluated. Note, when you average fix a local base for say 2min, that is the only time the local base needs an NTRIP connection to the CORS. Then the local base stores that position and broadcasts it for the whole session to the drone. It’s doesn’t pass the CORS corrections on to the drone continuously.


Thanks for the help! My Reach View App is telling me that the CORS network baseline is 20-25 miles. Is this distance in range for the RS2? I don’t believe the Mavic 3E’s RTK range is as long as the RS2 correct?

That’s entirely in the RS2 range for RTK. The system is specced to work in RTK up to 60km. One of the main advantages of doing PPK is that you can increase the range to somewhere around 100km and if you go the PPP route, then baseline is irrelevant.

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Hi Chris,

I absolutely agree with the guys above, but want to comment on this your question:

Even if you’re getting a known point for the base with CORS, you still need to provide the base with the best sky view possible. It still transmits data to the drone, so this data quality is better to be good.

And here you can find more info about possible ways to set up the base.

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Just so I understand. If Im using the RS2 as a base to extend the CORS RTK baseline (Drone to Base to CORS Network) Is the height of the RS2 Base relevant ? The reason I ask is I don’t remember seeing the setting to enter this measurement.

So to be clear. The situation is I have a Mavic 3E RTK on a jobsite with no known point. The COPRS network is 20-30 miles away. Since I don’t think 20-30 miles is close enough for the RTK on the Mavic 3E Im using the RS2 as a base that connects to both the CORS network and the Mavic RTK. The CORS network is sending correction to the RS2 since there is no known position onsite and then the RS2 is sending the RTK data to the Mavic 3E RTK. Does the Rs2 Base’s antenna height matter if connected to the CORS network?

I hope this makes sense?

If the goal is to work only from RTK, then the height of the base is not important. When you set it up, it will average over whatever span of time you tell it to, and the resulting position, which is of the base APC, will be what the correction is based on. The drone doesn’t care what height above the ground your base is at as long as it doesn’t move.

The moment a project becomes multi-temporal, then you’re better off establishing your own fixed point on site so you have a repeatable reference for each visit.

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Hi Chris,

Reach can’t transfer CORS corrections to a drone. It sends the data it receives from satellites itslef. In this scheme, CORS acts as a base for your base to establish a known point on a site. Then, RS2 acts as a separate base for your drone. So, the height matters.

Let me better explain my setup.

Mavic 3E RTK - Drone
Emlid RS2 - Base

Construction Site. (Many locations will not have a known point to operate base off of.)
We have a CORS network that is accessible with a baseline of around 20-30 miles±

Setup/ Connection:

Once on site I set up my RS2 Base over an unknown point. This is a location with good sky visibility. I set up my RS2 as a base and and sending Local NTRIP to my Drone Controller. Since I don’t have a known point, I have my RS2 set up to connect to the CORS network for my corrections. I then connect my RS2 to my iPhone Hotspot. I now connect my Mavic 3E Drone Controller to the same iPhone Hotspot and connect the controller to the “Local NTRIP” connection from the RS2. Once connected and everything is dialed in, I get a “Fixed” reading on my reach view 3 app and I get a fixed signal from my Mavic 3E controller.

I start my logging process and then run my flight.

The part that Im confused about is the base height of the RS2. With the way I have this set up, I don’t see where I enter the base height? I did not know if the RS2 Base height mattered since I am getting corrections from the CORS network and Im working off of an Unknown Point.

If the Base height is required can you help me determine how to modify my setup to accommodate for this retirement?

Sorry for any confusion. Im new and appreciate all your help!


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Just because the wording makes me unsure, I want to make it clear that the fixed status of the drone is not related to the fixed status of the base. As soon as the base transmits its own correction stream, your drone will display as fixed when receiving, regardless of the fact your base is receiving corrections from the CORS network or not. So the base could be working off a single solution and your drone would still show fixed.

Basically, you just need to make sure the base mode averaging, while connected to the CORS, is done before you start working with the drone.

Does it really matter? In this case the CORS is only used to correct the base’s antenna position and since there seems to be no permanent or semi-permanent marker on the ground for the base to measure, instrument height won’t have a use.

Hi Chris,

Since I don’t have a known point, I have my RS2 set up to connect to the CORS network for my corrections. I then connect my RS2 to my iPhone Hotspot.

After this step, you need to wait for a Fix in ReachView 3, then go to the Base mode settings and choose the Average Fix option. After that, you can disconnect Reach from CORS cause you’ve already obtained precise coordinates. The unknown point became known.

When using the Avergae Fix method, you don’t need to enter the antenna height.

Gabriel, I meant that the height matters in terms of providing the sky view of the device. If the base position is averaged, then indeed, no need to enter the antenna height anywhere.

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One more small note: if you’re going to post-process the logs afterward, remember the base position that was averaged in ReachView 3 with CORS.

Thanks for the amazing support. This was one major reason I decided to go with Emlid. The devices are great too. :slight_smile:


Thank you for being with us, Chris! :slight_smile:

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