Hello, I'm looking at getting a M4e and a D-RTK3 unit. I'm trying to make sure this will do what I need or should I just look into the Emlid RS3. In watching the DJI videos They mention when you're in Rover Mode you need a 3rd prty RTK Network Account  https://enterprise.dji.com/d-rtk-3/video .  How/where/what is the 3rd party account they are reffering to?

After more research I think I found the answer. Your RTK device dosn't just connect to satilites like your hand held GPS does. You need to choose a NTRIP provider (https://ntrip-list.com/north-america/) and then via a GUI you connect your RTK to that chosen provider. Is there anything else I missed?

You're on the right track. RTK isn't magic. In order to achieve centimetric precision, the receiver needs a source of corrections from a nearby base station. This can be via NTRIP as you described, or from a local base that you set up using a second compatible receiver on a precisely known location. It is also possible to use base station data after the fact to do Post-Processed Kinematic (PPK) rather than Realtime (RTK), if the proper data are logged in the field.

In the case of the M4E (and most other RTK-capable aircraft), if you have an internet connection and a nearby (< 20 km) NTRIP source, you don't need the D-RTK 3 at all (unless you want to use it to map GCPs or something). The M4E RC connects to the NTRIP provider and sends the corrections to the aircraft.

The D-RTK 3 would be used in the scenario where you set up a local base. You provide precise coordinates to the D-RTK 3 and it is then able to calulate corrections and transmit them to the RC/M4E.

Thank you for that info. I've been flying commercial for 5 years and fly primarily constructions sites photo updates. I have created orthomosaics, but they have been for documentation only , no measurements.
I've been asked if I can provide volumetrics for site  work. Would an RTK enabled drone alone connected to a CORS system provide accurate data or is this where GCPs and then an orthomosaic map created with a RTK drone and base station (Emlid,D-RTK3) come into play.

Shusta Posted at 3-7 11:17
Thank you for that info. I've been flying commercial for 5 years and fly primarily constructions sites photo updates. I have created orthomosaics, but they have been for documentation only , no measurements.
I've been asked if I can provide volumetrics for site  work. Would an RTK enabled drone alone connected to a CORS system provide accurate data or is this where GCPs and then an orthomosaic map created with a RTK drone and base station (Emlid,D-RTK3) come into play.

It all depends on what your tolerances are.

If you're doing one-time volumetrics, you can get amazingly good results even with a non-RTK drone, b/c photogrammetry can achieve very internally consistent (but not necessarily real-world accurate)  models, even without GCPs. But if you want to compare your results to other existing data, or do repeat mapping for change detection, you definitely need RTK and/or GCPs.

As to your question, the differences in precision between using a good nearby NTRIP caster and a local on-site base station are much smaller than the differences between autonomous and kinematic GNSS.  Any of the methods to achieve high precision (RTK via NTRIP, local base, PPK, or properly employed GCPs) will work.
But the bottom line is that you (or your client) need to define the acceptable level of uncertainty in whatever it is you are trying to measure, and then do the math to see if it is achievable by the means you have available.

This would be for a client wanting centimeter level accuracy, on a monthly basis. They have talked about 3D models as well for measurements. I have an Autel EVO II Enterprise w/RTK to play with. I'm aware Lidar would be ideal, that's financially out of reach right now. Based on what I read and what you've told me I created a CORS/NTRIP account in my stat and then connect the RTK drone to it. Could I fly the RTK mission and hand the client the images to process? I know they use Pix4D. I guess my biggest concern is without GCPs from the top/bottom of the cut/fill or Lidar what steps are taken to accurately determine a cut pile.

Shusta Posted at 3-8 14:39
This would be for a client wanting centimeter level accuracy, on a monthly basis. They have talked about 3D models as well for measurements. I have an Autel EVO II Enterprise w/RTK to play with. I'm aware Lidar would be ideal, that's financially out of reach right now. Based on what I read and what you've told me I created a CORS/NTRIP account in my stat and then connect the RTK drone to it. Could I fly the RTK mission and hand the client the images to process? I know they use Pix4D. I guess my biggest concern is without GCPs from the top/bottom of the cut/fill or Lidar what steps are taken to accurately determine a cut pile.

If you're not familiar w/ photogrammetric processing and the client is, then yes you can give them the RTK-geotagged imagery to process. That Autel drone is capable of centimetric accuracy when used correctly under good conditions. LiDAR isn't at all required for what you are trying to do. LiDAR's real strength comes in when the scene is complex and includes layering such as vegetation canopy, powerlines, overhangs, etc. If you're doing simple stock pile monitoring or the like, a DSM from photogrammetry will work fine. But if you're doing repeat mapping as you said, RTK or PPK is required unless you're doing lots of GCPs. Even with high-precision GNSS, you'll want to do some checkpoints to assess accuracy/precision.

Thank you again. Like I said earlier I’m looking at getting the M4e while I get some experience with this Autel. Assuming RTK functions as it should how many photos would someone need to calculate a volume (cut/fill)? Would it be just one photo with proper coordinates or would they expect a small orthomosaic of the area to determine. And from what you’ve said GCPs are a must. Since this is a construction site would I pick something that would not be altered for GCP? From what I’m reading the new D-RTK3 should handle my base and rover needs.

To create a point cloud and DSM, which are needed for calculating volumes, you'll need to do a proper photogrammetric data collection flight with highly overlapping photos. There is no way to tell you how many images will be needed without knowing the size of the area, desired GSD/altitude, and overlap settings. If you have an RTK-capable drone, you don't need GCPs per se, but it is good to collect a few for use as checkpoints (CPs). CPs are used for accuracy/precision assessment only, unlike GCPs which are used to georeference the project. RTK can eliminate the need for GCPs, but without at least 1-3 CPs, you have no idea what your uncertainty really is. CPs are collected in the same manner as GCPs. Most folks usefabricor rigid high-contrast targets that are set out before the flight and mapped with RTK GNSS. They don't have to be in the same location for each flight, but if you are mapping the same site repeatedly it can be useful to place permanent targets or use existing features, as long as they are easily and unambiguously identifiable in your imagery and can not move. You can use the D-RTK 3 as a rover to mark targets, but if it is anything like the D-RTK 2, there are much better and more appropriately priced units from other vendors. I have a couple of 2's and never use them for marking GCP/CPs. Hopefully DJI improved on the usability on the 3.

I ran my first mission with the Autel today and RTK.  From what you said about CPs it won't be much use to them.  I can get ahold of CPs from the same person I borrowed the drone from. I ran the mission as low as my surroundings would allow 180ft if I remember correctly with an 80%x80% overlap (which I know is a little much) for a total of 237 photos. I'm running it in WebODM now on Ultra High Quality. I had heard the 2's were pretty useless for this type of work and currently I'm not seeing any useful reviews of the 3's to make a decision.
I'm going to pass the map along with the raw images to the client for them to review maybe it will be useful for this project. Who knows....

So I realized after more research what you meant by CPs and I still need a device(s) for that such as Emlid or D-DTK3. My test did complete due to user error from what I can tell. I'll update this once I have a base and rover scenario.

Yeah CPs are used to assess the agreement of the positioning of your project against independent data that were not used to geolocate the imagery (which is what GCPs do). The method for collecting the positions of the targets/features you use for CPs is identical to that for GCP's; in fact you can collect as many as you like and then use some as GCPs and the rest as CPs, and even swap them around between GCP and CP during processing if you need to. But with good RTK/PPK, really all you usually need are a few CPs, so you can get an estimate of accuracy.
Let us know how your results turn out!

Got it. Thank you for the advise and guidance. I'll update this when I have finally get the opportunity to put all the pieces together.