I was helping a colleague learn the ropes with his newly inherited P4R the other day when we ran into an interesting glitch. He updated all fw to latest versions the night before.

I showed him how to set up and connect to the D-RTK 2 first. That went fine.

Then we went to switch to "Custom RTK Network" (NTRIP). I had him hotspot his phone & get the RC on that connection (this works in the U.S.A.). I walked him through the painful process of entering the NTRIP host adress, port, mountpoint, username, and password. That all went well. He got connected to my NTRIP caster and got RTK Fixed right away. Or at least that's what we thought from the info in the RTK configuration cotrol panel.

When he went to create an autonomous mission and fly it using the NTRIP source for corrections, the main GUI upper left status area showed "Unable to take off - Weak RTK Signal". Also, a red traiangle exclamation popup in the main gui persistently said "RTK Position Error, RTK base station error (0x8400). Please check the base station.,Restart" (this despite being accompanied by the good status message "Network RTK server connection successful"; Fig 1). But when we wentback to the RTK contol panel, everything was still good. Server connected, RTK Fixed, position SD 1-2.5 cm. Even the diagnose RTK showed all green (Fig 2). So either the main GUI or the other was wrong.

Fig 1

Fig 2

We used an NTRIP client on an independent mobile device to verify that my caster was working OK. We tried another NTRIP caster - same behavior. We tand got the same issueried switching back to the D-RTK 2 and got the same issue.
If we turned off RTK completely we were ready to go with uncorrected GNSS(Fig 3).

Fig 3

We rebooted everything and tried again. D-RTK 2 was fine. A/C RTK Fixed Ready to Take Off. Tried to switch to NTRIP and got the same weird conflicting indicators.

Cycled power again and tried NTRIP FIRST this time. Victory! All green RTK happy and ready to fly.

SO: there seemds to be an issue on at least this P4R where you get one shot at setting up RTK per session. It will work with either D-RTK 2 or NTRIP, but YOU CAN'T SWITCH WITHOUT CYCLING THE POWER.

I don't know if anyone else has encountered this, but I'm wondering if some posts here where folks are unable to get NTRIP working might be related...

It's only a job-killer if you don't know the workaround, which is inconvenient but easily doable.

Anyway if you've seen this behavior please chime in...

This is a problem present on all DJI drones equipped with RTK receiver. If you change the reference station without resetting the drone, it no longer works.

There is some semblance of an explanation on the Mobile SDK documentation.


DJI Mobile SDK Documentation

Mobile SDK (dji.com)

Hmmmm-

Thanks LV_Forestry. Has this always been the case, or was it introduced at some time via firmware or something? Because it may be my aging brain, but I'm pretty sure I can recall switching from D-RTK 2 to NTRIP w/o a restart previously, and I know for a fact that I can currently switch between NTRIP casters with mountpoints 100's of Km apart without needing a restart (did so just yesterday). But I intentionally stay a fw release or two behind.
(ETA- from the linked document, looks like maybe switching NTRIP casters w/in the "Custom Network RTK" reference station source might not require restarting, but switching between D-RTK 2 and "Custom" does)

I'm going to test this on my P4R when I get back from the field (don't have it with me- almost never use the thing).

patiam Posted at 2-17 08:55
Hmmmm-

Thanks LV_Forestry. Has this always been the case, or was it introduced at some time via firmware or something? Because it may be my aging brain, but I'm pretty sure I can recall switching from D-RTK 2 to NTRIP w/o a restart previously, and I know for a fact that I can currently switch between NTRIP casters with mountpoints 100's of Km apart without needing a restart (did so just yesterday). But I intentionally stay a fw release or two behind.

From what I can understand from the SDK docs, custom and DRTK-2 are two different protocols, which require resetting the drone to be interchanged.  

I've already had to switch like you did and it actually doesn't work.  I will even go further, with GSPro for the P4M the custom RTK is simply bricked after a switch.  I tried changing the iPad, nothing worked, it's an internal problem with the drone.  With UGCS the custom RTK becomes available again.  Of course I never got an answer from DJI on this subject.

LV_Forestry Posted at 2-17 09:11
From what I can understand from the SDK docs, custom and DRTK-2 are two different protocols, which require resetting the drone to be interchanged.  

I've already had to switch like you did and it actually doesn't work.  I will even go further, with GSPro for the P4M the custom RTK is simply bricked after a switch.  I tried changing the iPad, nothing worked, it's an internal problem with the drone.  With UGCS the custom RTK becomes available again.  Of course I never got an answer from DJI on this subject.

Ugh. I see. I guess I'm misremembering.

Definitely haven't tried the same dance on the P4M w/ GSPro.

Thanks again, I figured somebody (likely you) would have seen this before. A bit sheepish that it's a long-standing issue, but don't recall seeing it mentioned here before.

patiam Posted at 2-17 09:26
Ugh. I see. I guess I'm misremembering.

Definitely haven't tried the same dance on the P4M w/ GSPro.

I usually complain to my local dealer.  In principle, it is his job to report information to DJI.  Sometimes people from DJI contact me back.  But let's be honest they never provided precise answers when the question is very technical.  I just hope that future firmware updates take into account the remarks and that an improvement is made.

I scrapped the DRTK-2 a long time ago.  I've been using National NTRIP and a Trimble receiver for a while.  And recently I switched to all PPK with a DIY Sparkfun kit.  The precision equals that of the preceding systems for approximately 10 times less expensive.  
I install the receiver on known geodetic landmarks.  They are much better off than the base stations.  Data processing does not take much time.  On the other hand, the precision is increased.
What I find fantastic with these DIY solutions is having full access to the configuration.  

Goodbye DRTK-2 problems with its modes and firmware, and the NTRIP with the error induced by the distance

My local dealers rarely have enough knowledge to understand the issue or convey it to DJI (if they would even bother). So I just scream into the nothingness here (actually I never expect anything from this forum beyond the knowledge, advice,  and commiseration/comradery of other users).

Agreed the D-RTK 2 is pretty worthless. I rely on NTRIP almost exclusively. I have my own caster for work around my Uni and we have an extensive system in my state called CRTN with hundreds of CORS stations, so there is usually > 1 close enough and the only reason I don't use NTRIP is when I can't get a network connection. For those cases it is a local base and/or PPK.

Looking forward to checking out the Sparkfun, been meaning to since you first posted about it here. Been relying on Emlid for low-cost RTK/PPK but the Sparkfun is an order of magnitude cheaper, and sounds interesting.Prior to trying Emlid, we were a primarily Trimble shop. Just can't justify the cost anymore given the other options.