M4T RTK accurate or not ..

[Mflyer]

Just a small question, will the M4T be absolute accurate in 1 to 2 cm for 2D mapping with RTK and NTRIP connected? (despite the lack of mechanical shutter)
I reading mixed posts about this.

 

[jaja6009]

No. Unfortunately the T version does not use Time Sync even when receiving corrections.
The mechanical shutter is not the main reason for the lack of accuracy/precision, it's the fact that DJI wants to make you buy both drones if you want to do thermal work and mapping by not having Time Sync on the T.

If you pause for each image you can get it tighter, but when flying a moving mapping grid flight, your horizontal will be the same as normal "GPS" only. The vertical is better and in tests I ran was within a meter for several maps.

You can always place GCPs to get your desired accuracy.

 

[Mflyer]

Alright thank you for the reply. So without Time Sync I quess PPK will also not provide any better outcome.
Would it be possible to use the drone itself to measure out any GCP's if it's RTK/Ntrip enabled ?

 

[jaja6009]

You probably could. In a Baamtech PPK kit for the Phantom 4 Pro v2, you actually used the drone to measure control points. You would place the drone on the target, have an X grid on the screen, line up the centerpoint with the center of the control point and take an image to trigger the PPK time stamp. This kit worked very well. They had measured the offset of the camera and the GNSS antenna.

If you are serious about mapping you would be better off investing in an Emlid or even the DJI RTK 3 receiver. You need to have check points regardless of having RTK/PPK to prove your accuracy. It seems like you already have a source of corrections so one receiver should work.

 

[Mflyer]

Ok :/

 

[jaja6009]

Various places online have this debate. The problem is that not one person has ever produced an orthomap that includes check points to prove their accuracy. There are just claims of cm accuracy with the Matrice 4T, but they don't say whether this is relative accuracy (To scale, does 1 foot in my map measure one foot in reality) or absolute accuracy. Absolute accuracy is the placement of the map to the correct coordinates of reality.

The people saying it has cm accuracy are most likely referring to relative accuracy. When this becomes an argument I always ask to view the quality report showing the RMSE of the check points used. No one has ever posted this.


This debate has gone on since the Mavic 2 Enterprise Advanced came out with an RTK module. I own this drone and ran many tests while receiving corrections and the horizontal accuracy was the same as any drone that does not have RTK. The vertical though was usually around 1 meter or slightly below.

The Mavic 3E and 3T also had this debate.

Another problem is the large file size of the Matrice 4T and Mavic 3T's images. these large files slow down photogrammetry but do not offer better data.
The lack of mechanical shutter is also a problem although a lot of photogrammetry software do have algorithms to compensate for this.

 

[Mflyer]

Hmm interesting. Thank you for the detailed explanation and history of this ongoing topic
This is valuable information in getting a good understanding about the product and it's (mis)information online.
The few tests I did was 10cm horizontal using webODM. Not sure if I done all software settings correctly but the 4T had fix all the time. Another ppk test with Emlid studio which showed 100% single in the photo's and reading your info, this could be because of the missing TimeSync?

Edit: Wait i'm mixing things up. Initially I was putting RTK/NTRIP files in Emlid Studio which is not correct for PPK so later I tested with normal files. The 100% single was however when I added the RTK/NTRIP files as a mistake for the PPK process.

 

[jaja6009]

Hmm interesting. Thank you for the detailed explanation and history of this ongoing topic
This is valuable information in getting a good understanding about the product and it's (mis)information online.
The few tests I did was 10cm horizontal using webODM. Not sure if I done all software settings correctly but the 4T had fix all the time. Another ppk test with Emlid studio which showed 100% single in the photo's and reading your info, this could be because of the missing TimeSync?

Edit: Wait i'm mixing things up. Initially I was putting RTK/NTRIP files in Emlid Studio which is not correct for PPK so later I tested with normal files. The 100% single was however when I added the RTK/NTRIP files as a mistake for the PPK process.

A couple of questions.

When you say 10cm, what is reporting 10 cm?

Next, are you receiving corrections from an NTRIP service such as a CORS or paid service?

When using Emlid Studio are you uploading the obs, MRK and NAV files from your drone? And if so, what are you using for your base?

Here is what you can do.

You can use Emlid Studio.
GOto this site, NGS CORS and find the closest CORS station to where you flew a mission:

ArcGIS Web Application

www.arcgis.com

Next you can download the required RINEX logs so you can PPK your data.

National Geodetic Survey - User Friendly CORS v4.0

Make sure you download logs from the closest CORS for the same time period that your drone was flying. I always download 1 hour before and after to ensure I have the proper coverage.

Use Emlid Studio, use the drone's obs, and MRK files and then use the CORS obs and nav to PPK your data.