How to import image location accuracy

RE: How to import image location accuracy

Oto — Fri, 03 May 2019 03:52:11 GMT

I have tried RTK dataset it works well but got strange results regarding altitude. Contextcapture has fisheye lens setting which you could try.

But if it is so that if using JPG the DJI already uses some fancy barrel distortion removal then it could explain why even if using precalibration I still sometimes get curved model. Will try to check with RAW/DNG format how it looks then.

RE: How to import image location accuracy

Caleb Baildon — Thu, 02 May 2019 21:10:40 GMT

Hi Oto. I'm not an expert on the technical difference between fisheye and rectilinear. But this thread makes it clear that corrections are made onboard the drone to make images with nice straight lines https://forum.dji.com/thread-83571-1-1.html.

Have you used the Phantom 4 RTK?

I can tell you as a fact that you have a choice in images it will output - With or without 'distortion correction'.

When using 'with distortion correction' the camera lens parameters for the Phantom 4 Pro work. Pix4D classifies this as a 'rectilinear lens'. With this setting straight lines look nice and straight.

When using 'without distortion correction' the camera lens parameters for the Phantom 4 RTK work.Pix4D classifies this as a 'fisheye lens'. With this setting straight lines look warped near the photo edges, just like the Phantom 2. Pix4D also classified the P2 lens as fisheye.

I don't know if Pix4D is using the correct terminology or not, all I know is what works and what doesn't.

Nothing to do with rolling shutter.

RE: How to import image location accuracy

Oto — Thu, 02 May 2019 19:51:44 GMT

P4 doesn't have fisheye lens it has 94° FOV wide angle lens. I am not aware of any corrections applied by P4 for barrel distortion in firmware. Maybe you are confusing with rolling shutter eefeff? Yes Pix4D has rolling shutter adjustment but it doesn't actually give better results.

RE: How to import image location accuracy

Caleb Baildon — Wed, 01 May 2019 20:21:12 GMT

All DJI Phantoms have fisheye lenses, but since the Phantom 3 the images are corrected for this on the fly, so the images you download from the drone do not have the barrel distortion (ie horizons are straight). However with the Phantom 4 RTK it now give the option to have the photos with out this correction applied to improve the accuracy of the processing. The camera in the Phantom 4 RTK is identical to the Phantom 4 Pro, but in Pix4D they have different calibration parameters. The RTK camera (without 'distortion correction' turned on) is a fisheye lens, and the Phantom 4 Pro is a rectilinear lens. However, it you use the RTK with the 'distortion correction' turn on, then choosing the calibration file for the Phantom 4 Pro in Pix4D works just fine.

I get what you mean about undistorted images not having camera parameters, but that just means they don't have real phyisical lens parameters, they can still have calculated/psuedo parameters, as they have for Phantom 3 and 4 cameras.

I hope Bentley have added support for the Phantom 4 RTK camera to Context Capture update 12.

RE: How to import image location accuracy

Oto — Tue, 26 Mar 2019 07:06:11 GMT

[quote userid="633520" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/177107/how-to-import-image-location-accuracy"]As a side issue version 4.4.11.60 does not recognise the camera parameters for the 'undistorted' images from the DJI Phantom 4 RTK[/quote]

What do you mean by this? Undistorted images are flat so there are no camera parameters anymore.

RE: How to import image location accuracy

Oto — Tue, 26 Mar 2019 06:58:34 GMT

>So for these jobs I could do the AT in Pix4D, and then export the camera positions to CC

It is of no use as CC calculates camera positions differently you won't get any improvements. But yes CC gives more accurate results just requires good input photos without out of focus photos and photos without rolling shutter distortions.

Regarding P4 RTK there is still not clear how the altitude values are used - https://communities.bentley.com/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/176371/dji-phantom-4-rtk-ntrip-processing/511214#511214

RE: How to import image location accuracy

Caleb Baildon — Mon, 25 Mar 2019 17:12:49 GMT

Thanks Oto. That was my suspicion. I guess CC intends for all images in a Block to have the same accuracy and if mixing accuracies of groups of images to AT in different in Blocks and then merge.

The reason I use CC over Pix4D, is for the quality of the meshes, particularly for complex objects. So for these jobs I could do the AT in Pix4D, and then export the camera positions to CC. I will add the assigning of accuracy to individual images to the wish list.

RE: How to import image location accuracy

Oto — Mon, 25 Mar 2019 07:31:01 GMT

It seems CC doesn't have such option. There is only global aerotriangulation option to use accurate or inaccurate positions. Also there is option to only adjust positions using tolerance where you could input maximum range but have not noticed that it gives any better results.