G'day from Australia,
we have been using a Phantom 4 Pro V2 to measure stockpiles using Drone Deploy.
We are now wanting to expand to cut and fill measurements over a relatively large area, the Phantom RTK seems like the next natural upgrade to ensure accuracy.

We are very remote, no phone reception or NTRIP signal. We are not surveyors so don't have any other gear to mark 'known' locations. The reason we are looking into this is that it cost so much to get surveyors out here quarterly.

A couple of questions:
1. will the P4RTK setup work with high accuracy without NTRIP or phone reception? We are not in a hilly area, just remote.
2. will the fact that we dont have a defined point make any difference - we are only looking for relative accuracy, not global.
3. in the future, if we wanted to survey out defined points onsite (eg. for boundary lines) what other equipment would we need to use the base station as a handheld mapping device?
4. what program do you use for surveying with drones?

Many thanks in advance,

Joe

If you are only looking for relative geographic accuracy, the ordinary P4 pro should be just fine.
4.  I use DroneDeploy for the flight planning and image acquisition and Agisoft Metashape for processing the data/images.

Labroides Posted at 5-25 21:49
If you are only looking for relative geographic accuracy, the ordinary P4 pro should be just fine.
4.  I use DroneDeploy for the flight planning and image acquisition and Agisoft Metashape for processing the data/images.

We use contractors onsite and they would get paid according to the data collected so we have to show that it is verifiable and repeatable which the P4 over an area that size is not (according to what I have read). The total site is 81ha.

1. with p4rtk AND drtk2 you will get precise orthophotos or dem (or better than P4V2),  but not accurate if you cannot measure at least 1 GCP. With no cell phone you should PPK with a GNSS
2. Ok, this is what i meant in 1). Rellative accuary there´s no need for ppk or gnsss. But remember to use DRTK2.
3. Wich base station? drtk2 is not actually a useful for gnss surveying, and you cannot consider the RC as a handheld mapping device. You will need a GNSS and a controller.
4. metashape

Hey this YouTube video might: https://www.youtube.com/watch?v=h26_gi_-8Rw

inspectorherb3 Posted at 5-26 14:40
Hey this YouTube video might: https://www.youtube.com/watch?v=h26_gi_-8Rw

I understand GCPs although I didn't realise I needed them to confirm RTK results.

The reason I want to use the base station as a handheld mapping device is that I'd like to mark GCPs with it if I can get 4G signal.
Anyone any idea on how to use the base station as a handheld mapping device?

Hi Joe,
If the area studied is known and is always the same, it is possible to have geodetic markers put up permanently by surveyors who will then be used as GCP.
You can also put its permanent markers yourself if you don't need precision in space but rather precision between each repetition of measurements. Because as i undertsood you are more interested by the volumic data of the stockpile than the position of this stockpile.

Depending on the surface and the number of markers it will certainly cost you less than having a Trimble or Leica antenna, a subscription to a RTK / RINEX service ...
Then with your P4RTK I'm not even sure you need a DRTK-2. In Metashape you will be able to align your 3D models and make the comparisons directly to obtain surface and volume according to the GCP position.
It only works if the ground is stable. If these are soils likely to change shape with humidity then this will not be possible.

After the question to buy a P4RTK or a P4P!
I think it's worth trying with a P4P and fixed GCP.

I have the same problem in some forest where it is not possible to synchronize the RTK, Trimble and P4. This technic of permanent GCP works extremely well. it takes a bit of work in Metashape to identify the GCP (Instead of the few GCP usualy when RTK is active). I use plastic sticks made to mark the cadastral plots and be able to retrieve the place where to put GCP.

Results is as follow : horizontal and vertical precision on the ground and wood piles is +/- 5cm.  On the treetops +/- 50cm. this comes from the resolution of the sensor, top of tree are thin and moving with wind while drone is scanning the area.

Good luck !

Jordane

Labroides Posted at 5-25 21:49
If you are only looking for relative geographic accuracy, the ordinary P4 pro should be just fine.
4.  I use DroneDeploy for the flight planning and image acquisition and Agisoft Metashape for processing the data/images.

[Edited to add: I concede that the below response did not take into account the OP's statement that he is OK working in local non real-world coordinates. My statements are more applicable to working in real-world coordinates.]

This is not correct if the OP wants to do repeat measurements, ie change detection (which sounds like what he's after), unless his required precision is < the uncertainty of autonomous GPS in his area (which is probably at least 2-5 m XY, and much worse in Z).

Without GCP's or some other way of accurately co-register his orthoimages & DSMs, the error will compound with each repeat survey.

Using RTK or PPK will get his error down to a few cm for each survey, rather than a few m. This will be much more likely to yield meaningful results for something like cut & fill calculations.

