Doming and the DD's dropping of 3D mapping for DJI P3's


#1

Anyone who tries to make large maps using Drone Deploy with a DJI phantom will find beyond around a hectare, that the elevation image will have an unacceptable ‘doming effect’ on the image, that the centre of the map can be up to 2-3 metres higher than the periphery. This is a well known issue, based around issues of lens asymmetry, and cannot be easily corrected. The solution is to take oblique photographs as well and DD had a useful feature until late last year, where the drone would circle and take obliques at the end of the survey.

Alas DD have now dropped this is their latest release, with something called 3-D beta. I am sure it may be better, but we cannot try it, as this feature is inexplicably turned off for all the DJI Phantom 3 drones. This means that DD is now practically useless for all serious users of P3 drones, who want to generate DTM’s and .las images.

It is very simple change please can you reinstate the circular oblique function - it worked well (PS I was filming with Discovery Week, and it was deeply embarrassing that I was unable to produce the promised map)

Mark Horton


#2

I still fly my P3 Pro and haven’t seen any of this “doming” you speak of, but I’ll keep an eye out for it. As for the circular oblique function, I tried that once and the camera was pointed level with the horizon and, from what I recall, I wasn’t able to change that. I do like the idea of the feature, and the one for taking obliques around the outside edges of a rectangular shape as well.


#3

Hi Mark & Marc!

I’m curious to know if by “doming”, you are referring to the “bowling effect”? The bowling effect is a photogrammetric issue that typically affects the elevation map. Unfortunately, the only known workaround for it at this time is to capture oblique images and add them to your existing map. We’ve noticed that adding obliques can help reduce the likelihood of the bowling effect.

We replaced “Orbit at End of Mission” with our 3D Mode, which is designed specifically to generate crisper, more detailed 3D models. We understand that it’s only available for newer DJI drones, but you should still be able to capture oblique images manually or with DJI’s POI mode. You can always add these additional oblique images to your dataset to offset the bowling effect and/or to improve your 3D model. These are two great alternatives for those flying with the P3 series!

Best,
Stephanie


#4

The only time I have experienced “doming” is when the units were incorrect thus the scale of the elevation change was exaggerated. That being said, we use GCP’s on every mission so elevations are spot on.


#5

Thank you Stephanie for the response. Yes doming = bowling. Oblique photography is a workaround, and your obit at the end of mission neatly mostly resolved it. So we were very disappointed when it got dropped in your latest release - and the alternative isn’t available for P3 drones - where there are thousands of us out there using P3’s - and will be doing so into the future as its the only affordable and compact drone where we can change cameras for multi spectral use.

The trouble with your suggestions are 1) to do it manually over a large area is practically impossible and very time consuming (as the effect is on large area survey this IS a problem) 2) POI works for small areas, not the 1km + square areas that we are doing 3) Critically it requires landing the drone, swapping to DJI Go and relaunching. This means extra flight time, more batteries and possible changes in light conditions (here in the UK cloud cover moves fast). Some of our large surveys use three batteries, so this is a major limiting factor.

So a plea from your loyal users - please reinstate orbit at the end of mission!

Thanks

Mark


#6

Hi Mark,

Thank you for taking the time to explain your use cases and why manual obliques or POI might not suit your mapping needs. I understand your frustrations but unfortunately, we currently do not have plans to restore “Orbit at End of Mission”. We discontinued the orbiting feature because it was not performing reliably for all drone models and it had known issues with the DroneDeploy app. I’m sorry for the inconvenience. I will be sure to communicate your feedback to our Product team for future consideration.

Best,
Stephanie


#7

If you know what angles to take your pictures from shooting the proper isometric images is not very time consuming at all. Try strafing in addition to orbiting. Do multiple POI missions evenly spaced across the projects. While others may not recommend it I never need to land the bird when swapping from DD to DJI Go or Litchi. if your settings are correct it won’t do any but hover.

Can you provide a link to such a project or even share some of the images? I am interested to process them a couple of different ways to isolate the issue.


#9

I experienced this several times when I was flying the Phantom 3 Pro. An extra flight with low overlaps at an altitude of 300 ft or more stopped it. Crosshatch flights also work, but are much more time consuming. The second flight method seemed to be much more efficient.


#11

The “doming/bowling” elevation error can be associated with an accumulation of lens calibration errors during the SfM workflow - especially when traditional (linear/parallel) flight lines are used. Adding oblique images at various altitudes is recommended as a workaround, especially when the oblique photos are taken using gently curved, convergent, non-traditional (non-linear/non-parallel) flight lines.
Google “Gently Curved, Convergent, Non-traditional Drone Flight Paths”. The technique works for small and large areas as well as for long narrow corridors.


#12

This works unless you’re using gcps. Gcp’s plus obliques equals bad idea.