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So I watched 4 videos and read a couple how to's and looked at the User Manuals regarding the Phantom 4 RTK and the associated base station.  I'm sort of having a hard time believing what I'm seeing/reading....

Nothing I've seen or read shows the ability to place the base station on a control point with known coordinates and enter those coordinates into the base station (or remote controller).  This means, while the P4 RTK will have phenomenal position accuracy relative to the base station, there will still be a high degree of error for the absolute world position coordinates.  Everything I've seen and read proposes two solutions:

1. Use ground control points, which is laughable as to me the purpose of investing in an RTK drone is to eliminate the need to do that except to do an accuracy check without including the control points in the processing.

2. Connect the remove to a "Custom RTK Network" (term used in the Ground Station interface) which means you don't even use the base station!

3. Use PPK in which case you don't use the base station and you turn the RTK function OFF!

Of the three above solutions, #2 is the "cleanest" as #1 you don't need an RTK drone for and #3, from what I've read the PPK workflow is pretty involved.

Does anyone know regarding #2 what the process is to find appropriate server credentials to input in (flying in the United States?)

 

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 Exactly! This whole mapping thing drives me crazy.  Go  buy this and that gizmo and we still don't have much ato z training which really prepares drone pilots to work, sell and fly with confidence. 

Very frustrating, time to just go back to photography. 

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@Jazee you can actually put in known coordinates in the P4RTK, and can achieve accuracy of down to 5-10 cm without GCPs. 
 

There are 2 issues :

1) the known point must be in global coordinates. 
2) you will have to use the appropriate conversion between ortho height and Ellipsoid height to enter into the base station. 
 

We still prefer using GCPs for accuracy and quality, but it’s still much fewer GCPs and a quicker more efficient workflow. 
 

I don’t have experience with any other PPK drone so can’t benchmark this, but it’s an easier workflow and better results compared to the standard P4Pro

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Do people actually use the Phantom 4 rather than a Matrice with a Velodyne payload? Why would people pay for the larger and more expensive set up if the Phantom 4 with RTK works? Are there some use cases where the Phantom actually can work well?

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I've seen tests where only using GCPs versus only using RTK (with base on known point) the GCP method was actually a little more accurate (when doing ground check with additional GCPs not used during processing.)  If someone is being sent out to establish GCPs having them mark a few more than you would if you were using the P4RTK is not that time consuming.  Doesn't seem like a very wise allocation of financial resources to pay 6 times more for the P4RTK, just going to take more jobs to pay it off  while gaining a modestly more efficient workflow, unless you were doing quite a few jobs a month. 

The latest manuals for the P4RTK actually don't include instructions for setting static coordinates for the base station, nor connecting to an NTRIP caster.  It seems a lot of pilot with very limited knowledge just latch on to the term 'RTK' and what they've read thinking it's got to be 'better' especially if it costs that much more.

Edited by Jazee

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I am now wondering how many pilots out there are using a P4RTK and setting the base station up without known coordinates or ground control points and not realizing they are only getting increased accuracy RELATIVE to the base station position and the  ABSOLUTE world coordinates are still shifted by typically 1-3 meters (X/Y plane) and much higher shift for the Z (elevation) plane?

 

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This post is kind of long. So please be patient. I use the P4RTK all the time. I’ve completed many surveys and use the P4RTK to deliver grading record drawings to my clients, but I use the custom network with GCP. So I think the P4RTK is a great tool for a surveyor or surveyor turned construction manager like me.  But I also work closely with my surveyor in the office as well. It’s definitely a partnership endeavor. I’ve also used the base station but have found it’s not as accurate. My base station does not allow you to punch coordinates directly into the station so I’m not aware of that option. I do have a separate GPS to set my own control for my projects. Either if you use a base station or Custom Network you really need to use ground control. I use “X” amount of GCP for a 40 acre site. But each site is different and control will be different depending on the project site, deliverable parameters and site conditions. I tend to go overboard with my control because I like increased accuracy. Always remember when either using the Base Station or a Custom Network that ever photo is a Control point with the P4RTK. I achieve accurate results because of my process. Less than 1CM of accuracy. Not giving up all my details here. Another factor to take into consideration is the processing software you use. You need to find the software that fits your workflow or you need to change your workflow to match the software processing. It’s not as easy as opening up the drone and flying with the expectation that immediate result to your expectations. Don’t take offense to this but if your not getting results it’s probably because of your workflow and drone processing software you are using. You are probably the problem and not the drone. So no, the P4RTK is not a joke. It’s the real deal but it’s not for beginners who don’t put the work in to get results out. Another factor is 2D vs 3D flight, side and front overlap, camera angle. These are all factors that you need to know and understand. You really need to understand this as part of your process.  So do your research, recon your sites, experiment with GCP. This is a successful tool in your tool box. 

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@MyrtleDrone you can enter the coordinates for the base station.  It's done in the controller app not the base station.  I'm surprised you have a P4RTK and you didn't know you could do that?  Very understandable though since DJI did a complete fail on the documentation.  Users around the Internet have had to discover how to do a lot of things and share the workflow since so much is missing in the P4RTK documentation. The other myth is you cant use a 4G dongle on the base station because DJI never released one.

The known coordinates of the base station can be entered under Main Screen > FLY > ... > RTK
Settings > Advanced Settings > GNSS Coordinate Input.

Secondly, the P4RTK does not add any significant degree of accuracy over using an appropriate number of GCPs.  Many people with a P4RTK use both, they use the GCPs to check the accuracy of the P4RTK photogrammetry output.  This is completely unecessary as you can just use the GCPs alone in the processing and still get the same accuracy with a drone that doesn't have RTK.

https://www.heliguy.com/blog/2019/01/31/dji-phantom-4-rtk-accuracy-confirmed

"With the Phantom 4 RTK, 1.20cm relative horizontal accuracy was achieved. With the Phantom 4 Pro and GCPs, 0.90cm relative horizontal accuracy was achieved."  So GCP only was actually MORE accurate than RTK in this case.

So the P4RTK offers no real benefit in my opinion if you are already laying down an adequate number of ground control points.  If you don't have GCPs, and no known point to place the base station on, in theory, the RTK could provide better *RELATIVE* position accuracy between the geocoordinates that are embedded in the image files resulting in a more accurate photogrammetry output, BUT, it would still have a large error regarding absolute coordinates.  However, it would probably be rare that someone wants cm level "survey grade" accuracy when the absolute accuracy of the coordinates is off buy as much as 150 cm (horizontal) and much more shift vertical.

Really in my opinion, the only benefit for the P4RTK is to improve accuracy in cases where GCPs are not being used for whatever reason.  However for that to work you need at least one known point or you need to do PPK using a remote base station.  If you want to see someone pull their hair out, watch them try to do PPK for the first time with remote base station data.  Then you also have the issue of losing the FIXED connection status during a flight when using RTK - it is quite common to happen for a number of reasons.  You just have to hope a high enough percentages of the images were taken while the RTK had a FIX with the base station as opposed to FLOAT.  But that's a whole other issue for discussion.

I believe the P4RTK, for most applications, is completely unecessary. A lot of the buzz comes from potential users that lack a full understanding of the limitations..  well I heard RTK is "really good", and it costs a lot of money, it MUST be better!  (The case with a lot of products out there being marketed to people.)  The only real benefit is to not have to lay down GCPs and just trust it is more accurate.  Otherwise, you'll get just as good of accuracy laying down the adequate GCPs and using a regular Phantom 4 Pro and incorporating the GCPs into your processing.

 

 

Edited by Jazee

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