PIX4Dmatic provides the option for perspective camera lens calibration through the internal camera parameters window, optimizing camera performance for accurate photogrammetry. This article details the camera calibration process.
Description
PIX4Dmatic requires as input the internal parameters of the camera used to acquire the images for processing. These parameters are used for the 3D reconstruction and therefore, must be accurate to achieve an optimal 3D reconstruction.
PIX4Dmatic has an internal camera database with the optimal parameters for many cameras. For cameras that do not exist in PIX4Dmatic's camera database, the optimal internal camera parameters can be computed in PIX4Dmatic while processing a high-quality dataset. These parameters can then be used for all the projects acquired with the same camera. As small consumer-grade cameras are sensitive to vibration, temperature, etc., the software will, by default, optimize the internal parameters for each project starting from the same initial parameters.
Image requirements
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- Enough images (100 - 300 images).
- Non-planar scene (not all objects have the same height)
- High overlap and rich texture.
- Several grid flights (at different heights) OR oblique imagery with sufficient overlap.
- Images with NO distortion correction applied. Original images are needed.
- If possible, with Ground Control Points (GCPs).
Calibration procedure
The procedure to Calibrate a Perspective camera lens in PIX4Dmatic is described below:
- Create a new project: File > New
- Import the images: File > Import > Images
- Configure the image properties:
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- (optional, recommended) Import an image geolocation and orientation file
- Select the image coordinate system
- Edit the internal camera parameters.
- In the Camera Model Parameters section, select Perspective Lens and set the following values:
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Focal Length [mm] or [px] Set the focal length in millimeters or pixels. Principal Point x [mm] or [px] Set the principal point in the center of the image, i.e. set the value to ImageWidth/2. Principal Point y [mm] or [px] Set the principal point in the center of the image, i.e. set the value to ImageHeight/2. Radial Distortion R1 = 0 Radial Distortion R2 = 0 Radial Distortion R3 = 0 Tangential Distortion T1 = 0 Tangential Distortion T2 = 0
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- Click Apply
- Click on Calibration and select the processing settings according to the dataset.
- (optional) Import GCPs without marking them: How to import and mark ground control points (GCPs)
- Click Start.
- (optional) If the project has an image geolocation file and GCPs in a known coordinate system, mark the GCPs using the image viewer How to import and mark ground control points (GCPs).
- After marking the Ground Control Points click on the Reoptimization step.
- Verify the quality of the reconstruction by:
- Assessing the Quality Report.
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- Selecting Automatic Tie Points at different locations in the point cloud and verifying the reprojection in the image viewer.
- Selecting the GCPs in the rayCloud and verifying the reprojection in the image viewer.
- If the reconstruction is not good enough, mark Manual Tie Points in the areas that are not well reconstructed and run Reoptimization: How to import and mark Manual Tie Points (MTPs).
- Generate the Quality Report by clicking File > Export > Quality Report and repeat the following procedure until the values (before and after the Load optimized parameters button) converge.
- Open the Camera internals window and click on the Load optimized parameters button.
- Run Reoptimization.
- Open the Camera internals window and click on the Load optimized parameters button.
- Run Reoptimization.
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- Once the reconstruction is good, save the optimized camera parameters by ticking on the respective box in the Camera internals window so that they can be used as initial values for other projects.