Hi All!  I've never used RTK and I'm not a surveyor.  However, I've seen lots of courses that talk about GCP's and the use of surveying gear to get readings on those points.  Is there a device that has both RTK and can be used for these GCP?  Sorry if this is naive.  I know both devices can be pretty spendy.  Just trying to make the investment more "useful".

Hi,

There are a few things to consider before buying a GNSS receiver.
The budget and the precision are the main ones.


1st Solution, the zero cost:
The method consists in creating a support that can receive your drone equipped with RTK. You drill a hole under the support which must be in the axis of the camera of the drone. You put the center of the GCP in the middle of the hole. You take a photo with your drone and the RTK FIX. Then you just have to extract the EXIF coordinates (Agisoft have a dedicated function for that), remove the distance between the camera and the support, and voila! accuracy +/-5cm guaranteed. I made one for my P4R in case my receiver runs out of battery. It's more of a workaround than anything else (Receiver' battery failure...), but it gets the job done.

2nd Solution, the low cost:
SparkFun GPS-RTK-SMA Breakout - ZED-F9P (Qwiic) - GPS-16481 - SparkFun Electronics
If you have some knowledge to assemble development boards, there are plenty of tutorials on the internet. I make custom GNSS receivers from this board. Accuracy +/-1.5cm Horizontal and +/-2cm Vertical. You can also use it as a base station to cast NTRIP or save OBS files for the RINEX/PPK.

3rd Solution, the low cost +
SparkFun RTK Facet - GPS-19984 - SparkFun Electronics
It's the same board as the previous one but it comes pre-assembled and configured. All you have to do is download SWMap on your phone (Android yes, APPLE not sure and never tested). To take GCPs without breaking your bank account, this is the ideal tool. The precision is the same as the previous one.

4th Solution, For low budget surveyors
S580 GNSS Receiver - Stonex
We go upmarket, there are more features. Calculation of distance, area... The precision is the same as the two previous ones.

5th Solution, For Surveyor
Trimble R12i | Trimble Geospatial
The functionalities are very advanced, and the precision is according to the manufacturer a bit better.

All these solutions require a stable connection, via GSM/4G, WiFi, Radio... on a base station located at a reasonable distance. Beyond 30-35km the quality begins to seriously deteriorate.

My best advice, if you don't intend to open a surveyor's office, just take GCP points, invest in the low cost + solution.
Also, if you have to take GCPs under the canopy, go directly to the Stonex receiver, it works pretty well in the forest. I have the Trimble R8s (discontinued), honestly I'm constantly looking for open spaces to get a FIX. Even my low cost DIY has less trouble fixing RTK. Test carried out with identical settings. Of course if you set +/-5m instead of +/-5cm, all the receivers will fix.

If you decide to invest in high-end equipment, ask to try first. Because Trimble is good, but it's also quickly complicated for everything. Once I broke the screen, it was a nightmare to get the license transferred to another device. It's more a reseller's problem than Trimble's, but what I mean is that with a low cost Sparkfun antenna, there's no such hassle.

And finally you need to know what coordinate systems you are going to use. You can configure your receiver in UTM, that is to deal with coordinates in meters instead of degrees, it is more readable. This is only my opinion, I have a certain colleague who prefers WGS84, I don't judge! You will need cadastral markers to calibrate your instruments, but I understand that the geography agency in the US is quite efficient, this should not be a problem for you.

Below is the support of the P4R. You have to put the landing gear in the slots and against the stops. The center of the GCP and put in the middle of the viewfinder in the center of the support.

WOW, that's tremendously helpful... and it points out how much more learning I have to do.  Of course I knew it was fairly complex, but this is yet another huge complexity leap in my droning journey.

Perhaps this is a stupid followup question, but could the DJI D-RTK 2 base work for these purposes as well? I know it's "meant" for RTK, but does that mean it could accurately help mark GCPs as well?

kapchur.us Posted at 1-26 05:05
Perhaps this is a stupid followup question, but could the DJI D-RTK 2 base work for these purposes as well? I know it's "meant" for RTK, but does that mean it could accurately help mark GCPs as well?

In mode 3 yes it is possible to measure points.  But you also need a P4R radio control with GSrtk.  The one with the integrated screen. Maybe it works with other RC, not sure.

The DRTK2 is good if you are in an area without a GSM network, therefore without NTRIP.  you can then place it on a known geodetic marker and use it as a base station.

Some use a GNSS receiver (mentioned above) to mark a point to install the DRTK2 there.  If you have NTRIP available to mark a point, don't bother with DRTK2, just use NTRIP on your drone.

But not with the M3E controller?

kapchur.us Posted at 1-26 07:14
But not with the M3E controller?

I have no information about that. I will see if i have colleague nearby with DRTK2 then i can try. Or moderators could answer it will be faster. But i guess the answer will be no since it was a GSRTK feature. Not Pilot.

Thanks LV_Forestry for all that! It looks like the Facet is the way to go. I get how that marks GCPs. Will it also communicate with the M3E RTK module and provide the correction data while mapping? That's what I imagine the DJI base station is supposed to do. Maybe that's overkill for what I want to do (not surveying anything) but if I'm mapping, say, a river valley and I can't get down there to set visible GCPs within the mapping route, I reckon I'd want that RTK correction data sent to the drone. Apologies for sounding naive but this is new rocket science!

djiuser_4344uphz4RDO Posted at 4-21 11:01
Thanks LV_Forestry for all that! It looks like the Facet is the way to go. I get how that marks GCPs. Will it also communicate with the M3E RTK module and provide the correction data while mapping? That's what I imagine the DJI base station is supposed to do. Maybe that's overkill for what I want to do (not surveying anything) but if I'm mapping, say, a river valley and I can't get down there to set visible GCPs within the mapping route, I reckon I'd want that RTK correction data sent to the drone. Apologies for sounding naive but this is new rocket science!

You're welcome.
Facet is good but be sure to have an NTRIP network available. Otherwise you will enter the tortuous world of PPK and PPP, it is not too complicated but it requires a certain rigor in the survey. Feel free to ask.

Guten Morgen,
ich wollte einmal nachfragen ob die D-RTK Mobile Station sich mit der Fernbedienung der Phantom 4 - GL300E - verbinden lässt.
Kann mir dort einer weiterhelfen?

djiuser_pbZuEuC3nkmc Posted at 2-17 00:43
Guten Morgen,
ich wollte einmal nachfragen ob die D-RTK Mobile Station sich mit der Fernbedienung der Phantom 4 - GL300E - verbinden lässt.
Kann mir dort einer weiterhelfen?

Which phantom version ?
Pro no
RTK and multispectral yes

Vielen Dank