CSI APPLICATION NOTE AN-722
EXTERNAL ORIENTATION CALIBRATION IN VIC-3D
INTRODUCTION
Calibration in Vic-3D serves to establish two distinct sets of parameters.
• Intrinsic parameters: These parameters are specific to each camera. We calculate focal length, aspect ratio, and
sensor center (the point on the sensor that corresponds to the center of the lens). These parameters will change if
you move the lens or change the aperture or focus.
• Extrinsic parameters: The parameters define the relationship between the two cameras in the stereo system. We
calculate X, Y, and Z displacements between the cameras, and 3 angles between the cameras (alpha, beta,
gamma). These parameters will change if the cameras are moved or tilted.
Typically, we calibrate extrinsic and intrinsic parameters at the same time, with a stereo calibration. However, in some
cases, it’s advantageous to calibrate the extrinsic parameters separately, or to refine them using a speckle image.
Examples of cases where separate calibration is required:
• Cameras cannot be synchronized
• Large measurement fields for which a large enough grid is not practical
For these cases, use Procedure 1.
Examples of cases where stereo calibration may be refined by external calibration:
• The cameras have been moved or bumped since calibration. In general, any time you run a correlation and see a
higher than expected projection error, you can try running the external orientation calibration to improve your
results.
• Test setups that include nonstandard distortions, such as from a glass pane
For these cases, use Procedure 2.
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