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Processing DJI Phantom 4 RTK datasets with Pix4D

Hi Guillermo,

Pix4Dmapper reads information from the image EXIF data. It reads both standard EXIF tags and Pix4D defined camera XMP tags.

In the XMP tags, you will find the orientation and accuracy-related information written in the parameters Xmp.Camera.Yaw, Xmp.Camera.Pitch, Xmp.Camera.Roll, Xmp.Camera.GPSXYAccuracy and Xmp.Camera.GPSZAccuracy: Specifications of xmp.camera tags.

To make sure your images contain such information, you can use this tool by dragging and dropping one sample image and looking for the necessary parameters: metapicz.

Cheers,
Teodora

Thanx for reply. I did what you said, and the images has the information. So, i dont understand why pix4d is not reading it

Hello again,

Indeed, the accuracy values are in the metadata. Have you also tried processing the project with the calibration method Accurate Geolocation and Orientation? I think the software should be able to pick up the accuracy of the geotags. More details can be found here: FAQ on the accurate geolocation pipeline.

Cheers,
Teodora

I cannot select that option

image

Hi,

This means that the images do not have accurate geotags. Do you have a sample of the image geolocation file? The values should indicate very accurate geolocation and orientation, as shown in the screenshot below:

Cheers,
Teodora

Hello,
I am having similar issues, where Pix4D is shifting the images irrespective of the high-accuracy PPK geolocaiton through PropellerAero.

We are working in an Australia co-ordinate system (GDA94) and an Australian Geoid grid (AHD09). The input file is already converted to the co-ordinate system and the geoid. I select the co-ordinate system we are using (GDA 94 MGA Zone 54), and currently select “Arbitrary” as the vertical geolocation.

I find that these settings are producing poor accuracy compared to the cloud processing through PropellerAero. The reason we are not cloud processing is that we want to be able to crop the data and edit the point cloud, but data accuracy takes precidence.

The data MUST be in the aforementioned coordinate systems to meet our clients requirements. What settings do you recommend in Pix4D to achieve the proper map accuracies from PPK?

Hi Daniel,

The processing workflow for RTK should be similar to PPK. In the end, you are dealing with image datasets that have highly accurate geotags, only their origin differs.

If you are getting some shifts, I would suggest first double-checking the PPK correction process and make sure the appropriate data was chosen:

  • the rover file (rinex data from the drone) - ensure there was no strong wind that induced vibrations to your drone.
  • the base station file (rinex data from a fixed base station) - this should be as close to your study area as possible.
  • broadcast ephemeris data (precise satellite navigation data) - this acounts for orbital errors and should be reliable.

The last resort would be to correct the shift by including GCPs in the project. RTK/PPK geotags in consumer drones is a relatively new technology and the workflows for using them have not yet been clearly defined in the industry. To what extent they can replace GCPs as a means for high accuracy in mapping is not thoroughly understood. In general, the best practices would still require the use of GCPs and checkpoints to meet proven absolute accuracy standards.

However, the benefit of RTK/PPK image geotags is that you can reduce the number of GCPs collected for a given project.

Hopefully this makes sense.

Best,
Teodora

Hi Teodora,
Thanks, could you please clarify a couple of points though:

  1. is there a way to import the co-ordinates and their accuracies, but not the camera orientation? So far, I can only find a way to import co-ordinates
  2. If I am importing the PPK data in a local co-ordinate system and a geoid, will that effect the accuracy of the processing?

Thank you

@Daniel_Ierodiaconou,

  1. In order to import image geolocation with the accuracy values, the orientation angles need to be determined in the file as well. If the orientation angles are written in the EXIF of the images you can create a project in Pix4Dmapper and use the To File… option to export them in a text file. Then include the exported omega, phi, kappa angles in file with PPK geotags and use the From File… to import everything.

  2. If your final goal is to deliver accurate results based on the already transformed values of image geotags then I would recommend changing the vertical coordinate system to Arbitrary in the image geolocation and outputs coordinate system menu. This way no transformations will be done during processing and results will be in the same reference frame as PPK geotags.

Let us know how it goes,