Thoughts on the Phantom 4 RTK

May 6, 2014
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I sure wish you would add a P4RTK to your arsenal!
Ha! I'm willing to do the testing if someone wants to send me one! I haven't mentioned what we have because I didn't want to seem like a corporate shill, but we've got AirGon's Loki system for our P4P and M200 multirotors and an eBee Plus RTK. We finally got our eBee back out of the box this week for some pre-roadtrip testing and I was extremely delighted to see that I hit a total of 10 aerial targets at less than 0.1' RMSE when only using the PPK geolocated images (no GCPs). Yes she's expensive, but that system really works!
the biggest drawback (for me) is having to use the DJI GSR app
As I've commented before, I really wish DJI would get their software up to speed with their hardware. I've heard that terrain following is coming out at some point; that's the one that could possibly push us to convert. The Loki system can only use the GS Pro app due to the way that it post-processes the camera event data, so it's a major limiting factor for flight planning. If DJI were to open up their internal data file generation to 3rd parties, you'd likely get a lot more app integration. We've also got an XT2 that isn't compatible with any of the mission planning software, including GS Pro, and I haven't seen anyone attempt to integrate the large capacity batteries into the mission planning stage.

What would you include in your app?
Nov 2, 2013
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Olympic Peninsula USA
Dave - As an engineer and surveyor, you won't catch me picking sides in that fight. But I have experienced much of the same here. Like you were considering, to prove your accuracy to the surveyor, see if you can fly a project they have already ground surveyed. Georeference it with photo-identifiable points from the survey. Then overlay their ground-surveyed points onto your orthomosaic. Hopefully that will help prove its value. It is also a great way for you to test your methods and the results you are obtaining from your processing.

Thank you, Sir!
Mar 27, 2016
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I am also surveyor engineer and have done various tests with P4 standard. I haven’t had the opportunity to test a PPK or RTK drone but the main problem for me is that the positions of the photos are interpolated due to the rate the base station sends data. Most COORS or user base stations send corrections at 1hz rate therefore the fast moving drone must work at 5 to 20hz in order to keep up. Then the processing software interpolates the measurements to determine the position of the camera at certain time. If a user has his base station and rover(drone) work at 20hz maybe the positions are more precise.
Anyway with P4 and GCP’s I use 80% front 75% side lap at 40m and using terrain awareness with MapPilot usually I get very good results. Sometimes I use double grid missions for even better results.
Just my 2 cents.
Dec 11, 2016
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I need to check out the GSR app before writing it off completely, but it looked like a pretty basic grid mission planner.

One problem of several mission planning apps is that the aircraft stops at each turn. Using Litchi, I am able to round off each turn and never change the speed of the drone. This speeds up that mapping process considerably and lets me map the most area in the least amount of time.

I map linear roadways frequently. When doing this, I usually need to pick up extra width when side roads intersect the main road. For instance, I may need a 300' width on the main road, but I also need 500' length up the side road. Litchi allows me to customize my mission to handle this in one mission.

And to eliminate missed photos that occurred in some apps, I switched to shooting photos at a constant interval (2 or 3 seconds) and set the speed of the aircraft to attain the desired overlap. Also having complete control of gimbal angle during a mission is
Lastly, having complete control of the camera, without having to use any "auto" functions is rather important to me.

I live in flat country, so terrain awareness has never been a high priority.

@vgo195 - I have also wondered just how accurate the gps position of an aircraft flying at 20mph can really be?? When we set set gps control points and want it within a centimeter, we set up on the point for 3 minutes, staying absolutely still. So it doesn't seem possible to get an accurate position of the aircraft while its moving quickly. Yes, maybe more accurate than a non-PPK/RTK aircraft, but survey grade accuracy? No way. But if those positions, coupled with a few GCP's, give me better overall mapping, I may be willing to give it a try.

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