Hello all,

I have a question regarding using my Mavic 3E RTK drone to do oblique mapping of forested plots in an area where I cannot receive corrections.

My workflow is:

- Set up 1 emlid reach RS2 in open-sky to log its position for 6+ hours

-Travel to my sites (1-10km away) and collect drone imagery using a Mavic 3E with the RTK module.

-Use PPP to correct the base stations position, then PPK the resulting drone imagery with the updated base station position.

My question is,

I have a second emlid reach RS2 available, would it be worth it to bring it with me to the plots and set up on an unknown point to send RTK corrections to the drone?

Or just fly the drone with the RTK module without setting up another reach unit at my plot locations?

I am wondering if it may affect the PPK process if the drone images were corrected with an RTK from an unknown point during the flight, even if I process them using the known base station position later?

Thank you all for any insights into this!
edit: I should add that I need both absolute and relative accuracy for this project.

If you have internet at both locations you could use Emlid Caster to send your corrections from the original RS2 1-10km away. This would provide you with relative accuracy. Then once you have your corrected base station position you'll apply that correction to end up with absolute accuracy. If you use one or two RS2's it doesn't matter you'll still end up with only relative accuracy.

Johnnokomis Posted at 5-2 14:00
If you have internet at both locations you could use Emlid Caster to send your corrections from the original RS2 1-10km away. This would provide you with relative accuracy. Then once you have your corrected base station position you'll apply that correction to end up with absolute accuracy. If you use one or two RS2's it doesn't matter you'll still end up with only relative accuracy.

Unfortunately I do not have internet at either location.

Which is why I will have to ultimately use ppk with the corrected base station coordinates.

But wondering if it is worth doing RTK anyways with another reach close to the drone, or just let it fly with the RTK module by itself and collecting gps data to ppk afterwards.


I.e would using RTK at the plot location (without a know coordinate) provide any increased accuracy with ppk being done afterwards anyways?

bengwill Posted at 5-2 14:13
Unfortunately I do not have internet at either location.

Which is why I will have to ultimately use ppk with the corrected base station coordinates.

There's nothing wrong with the way you're currently doing it which is PPK only. If your end goal is to have global accuracy then I don't see much of an advantage with flying while receiving incorrect corrections. Especially when you'll be applying your accurate corrections from a completely different base station. There's others here on the forum who have more geospatial knowledge than myself so maybe they can give a better answer. In my opinion though I'd say it would make no difference or may actually have a negative impact on your final deliverable.

In this scenario I would place my base station on a GCP which will be visible on the dataset.  While broadcasting RTCM corrections to the drone from this base (RTK).

Then at the office you will have two options, both start with PPP the base to find its exact coordinates.  Then :
1/PPK the images with this new precise coordinate in the RINEX header
or
2/process the images as they are and shift the dataset to align it with the GCP of the base. Which is faster.

3/You can try both method and see what suits you the best.

Important ! Process everything in WGS84 both horizontal and vertical, then perform transformation on the final dataset (point cloud, ortho, DSM ...)

Johnnokomis Posted at 5-2 15:43
There's nothing wrong with the way you're currently doing it which is PPK only. If your end goal is to have global accuracy then I don't see much of an advantage with flying while receiving incorrect corrections. Especially when you'll be applying your accurate corrections from a completely different base station. There's others here on the forum who have more geospatial knowledge than myself so maybe they can give a better answer. In my opinion though I'd say it would make no difference or may actually have a negative impact on your final deliverable.

Thank you for your input, these were my thoughts as well regarding the RTK with an unknown base not adding much value to the coordinates. I understand that the RTK module adds enhanced GNSS capabilities which will help with post processing.

LV_Forestry Posted at 5-2 21:17
In this scenario I would place my base station on a GCP which will be visible on the dataset.  While broadcasting RTCM corrections to the drone from this base (RTK).

Then at the office you will have two options, both start with PPP the base to find its exact coordinates.  Then :

Excellent points and I will be trying these approaches. The main challenge with this project is that I must align the photogrammetry point cloud with a point cloud captured with terrestrial LiDAR at each of the plots.
Thank you!

bengwill Posted at 5-3 05:24
Excellent points and I will be trying these approaches. The main challenge with this project is that I must align the photogrammetry point cloud with a point cloud captured with terrestrial LiDAR at each of the plots.
Thank you!

In this case I strongly urge you not to do oblique.  
Do a NADIR canopy scan, put your georeference spheres (I expected you are using that with a TLS) in places where they will be visible above the canopy.  
This is how I do it.