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DJI Phantom 3 4k - custom camera parameters

Hey All,

I am flying with DJI phantom 3 Professional. It has the 4K camera on it. In the setup process for PIX4D it has a phantom 3 camera listed. After a flight and comparing survey data with RTK shots taken with a rover it’s shown in accurate. I adjusted camera settings on PIX4D capture program on my computer after hours of research online trying to find proper Focal Length etc. I was able to get it close. Wondering If anyone has created a custom camera setting for DJI 3 professional and seen accurate results? 

I had GPC measured with RTK set up with in the pictures and used in processing. 

Hi Adam,

In our database, we do have the Phantom3_Professional_video_4K_0.0_4096x2160. In case this is not the same camera as you have then you will have to further proceed with a camera calibration as per the instructions that are given here: How to calibrate a Perspective Lens Camera.

To better understand the current accuracy of your project I would need to take a look at the quality report. Could you post it here?

Thanks,

Ina

Hey Ina, 

So the reason we started using a customized camera is because we kept getting optimized errors anywhere from 3%-16% with the default DJI phantom 3 camera. We’ve tried going back to default camera settings and see the same issue.

It’s seems as the slopes and high vertical changes are troublesome. 

We add some of the RTK info as control pts. and leave some as check pts. The control points always hit but veer off between pts and check pts. miss. 

I usually collect the data and have help processing back at the office. So I will have to consult with them for more input on “how RTK info is added”. 

Ina, 

I will also try get the quality report posted. 

 

Thanks!

@A Stanger, you will receive a direct message shortly so that you can more easily share a copy of your project’s latest Quality Report.

@Anyone following along, do not hesitate to let us know if you have any questions in the meantime.

This is a portion of the site. We broke the site into smaller flights and increased ground control coverage to see if we could get better accuracy. 

If you have access to the cloud servers all of projects has been uploaded and processed there. 

There were some previous “rubble pile” project uploads where we had modified our camera parameters and found success on a lot smaller project size. 

To answer a couple of the initial questions:

I believe the camera is the stock 4k camera that came with the Phantom3 professional. Although we inherited it from another department in the company and are unable to locate any of the manuals or information that came with it upon purchase to verify that.

There was no RTK or PPK applied to the flight data. We use an RTK Trimble rover and base setup to obtain our GCP coordinates that are ultimately imported into Pix.

We did notice that when importing the pictures into Pix it reads the EXIF data and applies the P3P camera to the project. We saw a discrepancy where the P3P default focal length is 3.61 mm in pix but in the image properties it is 4mm. When we customize the camera to 4mm in Pix the report shows that the camera optimization is within acceptable values but the georeferencing is out of tolerance. When we leave the camera settings as default the values are shown as in the attached report. In both cases the generated point cloud is inaccurate.

Hi Adam, thank you for letting us know about your projects on Pix4D Cloud.

  1. I do not have any reason to believe that the department that previously owned your drone made any meaningful changes to your camera that would affect your project’s results.

  2. Thank you for confirming that you used your RTK Trimble rover to collect your ground control points.

  3. Each copy of Pix4D Desktop includes a database of camera models that Pix4D manages on an ongoing basis. The internal camera model database contains a single camera record for each camera model. Knowing that no two cameras are identical, each record in the internal camera model database is an approximation of all units of that camera model.

Pix4D’s image processing engine takes the Initial Camera Model as an input and then solves for the Optimized Camera Model each time you process a project for two reasons:

A. We do not know your camera’s internal geometries accurately enough based on the information that is available in the images’ metadata
B. Your camera’s internals can change enough over time that we do not want to automatically apply internal geometries that you solved for previously as input in another project.

Pix4D Desktop automatically applies 3.61 mm as your camera’s initial focal length because we found that it was more representative of a typical Phantom 3 Professional camera than 4 mm, which the images’ metadata and technical specifications documentation references. However, not all cameras are identical, so it is possible that your camera’s internals deviate by more than 5% from the camera model in Pix4D’s internal camera model database.

You may have noticed that Pix4D’s image processing engine arrived at 4.1 mm for your camera’s optimized focal length in your latest iteration of East Flight, which is closer to what DJI’s technical specification mentions. However, we must find a balance between the optimized values that Pix4D’s image processing engine solves for your camera’s internals and your ground control points so we cannot solely on the percent difference between your camera’s initial and optimized internal parameters to determine the quality of your project.

  1. I have reason to believe that excessive amounts of linear rolling shutter distortion in your images are the primary source of error in your latest reconstructions. Tests we conducted with your _East Flight _project yielded significantly better results when Pix4D’s image processing engine optimized for linear rolling shutter distortion. Please verify that you acquire similar results by enabling Linear Rolling Shutter Optimization and processing Step 1 again.

You may receive a warning in the Quality Check table highlighting that there is a significant difference between the project’s Initial and Optimized Internal Camera Model Parameters, but you can definitively verify that your results are accurate by incorporating a set of checkpoints before processing Step 2 and Step 3.

  1. For future projects, you can estimate whether your proposed mission is susceptible to significant amounts of linear rolling shutter distortion with Pix4D’s basic Vertical pixel displacement calculator. For your reference, we have estimated that DJI’s Phantom 3 Professional camera has a rolling shutter readout time of approximately 33 milliseconds.

Do not hesitate to let me know if you have any questions.