How to calibrate the DJI Zenmuse P1

Recently, we have received a number of requests on how to calibrate the DJI Zenmuse P1 camera, since they are no longer calibrated from factory (due to the additional lens options now being available). We have compiled a guide, based on the DJI P1 operations guidebook.

Camera calibration

Camera calibration (also known as camera resectioning) is the process of estimating intrinsic and/or extrinsic parameters. Intrinsic parameters deal with the camera’s internal characteristics, such as, its focal length, skew, distortion, and image centre.

For DJI Phantom 4 RTK: Each Phantom 4 RTK camera goes through a calibration process that measures the distortions of the lens, and records the corresponding undistort parameters in XMP DewarpData. This DewarpData will be used by DJI Terra in the aerial triangulation process.

However, the Zenmuse P1 camera doesn’t go through this factory calibration process when it is produced, because of its detachable lens design. When you purchase a new P1, it is recommended to calibrate the camera following the below procedure. Each time when you detach and attach the lens, please also calibrate the camera parameters again.

Collecting calibration data

1. Look for a measurement area for the calibration, preferably locations with greater altitude difference such as a building or hillside.
2. Set check points so the quality of the calibration results can be checked (non-essential).
3. Create measurement areas using smart oblique mission planning or oblique photography (for five flight paths).
   Parameter requirements: To collect more than 100 images, with an fore-and-aft and horizontal overlap rate of at least 80% and 70% respectively, where no less than 2/3 should be oblique images. No requirements on flight altitude.
4. Turn on RTK and once it enters the RTK Fix mode, launch the aircraft.

Modeling

Using DJI Terra v2.3.1 or above, create a new 3D reconstruction mission and start modeling;

Calibration

1. After modeling is completed, open the mission folder, find the sfm_report.json file under the AT-report directory and copy it onto the camera’s SD card;
2. Plug the SD card into the P1 camera, link it to the aircraft and turn on the power. The calibrated intrinsic parameters will be written into the camera automatically.

Testing

Capture an image, open it in Notepad, and search for the XMP data. If DewarpData field can be found, it means the camera’s intrinsic parameters have been calibrated successfully.