Image Engineering
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4 DIFFERENCES BETWEEN GEOCAL AND GEOCAL XL
The key difference between GEOCAL XL and the standard GEOCAL is the physical size of the
diffractive optical element (DOE) that generates the point grid. While the standard GEOCAL has a
usable diameter of 77 mm, the GEOCAL XL provides a functional diameter of 155 mm.
Why a larger version of the GEOCAL?
A larger DOE is needed when the device under test (DUT) can not be placed directly in front of the
DOE, for example, when a car's windshield is involved. As mentioned in chapter 3.3.1, "Camera
position and suitable lenses," the generated point grid needs to cover the entire camera sensor to
provide a reliable calibration.
Figure 6: Use case for the larger DOE provided in the GEOCAL XL
As illustrated in
Figure 6
above, the windscreen angle prevents the standard GEOCAL from being
placed close enough to the camera to provide a full-frame image of the standard DOE. This angle
would result in a less precise and less reliable calibration.
