FAQ on the accurate geolocation pipeline

 
Note: Please note that the RTK/PPK - derived images geotags should be corrected for the lever-arms offset.

Where is this functionality implemented in the software?

  1. On the menu bar click on Process > Processing Options…
  2. Select step 1.Initial Processing
  3. Select the tab Calibration
  4. In the section Calibration, select Acurate Geolocation and Orientation as calibration method.

For more information, please refer to this article.

How much faster is the accurate pipeline?

On average, the speed increases by 20%. On larger projects, the increase in speed is up to 40%.

How accurate should my IMU be?

  • Given an IMU accuracy of 3 degrees or lower, the processing-time decreases noticeably.
  • The use of precise IMU does not improve the accuracy on the ground, e.g. at checkpoints.

As a user/drone manufacturer, what do I need in order to use the pipeline?

You need to have the RTK/PPK geotags inherent to your XMP Exif Tags

What is the type of angles I need to provide? Roll, Pitch, Yaw or Omega, Phi, Kappa?

  • We expect Roll, Pitch, Yaw angles.
  • Pix4Dmapper is capable of accounting for the residual angular misalignment (AKA boresight) provided it is constant (does not change between images) and is small (<5 degrees).

More information on how Yaw, Pitch and Roll are defined can be found here.

How could I check whether my drone correctly tags the Exif data?

Create a project and open the .p4d file and search for the following tags:

<image>

........

<accuracyXY>...</accuracyXY>
<accuracyZ>...</accuracyZ>
<accuracyOri yaw="..." pitch="..." roll="..."/>

.........

</image>

The values you see should match what you expect (e.g. with an RTK/PPK you may expect 10 cm accuracy, so you should see 0.1 in accuracy XY). The same applies for the IMU accuracy.

Note that the accuracy values represent the sigma of the normal distribution (67% of the values are within +/- 1-sigma and 99.5% fall in +/- 3-sigma), so check with the manufacturer to know what is the accuracy they sell you.

What are the default IMU accuracy values?

In absense of IMU accuracy data in the Exif data (example: DJI Phantom 4 Pro), Pix4D sets default values of 10, 10, 15 deg (Roll,Pitch,Yaw).

What happens if my IMU accuracy values are too confident or too pessimistic with respect to real values (e.g. my roll angle is 2 deg accurate but there is 0.1 deg or 10 deg in the Exif)?

  • The accuracy values need to be realistic.
  • Non-realistic standard deviations of the angles may negatively affect the processing quality in all calibration pipelines! Although the effect on the standard pipeline is negligible, over confident IMU accuracy tags may affect the processing.

Do I need to have an RTK/PPK drone in order to use this pipeline?

Ideally yes, but it is not necessary in all cases. We have seen that this pipeline helps even with less accurate drones, thermal projects...

 

 

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4 comments

  • Giorgi Lebanidze

    Hello. I used Sequoia multi-spectral sensor with Sunshine sensor (which has IMU incorporated) for my project. I wonder if the accuracy level of the images is sufficient to apply "Acurate Geolocation and Orientation" in the Calibration (step 1).

    Could anyone advice me?

    Thank you.

  • Kapil (Pix4D)

    Hi Giorgi, 

    Accurate Geolocation and Orientation is recommended for the project with very accurate image geolocation and orientation. So, I wouldn't recommend using it for the sequoia camera. In the case of the multispectral sensor, I would highly recommend you to use Alternative Calibration because it is best suited for the low texture content and relatively flat terrain, fields for example.

  • Anderson Santana

    Hello

    My project is 6000 photos (Nadir), 1100 HA area, and almost flat terrain.
    Why can't I use Accurate Geolocation and Orientation in my project?
    What can I do to use it?

  • Teodora (Pix4D)

    Hi,

    The Accurate Geolocation and Orientation calibration method is intended for images that have very precise geolocation information (e.g. RTK or PPK drones). Usually, the geotags provided by these surveyor grade drones contain image geolocation with an accuracy of few centimeters.
    The option can only be selected when you have both coordinates and angles (omega, phi, kappa) for each image and you are confident that they are precise. If these are not accurate, the calibration will fail in the majority of cases. 

    Cheers,

    Teodora

     

     

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