Metadata accuracy problem for E90 + Pix4D?

DroneCalzone · Jul 4, 2018

Hello!

have you heard about problems with metadata accuracy with the E90? The Pix4D report says that there is a relatively big difference between given camera parameters and the parameters calculated from the images themselves.

This results in weird stuff, like unnaturally concave terrain models, or overall lower precision, despite using GCPs. What hurts me the most is that a P4P gets nice, repeatable maps with better geo-accuracy .

It seems that the slower the H520 goes, the smaller the inaccuracies are. Best results are with the stop for every photo setting but this is a major pain as it takes much longer and still the results are not as good as a P4P (which took photos in continuous flight).

Any ideas how to fix this?

arruntus · Jul 4, 2018

Yes, is very easy.

Step 1, Calibration, optimization of internal parameters -> all prior.

I'm sorry I have it in another language, I think it's like that in English. You activate all prior and it already gives you the right results.

DroneCalzone · Jul 5, 2018

huh... well, I didn't expect it to be so simple!
What does this option do?

Thanks for your input!

Edb · Jul 5, 2018

Following.

We have had problems but it was related to the incorrect shutter option being used by the default Pix4D database. In the camera parameters we needed to ensure that the shutter option was set to linear rather than global or fast shutter. We then saved this setting to the database and it is saved for the future. Results are now excellent to GCP's and check points. Without the rolling shutter correction we were up to 0.5m out.

arruntus · Jul 5, 2018

I only put that parameter in once and it's already been saved. It is very important to put it in linear shutter.

RichA · Jul 9, 2018

arruntus said:
Yes, is very easy.

Step 1, Calibration, optimization of internal parameters -> all prior.

I'm sorry I have it in another language, I think it's like that in English. You activate all prior and it already gives you the right results.

Hi arruntus,
Thanks for linking me in to this discussion. I've got Pix4D set to recognize the linear/rolling shutter, but I'm not sure what you mean by your "Step 1 ..." instructions. Is this calibration of the H520 or Pix4D? (I can't do anything with my H520 now since my E90 is unresponsive.) While going through a tutorial for Pix4D they do NOT recommend saving the optimized parameters as a part of the camera parameter description - it seems that the optimized values may be project specific? If you could clear up what you meant, I'd appreciate it.

I was hoping to go out tomorrow with a survey programmed to included pauses at every photo point to see if this is necessary to get better geolocation outcomes. However, my E90/gimbal unresponsiveness may have nixed this opportunity. Effing A.

Cheers,
RichA

DroneCalzone · Jul 11, 2018

Hey guys.

I got a nice response from Pix4D directly. It corresponds with what you guys wrote, but has some more details, so I'll throw it in here:

The camera has a rolling shutter which can be an issue for the reconstruction depending on the flight conditions and the area that is mapped. To mitigate the effect, we suggest applying a specific algorithm especially for flights with a regular pattern (lines). To learn more about this issue and apply the linear rolling shutter correction, please see How to correct for the Rolling Shutter Effect.

If the results are not satisfying, you can try the following together with the linear rolling shutter algorithm:
1. On the menu bar, click Process > Processing Options...
2. Select 1. Initial Processing and then the tab Calibration.
3. Make sure the Advanced box at the bottom left corner is checked.
4. In the section Calibration, from the drop-down list for the Internal Parameters Optimization, select All Prior.
5. Click OK.
6. On the menu bar, click View > Processing.
7. On the processing bar, check 1. Initial Processing and uncheck steps 2 and 3.
8. Click Start to re-run step 1.

We also recommend flying slower and/or higher to reduce the amount of linear rolling shutter distortion that is present in the images. You can see how your camera and flight parameters influence the amount of linear rolling shutter distortion that is present in your images with Pix4D's Vertical Pixel Displacement Calculator.

Edb · Jul 11, 2018

Thanks for this.

What does the select All Prior mean? Or do?
Do we use this option every time? Or only when the point cloud looks noisy, GCP errors too large? Can it improve the accuracies of our datasets?

Thanks, Ed