About camera linearization

A camera transmits coordinates in two dimensions for each marker’s center point in the field of view of the camera. The locations of the center points reflect the optical view of the sensor chip in the camera. Since this cannot be done without distortion, the QTM software must have information about the distortion of each camera in order to get correct 3D data. This correction is referred to as linearization or intrinsic calibration.

The linearization takes into account the alignment of the lens relative to the sensor (center point of the optical axis) and the optical distortion of the lens. The linearization is therefore specific for each individual camera-lens combination.

The linearization procedure of the camera generates a file that is stored in the camera's memory, and downloaded to the computer the first time you use a camera in QTM. The camera linearizations can be inspected in the Linearization page in the Project Options, see chapter Linearization.

The linearization procedure is implemented in QTM. Linearization of a camera requires a special Qualisys linearization plate. For instructions on how to linearize a camera, see chapter Linearization procedure and instructions.

All Qualisys cameras are linearized at the factory and delivered with a valid linearization file.

Linearization file warning

The linearization file in the camera is compared to the one used in QTM every time that you start a new measurement. If the files do not match, the following warning is displayed.

If you want to download the file from the camera click Yes, which is mostly recommended if the file in the camera is more recent than the one in QTM. Otherwise, click No. Optionally, check the box Do not show this message again to avoid the warning for this file the next time you start a measurement.