PPK without ground control points

I’m still learning with the ppk process. I’m using phantom 4 pro. and equipped with tally antenna and reach m+

has anyone tried a large area without GCP and get high accuracy for the flights?
also wondering what’s the best settings for pix4dcapture to fly grid in scenario?
has anyone got report with GCP tied up with PPK processed and procedures to compare?

is there any other method to improve accuracy without ground work?


Hi, we use Ph4 pro with reach m+ and make 10-15 square km without GCPs per day.
Accuracy is 5-6 cm.
Flight velocity is 10 ms, Altitude is 150-170 meters.

hey van,

do you have any processing or procedures you can share?
if you do have could you send me an email?

how do you fly and process?
so no GCP or no ground work at all?

thank you

Those are tight specs for mapping. The most consistent setup is 18mph at 260ft which creates about a 75% overlap.

Do you mean frontal overlap because of the image frequency? I think Metashape recommends 80/60% frontal/side overlap. I would go for more than 65% side overlap.

I think it would be a miracle if flying at 170m and 10m/s with a Phantom can result in an accuracy higher than 2 px. I would be very interested to see examples.

If you want to map with a Phantom I would have a look at the Ashot solution.

If you work with LEDs and photoresistors: have you found my timemark time machine?

Those flight numbers come from many flights using Litchi with both a Yuneec H520 and a P4P. Flying lower produces better resolution, but does not necessarily mean it is a more accurate map. The higher you fly the more tie-points you get and the better that the stitching is. You just have to get your overlaps dialed in. For efficiency sake 75 front and 65 side may be at the lower end, but it also allows me to fly most of my sights with one battery.

hey i’m curious about your setup as you said
could you please give me more details?
i have setup reach M+ tally antenna on my phantom.
thank you

Hi, we use Ph4 pro with reach m+ and make 10-15 square km without GCPs per day.
Accuracy is 5-6 cm.
Flight velocity is 10 ms, Altitude is 150-170 meters.

Michael, off topic but how do trig regular spaced pictures between 2 Litchi waypoints ?

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We use Ph4pro and AShot.cc to synchronise Shutter and Reach M+.

Talisman antenna is very bad for UAV, because it needs ground plane.

For best GNSS signal you may use this spiral antenna:


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you may use interval shooting. This setting is in camera settings.
Interval can be 2 or 3 or 5 seconds.

Given the lack of groundplane (or rather, a very small groundplane), how does your suggestion cope with multipath coming from the ground?

You may ask this question to Antenna Factory.
I dion’t produce antennas.

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When you plan on the web browser it gives you a distance. I typically stay at 100 to 110 ft. I’m not sure if the app gives you the distance or not. The only thing you have to do from there is calculate your speed to work with a 2 second interval image capture.

I guess that mean you could also do raw?

Helical antennas are omnidirectional, so the UAV can be tilted due to velocity or wind and it does not affect the incoming signal. Not having a ground plane might be a disadvantage in that you can’t eliminate reflected signals bouncing back up from the earth, but the problem associated with that should decrease with altitude.

I think you gain something and you loose something by going with a helical antenna, but it is probably not a bad choice. Maybe another user here has done some comparison tests and can chime in with an opinion.

Well, usually they are 180 degree or narrower, depending on the number of turns. The are also natively circular polarised (GNSS is RHCP), so that will mitigate some of the multipathing). Would be interesting to do a side by side comparison… Free idea for someone with an M+, right there !

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Yessir. That is one of the handful of reasons why I fly sometimes with Litchi over DroneDeploy. Not very often though.

Many of the companies offering survey drones use helix antennas. E.g. eBee. Groundplans improve the result but they are less necessary than with patch antennas.

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I would think being in the air would reduce multi-path? If your mask is greater than zero then there shouldn’t be any problems as compared to ground use.


To The most extent, yes. But there will be multipath signals from sats above the horizon, hitting the ground and bouncing back up. Most of these should be attenuated by the fact that hitting the ground reverses the polarity and makes the signal LHCP, but antennas aren’t perfect in that regard either.
In any case, a ground plane would take care of this completely, but has obvious disadvantages on a UAV. So if the helix is “good enough” (which I think it is), then no big problem.

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