Deprecated in Current Release
Defining Calibration Tasks
Definitions and Theory
Currently, Geometric Calibration in Imatest requires some assumptions about, and constraints on, the camera systems it supports.
While these constraints are relatively loose (most cameras and multi-camera setups will meet them), it is worth checking to make sure your system fits within the class of devices Imatest can calibrate.
Central Projection + Radial Distortion
Imatest currently supports estimation only of the parameters of a central projection camera model, plus the addition of radial distortion. “Central projection camera” is also known as a “pinhole camera” or “perspective camera”. Fortunately, most classes of cameras can be very well described by this model.
The most common exception to this is the set of devices with >180° field of view. (In practice, calibrating anything in the range of 150° or greater is extremely challenging.)
Line-scan or push-broom imaging devices are somewhat supported in that they can be described by a type of projective transformation, though Imatest does not make any special considerations for these imaging models.
Any operation on the camera that affects one of the measured parameters invalidates the measured calibration. The most common such operation is zooming, which changes the focal length of a camera. Not only will this obviously change the f parameter estimation, but also it will typically change the distortion function as well.
If a camera design allows variation in the parameters of geometric calibration, it will need to be tested at each setting.
Calibrating a multi-camera system with Imatest requires that each individual camera follow the above model, as well as a few further constraints. Note that these requirements hold for systems with two, three, or even more cameras.
Overlapping field of view
Imatest can only determine the positioning of devices relative to one another if it can determine common points on the target viewed by each. The views need not necessarily be extremely similar, and indeed this is rarely the case, but they do need to overlap where the target is.
Imatest presumes the cameras in a multi-cam system are always in the same fixed positioning- the cameras cannot rotate or move relative to each other.
If the system allows camera positioning changes, calibration will need to be performed at each position (or alternative can be used to verify each position).