Hello
We bought all dji equipment from local dji seller in Georgia country.
During planing mission we always have diferents in elevation 20-25 m. And during data processing in dji terra we have more then 200 m diferent with correct checked cordinates.
We are thinking that our local sellers do not understand survey at all and from begining they should to request d-rtk, - 2 with GNSS system for our country. Wgs 84 but we have something other and we are not able to change it

What vertical datum are you using/comparing to the Z from D-RTK 2 and drone data? What coordinates are you putting into D-RTK 2?

We are using  Lat-Long, we do not have problem with x, y, there is issue with elevation.
Probably issue with Ellipsoid and Geoid.

khvicha688 Posted at 6-3 20:25
We are using  Lat-Long, we do not have problem with x, y, there is issue with elevation.
Probably issue with Ellipsoid and Geoid.

Yes! GNSS data coming in are in HAE. It's best to do your Geoid correction in post-processing IMO. Pix4D and Agisoft can both take care of this.

We can solve this issue and we ca correct it but it takes time on site and in office as well.. On site. I need to check D-Rtk-2 position by other GPS, then I need to i sert corrected cordinates, but I can not enter elevation becouse all time I have more then 20 m diferent and RC do not allow to make chamge in elevation if elevation different is more then 15 m. Same for x, y.. But for this last no issue.
Then in office it takes more time to data processing.
If I use this product and I am paying money for this technical parameters which is written in TDS why  I must do duble job on site and in office

khvicha688 Posted at 6-4 07:58
We can solve this issue and we ca correct it but it takes time on site and in office as well.. On site. I need to check D-Rtk-2 position by other GPS, then I need to i sert corrected cordinates, but I can not enter elevation becouse all time I have more then 20 m diferent and RC do not allow to make chamge in elevation if elevation different is more then 15 m. Same for x, y.. But for this last no issue.
Then in office it takes more time to data processing.
If I use this product and I am paying money for this technical parameters which is written in TDS why  I must do duble job on site and in office

I use the DRTK-2 and M300 with the P1 and L1 with good success. It sounds like you are entering the Orthometric height into RC when you should be entering the Ellipsoid height. DJI uses WGS84 and Ellipsoid heights for all flight planning and RTK corrections so your coordinates need to be in that as well as your terrain file if you are using the terrain following function. Be sure to check which one your other GPS data collector is giving you and then convert if necessary(there should be an option to change your coordinates in your DC). Also be sure to add in the offset for your range pole the DRTK-2 is affixed to (if using the DJI pole that is 1.801 meters).

JesseG Posted at 7-5 07:51
I use the DRTK-2 and M300 with the P1 and L1 with good success. It sounds like you are entering the Orthometric height into RC when you should be entering the Ellipsoid height. DJI uses WGS84 and Ellipsoid heights for all flight planning and RTK corrections so your coordinates need to be in that as well as your terrain file if you are using the terrain following function. Be sure to check which one your other GPS data collector is giving you and then convert if necessary(there should be an option to change your coordinates in your DC). Also be sure to add in the offset for your range pole the DRTK-2 is affixed to (if using the DJI pole that is 1.801 meters).

I have tried to add adjust coordinates by converting Stereo70 (local system) to WGS84 and add the height of the pole but still I am not able to achieve custom network RTK absolute precision.
With custom network I managed to do around 3-4 cm on X,Y and Z of 8-10 cm.

khvicha688 Posted at 6-4 07:58
We can solve this issue and we ca correct it but it takes time on site and in office as well.. On site. I need to check D-Rtk-2 position by other GPS, then I need to i sert corrected cordinates, but I can not enter elevation becouse all time I have more then 20 m diferent and RC do not allow to make chamge in elevation if elevation different is more then 15 m. Same for x, y.. But for this last no issue.
Then in office it takes more time to data processing.
If I use this product and I am paying money for this technical parameters which is written in TDS why  I must do duble job on site and in office

Yes this is also a pain in the bottom for us in Romania. Basically what I do right now is use custom RTK with corrections from the national provider via internet. (you can also buy usb dongle to connect into RC). I do the corrections also in the office, because if I only use the prj from Terra or Agisoft, I will not have cm precision without GCP.
Even with this setup, I still have projects where I don't have cm precision at all even if the report shows fixed position.
For DRTK2 I only tried once but I didn't get the same result as custom network RTK.
I even tried to send to DJI a project a month ago, and today I got a reply that the link is expired and I need to re-upload the project. This is why I came here on the forum, it seems that the support is very lacking.