To answer OP's question: if you can get a professional surveyor to just place a few markers in your study area(s) and provide survey-grade accuracy coordinates for them in your chosen datum, then you can locate the D-RTK 2 on one of them during your surveys and enter the precise coordinate into it. The rest you can use for GCPs and/or checkpoints by placing targets on them that will be visible during the flight. Using the D-RTK 2 in this manner requires no NTRIP or external internet connection of any sort. The caveat being that you need to remember to sign in to your DJI account from the P4R RC a day or two before your flight or you won't be able to fly (assuming no connectivity from flight location).

If you use the D-RTK 2 as your base station but do not put it on a point with precisely known coordinates, your accuracy will be better than the autonomous GPS on the P4 V2, but still in the neighborhood of 1-1.5m or so.

In its case, GCPs with constant locations (If the ground is stable! do not do this on a peat bog for example) and a P4Pro do the trick. In Metashape it works very well.

After that if he wants a perfect georeferencing in his datum that's another story. In this other case yes, it will be necessary to use RTK / PPK to get accurate data.

I regularly measure piles of wood to control their settlement, few GCPs paint around each pile makes it especially easy in Metashape. I mark them as GCP with the same references each time, the alignment is perfect, the volume measurement too. No need to take out the GNSS antenna. If I understood correctly Joe seems to be in this configuration as i understood. Maybe I'm wrong !

Joe to tell us more!

LV_Forestry Posted at 5-27 09:15
In its case, GCPs with constant locations (If the ground is stable! do not do this on a peat bog for example) and a P4Pro do the trick. In Metashape it works very well.

After that if he wants a perfect georeferencing in his datum that's another story. In this other case yes, it will be necessary to use RTK / PPK to get accurate data.

Yes, the P4P is fine IFF he has precisely positioned GCPs and uses them correctly (and stable ground, as you mentioned). This assuming he wants to relate his results to anything else with real-world coordinates.

So, whatever aircraft he uses, he needs to have a surveyor create some benchmarks for him, or buy or rent the gear to do so himself, after learning how to use it.

With the P4R he will be able to use all or some of his benchmarks as checkpoints rather than GCPs, so he will get a more robust measure of positional accuracy than with GCPs alone.

But bottom line is yes, if he wants to work entirely in arbitrary local relative coordinates, he can do as you described.

What a fantastic forum - thanks for the replies.

Unfortunately, we can't use the surveyors as they have refused to do permanent GCPs (as they know we need them to do drone surveying and therefore stop using the surveyors - job security!). They also point out that we would need to place GCPs at the bottom of active pits regularly to accurately get heights - which is right. So using the surveyors to give us GCPs is out of the question (and frustrating!).

Ultimately, I want to have my cake and eat it with minimal gear. I want to be able to mark GCPs and then fly RTK with the P4RTK and D-RTK 2. I'd like to be able to mark the GCPs with the D-RTK 2 as a handheld mapping device. We need the accuracy for bill and legal purposes.

I do have NEW info. We are putting in a fixed internet satellite connection that you can connect with wifi onsite. Its a big site so I might not wifi on the far end (extender?), but the base station could be setup and connected to the internet. If this is the case, could I get a NTRIP type signal to the D-RTK 2 and use it as a handheld mapping device for GCPs?

Hi Joe,

I suggest you send us the coordinates of the site, specifying the area covered by the internet connection and the area to be studied. From that I (and maybe someone else too) will watch the last known DTM, and I will tell you how I would proceed.

This will only be my opinion, but this may be a starting point for more comment.

I know what it's like to get recommended gear that's worth a fortune, to buy it, and to realize that it's totally useless! The idea is to avoid that!


Jordane

JoeMcBrien Posted at 5-27 17:55
What a fantastic forum - thanks for the replies.

Unfortunately, we can't use the surveyors as they have refused to do permanent GCPs (as they know we need them to do drone surveying and therefore stop using the surveyors - job security!). They also point out that we would need to place GCPs at the bottom of active pits regularly to accurately get heights - which is right. So using the surveyors to give us GCPs is out of the question (and frustrating!).

you'll need to check to see if the D-RTK 2 sold in Oz can use a WiFi connection for NTRIP corrections in Mode 3.

P4Rs sold in different regions have different capabilities, not sure about the base. See the attached User Notes pdf for more info.
Assuming the kit will allow it, you won't need net connectivity throughout your  study area, just throughout the area where you wish to place GCPs (and your base).

Even w/o a net connection, you may be able to log data on the D-RTK 2 and PPK process it w/ data from a CORS to get a very accurate loaction for where it is, and use those coordinates for it during your flights ("real" RTK receivers can do this; I haven't tried it w/ the D-RTK 2). Then you won't need NTRIP. Could do same for benchmarks on which to locate your GCPs.