Camera calibration tutorial

Foreword

A calibrated camera is required to display information in augmented reality in the 3D space. AugmentedPro Creator projects with 3D augmentations have to define a target device with a camera and its calibration parameters. If the camera parameters do not correspond to the camera and its target resolution, the augmentations will either be appear on screen with wrong size and position, or not appear at all. These parameters can be obtained with the camera calibration procedure available in AugmentedPro Player.

The calibration procedure consists in taking 9 pictures of a planar calibration pattern. Visual guides are displayed as an indication of how the calibration pattern should appear in the camera image. It is not necessary to make the visual guide and the calibration pattern match exactly. A rough similarity is sufficient.

Step by step procedure

Print the pdf file containing the calibration grid

Launch AugmentedPro Player on your target device, click on the Settings button and on the Cameras tab.

Select the camera you want to calibrate, the resolution you want to use and click on the Calibrate button.

The first visual guide is displayed in semi-transparency. An information ribbon at the bottom of the screen indicates the action to perform and the remaining images to capture.
Move the camera or the calibration pattern so that the pattern matches the guide approximately. When the pattern is close to the guide click on the Snapshot button.

The processing of the image starts, it can last for a few seconds. The corners of the pattern are displayed when the process is over.

Click on the Play button to continue and repeat the process for all the images, moving either the camera or the calibration pattern.

The corners detection may fail when the calibration pattern is occluded or if a light source reflection dims the black/white contrast.

In case of failure click on the Play button to start the process again for the same point of view.

Once the nine snapshots have been recorded, the calibration parameters are computed automaticcaly.

The calibration parameters are displayed at the end of the computation with up to 5 stars that indicate the quality level of the results.

Your calibration parameters are now saved in AugmentedPro Player for the selected camera and resolution. You can retrieve these parameters in the Cameras tab of the Settings section in AugmentedPro Player. You can start a new calibration procedure for the same camera and resolution, your current calibration parameters will be overwritten with the new results even if the previous quality level was better. The parameters are overwritten when you reach the end of the calibration procedure, at the parameters computation time. You may abort a calibration procedure with the Back button at the top of the screen, previous calibration parameters will still be available in AugmentedPro Player.

Your calibration parameters can now be reported in AugmentedPro Creator when creating a project with a new device or when editing your device parameters in the Target Device tab that can be opened from the Settings menu. Export your projects with these parameters set in AugmentedPro Creator to play projects with 3D augmentations on your target device.