Camera Optimization - PIX4Dmapper

Issue

When the quality report shows camera optimization above 5%, this can indicate an issue with a project.

Description

The focal length/affine transformation parameters are a property of the camera's sensor and optics, and these actual values can vary with temperature, shocks, altitude, or time. The calibration process starts with an initial camera model and optimizes the parameters used to model the camera in Pix4D to produce more accurate results.

Indicators:

Review the initial checks section of the quality report as shown below.

• An initial camera model should be within 5% of the optimized value to ensure a fast and robust optimization.
• The percentage of the difference between the initial and optimized focal length for a perspective lens, affine transformation parameters C and F for a fisheye lens, is between 5% and 20%.
• The percentage of the difference between the initial and optimized focal length for a perspective lens, affine transformation parameters C and F for a fisheye lens, is more than 20%.

Causes

Several causes can lead to this issue:

1. Flat and homogenous areas do not provide enough visual information for optimal camera calibration.
2. The images have significant rolling shutter distortion.
3. Blurry images, a dataset with low overlap, damaged camera.
4. Wrong initial internal camera parameters. The camera has been physically modified with a lens filter or similar accessory that affects the optic.
5. Preprocessed or cropped images.

Solutions

Possible solutions to the previously listed causes are proposed below.

For cause 1:

• Process with lower Keypoints Image Scale: This processing option can lead to a higher number of calibrated images than the default original keypoint image scale. For more information: Menu Process> Processing Options... > 1. Initial Processing> General.
• Enable Geometrically Verified Matching.
• Set internal calibration parameters to All Prior in Step 1 processing options.

For cause 2:

• Calculate the Vertical Pixel Displacement and enable linear shutter optimization in the Image Properties Editor if needed.

For cause 3:

• Recapture Image Dataset.
• Check the camera for any potential damage.

For cause 4:

• Verify that the camera model defined is correct for the images used in the project.
• If the camera is not in the Pix4D database, then it may be necessary to generate these values by following the instructions:
  • Fisheye lens calibration.
  • Perspective lens calibration.

For cause 5:

• Do not modify the images before importing them into PIX4Dmapper for processing.