Workflow to process the Photography of "PHANTOM 4 RTK"

[BobvdMeij]

Following this as we may be getting a demo model soon and we are eager to learn more about the exact processing methodology in Photoscan!

[ruyi7952]

You can use the Inertial Explorer 8.70 or  GrafNet 8.70 post-processing software to do PPP or PPK calculations as POS.

[rmowbs]

DJI recommend to change the accuracy of the camera location to 0.1m. I have just processed your images with these setting and got these results. Just waiting for the delivery of my P4RTK. Looks promising, but would need some check points for true accuracy.

[Alexey Pasumansky]

In the latest pre-release of the version 1.5.0 (build 7205) we have added the support for the GPS accuracy tags load from XMP meta data to the Reference pane (corresponding flag should be enabled in the Advanced preferences tab).

[BobvdMeij]

In the latest pre-release of the version 1.5.0 (build 7205) we have added the support for the GPS accuracy tags load from XMP meta data to the Reference pane (corresponding flag should be enabled in the Advanced preferences tab).

That's absolutely great to hear, superb and quick handling by the dev team! Will it also be able to handle/import the camera calibration data?

More importantly however, at least for us, when will users of Agisoft Photogrammetric Kit be able to utilize this functionality? We have already been waiting for the first build of Metashape for over six weeks, let alone how much longer build 7205 will take..

[BobvdMeij]

Is anyone, perhaps, capable of clarifying the values encircled in green in the attachment? It depicts three seperate metadata/XMP files extracted from three different Phantom 4 RTK's.

The values in blue most certainly relate to the various interior parameters that were distilled during the a priory camera calibration procedure seemingly conducted by DJI. The latter five likely embody radial (k1-k3) and tangential (p1-p2) coefficients, but I'm not entirely sure. The same goes for the first series of values; they may be related to the focal length or principal point coordinates (cy, cy), but they seem to be expressed in a different unit compared to how they ought to be inputted in Photoscan's camera calibration dialog. As I'm eager to import these parameters as fixed I really need to know what the values exactly represent, any help is much appreciated!

Ps. The middle example doesn't contain any camera calibration parameters. This was likely due to the option 'Distortion Correction' being activated in the DJI app which causes the calibration parameters to be omitted.

[Paulo]

Hi,

yes I think you are right, the last 5 correspond to k1,k2,k3 and p1, p2 distorsion parameters... the 3rd and 4 th parameters seem to correspond to Principal point position in pixels. In screen capture, I show calibration done on P4RTK set corresponding to first example. In this case no dewarp parameters were applied and camera exhibits high radial distorsion… In this calibration, I have also a r4 radial parameter estimated....The first 2 parameters are more difficult to explain, they seem to correspond to something like focal length in pixels ( 2 values for affinity^?) but are far from 3663 value estimated in PS.... DJI should give more information on this especially since it puts in EXIF calibrated focal and PP at:
Calibrated Focal Length         : 3666.666504
Calibrated Optical Center X     : 2736.000000
Calibrated Optical Center Y     : 1824.000000

[BobvdMeij]

Hi,

yes I think you are right, the last 5 correspond to k1,k2,k3 and p1, p2 distorsion parameters... the 3rd and 4 th parameters seem to correspond to Principal point position in pixels. In screen capture, I show calibration done on P4RTK set corresponding to first example. In this case no dewarp parameters were applied and camera exhibits high radial distorsion… In this calibration, I have also a r4 radial parameter estimated....The first 2 parameters are more difficult to explain, they seem to correspond to something like focal length in pixels ( 2 values for affinity^?) but are far from 3663 value estimated in PS.... DJI should give more information on this especially since it puts in EXIF calibrated focal and PP at:
Calibrated Focal Length         : 3666.666504
Calibrated Optical Center X     : 2736.000000
Calibrated Optical Center Y     : 1824.000000

High Paulo,

Not exactly sure what you mean but do you mean that you processed your data letting Photoscan estimate/optimize all camera parameters, OR did you import the values provided by DJI as fixed parameters?

In the meantime I've received official word from DJI on the meaning of the nine consecutive values in the DeWarpData field:

Code: [Select]

calibrate_date;fx,fy,cx,cy,k1,k2,p1,p2,k3
Where fx;fy is the focal length in the pixe and where cx;cy is the optical center expressed in pixel coordinate (Origin point as the center of the imager).

Now that leaves me wondering what settings we should use in Photoscan's camera calibration dialog as there's only one field for focal length, whereas the XMP metadata provides us with two (horizontally and vertically). I also reckon we should go via the Convert Calibration setting (within the Camera Calibration pane) and change the value in the Type-field, which is set to Photomodeller by default, to Pix4D Perspective. This would be due to Photomodeller expressing both focal length and principal points in millimeters (mm), whereas the P4RTK's XMP metadata expresses these values in pixel (pix) units and this is allowed when changing the Type-field within Convert Calibration to Pix4D Perspective.

Again I'm not sure and still guessing on some details, it'd be great of some of the developers could tune in to this!

[Paulo]

BobvdMeij ,

thanks for the update… makes more sense now...

Yes I did a new calibration in PS without entering Dewarp Data parameters...

However the big difference between fx and fy (affinity) is not reflected in the PS adjustment as b1 is very small.....

By the way in PS calibration f = fy and b1 = fx-fy

My only doubt is p1, p2 parameters as in Pix4D they are inverted wrt PS... so maybe support can confirm how to treat p1, p2 from DJI Dewarp parameters for use in PS ….

[Domingo]

Hello
Attached 4 photographs of information provided by the DJI technical service.

[Domingo]

I had problems uploading the photographs.
Attachment 2 more.
Greetings.

[takahiro]

Nice to meet you, everyone.

As Dragline says, accuracy is poor if you do not capture the last 8 digits of the coordinates.
In the build 7205, meaning that you added the reading of the GPS accuracy tag is lost.
Thank you.

[takahiro]

Postscript.
Paste the image link for reference.
(It is where you highlight the text blue.)

Thank you.

https://drive.google.com/file/d/10hATO3k08TcW7W0TnwbkD_9G99QhxP2_/view?usp=sharing

[Eirik Strøm Pedersen]

Hey everyone.

As i understand it you recommend to turn of the Distortion Correction in the DJI Flight Software? And then do a manual calibration where you import the .mrk file into Metashape?

[smcmurray]

Hi there we are currently trying to process some P4 Pro RTK data through Agisoft but we are having some issues getting it to read in the accuracies from the metadata - can anyone that has it working please share their workflow ? @Alexey Pasumansky is this working in 1.5.0 release ?


Any help is appreciated

Regards
Steve McMurray