That's amazing. What is your vertical repeatability at 20 miles?
Here in New York State at 20 miles from a BASE, my vertical will be ?ñ0.2ft
@leegreen typically I see less than ?ñ0.08~ish, often much better.?ÿ Good enough for this dumb dirt sirveyur.
We will see up to a tenth of variation in the same session, but we will see easily two to three tenths difference when returning to the same points only a few hours later. This is with a network, not single-base solution, and pretty much anywhere within the coverage area.
Even around here with a well-run RTN and plenty of stations around running full GNSS, this is just how it is. If I want repeatable vertical with respect to the network, we're doing multiple 1- to 2-minute observations spaced out over a few hours.
Then again, for local project control that only need to be tight within itself, a single visit will suffice to bring us within tolerance, and then we can tighten things up with TS and level work. Most surveyors claim that sub-tenth accuracy because they only observe with GNSS once, at the same time of day, and never again.
There is no such thing as a VRS base "five miles away" as far as I know. That is why I was asking...I was trying to fill in my ignorance. The software creates a Virtual Reference Station at the location that you start your session. So, as far as I know there is no reason to ever have a base very far away at all. Depends on what you mean by "base", I suppose.
@dmyhill?ÿ ?ÿI thought that was the whole point of a VRS? Like having a single base line station right on your site.
@leegreen?ÿ - is it not easier to just use the aerial GCP's you set and log their locations in with either GNSS or a total station if the site is smaller to mid size and just do some random spot checks for the topo on the asphalt, dirt and grassed areas? seems like survey grade equipment would work better anyway than DJI's stuff plus the drone is constantly moving & drifting I would think. I don't have any personal experience so that's why I ask
@dmyhill?ÿ
Correct. The VRS creates a virtual base at your initialization point. However. if you reset your VRS, what is the repeatability of your position when the Network CORS is more than 5 miles away?
When you return to a site the next time, can you use the same VRS initial point??ÿ
Yes, using the correct amount of GCP's will be just as accurate as PPK or RTK drone. The DJI P4 Pro and DJI P4RTK have the same camera, so yes same results once registered correctly. With PPK and RTK you still want several GCP's or checkpoints for ground-truthing.
@leegreen - thank you sir for the clarification! curious how your results for topographic work come out? I would think that the density of the point cloud would help tremendously as compared to conventional methods
Where there is very little texture in the surface over a large area then the PPK/RTK will reduce the risk of a photogram mismatch causing a shift on a number of overlaps, so you don't need to intensify the density of GCP in those areas. The texture problem is exacerbated in poor light (when you shouldn't be flying - but occasionally needs must!).
@mark-o?ÿ
I do not know. They typically have a free demo period with each receiver.
We've recently been wondering the same thing (using a standard base, i.e. leica/trimble) to then post process flights. The goal being to have all photos geotagged with PPK coordinates adjusted using the on-site base, prior to then doing our regular mosiac process.
I came across this recently and it appears to be the best solution (though I have not used it):
https://geocue.com/asp-for-dji-p4-rtk/
https://support.geocue.com/wp-content/uploads/2019/04/ASPSuite_User_Guide-V10.pdf