FlorianGhe Posted at 7-8 03:27
Yes this is also a pain in the bottom for us in Romania. Basically what I do right now is use custom RTK with corrections from the national provider via internet. (you can also buy usb dongle to connect into RC). I do the corrections also in the office, because if I only use the prj from Terra or Agisoft, I will not have cm precision without GCP.
Even with this setup, I still have projects where I don't have cm precision at all even if the report shows fixed position.
For DRTK2 I only tried once but I didn't get the same result as custom network RTK.

When  I  am  using my  equipment  in  high mountains where  there is  no  internet at  this time  we  need  D_RTK-2 base  station with out  it  it  is  impossible  to  work.  if  there is no  internet so  it is  impossible  to use  local RTK.  Several  times  I  disused with  online support time even at  this  time when  I  was  on  site, but  no  any  result.  Again  you  need  to  do  all  correction manually during  data processing  at  office  and  on site  with using  alternative  GNSS station.   

It shouldn't be this difficult. You put the D-RTK 2 on a known point. You enter the Lat Lon in decimal degrees and the Z with the antenna height included in HAE meters. Then it just works. Unless you have faulty equipment.

Or, set the D-RTK 2 up on an unknown spot and follow this workflow:
https://www.aerotas.com/phantom-4-rtk-field-workflow
you'll want some high-precision GCPs (at least one) to allow you to shift the project and improve real-world absolute accuracy.

patiam Posted at 7-12 16:41
It shouldn't be this difficult. You put the D-RTK 2 on a known point. You enter the Lat Lon in decimal degrees and the Z with the antenna height included in HAE meters. Then it just works. Unless you have faulty equipment.

Or, set the D-RTK 2 up on an unknown spot and follow this workflow:

Now  we  are  working  for 500 kV power  line  survey .. length of  line  is 150 km  which  is going through mountains where elevation is  change  from 1500m to  2950m above  sea level.  No internet  connection.
So  to  put new point I  need  to  check  some  point  with  GPS then  I need  to convert GPS coordinates   to  D-RTK-2  coordinates. then  I  need  to  put D_RTK-2 to  know position and insert corrected coordinates from RC. Then  it  requires restart  of  drone and D-RTK-2. and totaly  it  took  me  20 minutes  only  for poor  this  D-RTK on  correct  position.  This is loose  of time   

don't understand "convert GPS coordinates   to  D-RTK-2  coordinates", but regardless, what you described is pretty much the standard practice no matter what type of local base station you're using:

• Establish a new or use an exististing benchmark on site & obtain precise XYZ coordinates for it
• Set up base station over benchmark & enter coordinates
• Wait for precision to reach desired level
• Connect drone to base station and ensure fix
• Fly
  

While the D-RTk 2 is quirky and has its shortcomings, it's no different than other RTK bases in the above respects.

Perhaps you should try PPK if a local base is too onerous for you.

Or maybe a subscription SBAS service.

Or maybe this type of work is just too hard.

patiam Posted at 2022-7-12 16:41
It shouldn't be this difficult. You put the D-RTK 2 on a known point. You enter the Lat Lon in decimal degrees and the Z with the antenna height included in HAE meters. Then it just works. Unless you have faulty equipment.

Or, set the D-RTK 2 up on an unknown spot and follow this workflow:

Hello Patiam, when i write  Z coordinates from GPS antenna third part on D-RTK 2  i must add or remove offset 1,801 m. ?
Thnak's in advance