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Theory of Operation
Now look what happens as the circle is rotated about the X-axis – in two dimensions it appears to be an el-
liptical shape.
The more we rotate the circle about the x-axis, the smaller the y-axis diameter appears. In fact, a mathemati-
cal relationship exists that says if you can measure the length of the y-axis line and the length of the x-axis
(the circle’s true diameter), you can determine the angle of rotation.
To put this all together, no matter how you rotate the circle in any dimension (X, Y, Z), the true diameter axis
is always visible. This is called the ellipse’s long axis. The 3D Aligner measures every diameter on the target
dot and uses the long axis it nds as the true diameter to determine how far away the target is through per-
spective. Then, it looks at the diameters in the other dimensions that are 90 degrees to the true diameter to
nd the short axis and determines the angle of orientation away from normal with foreshortening. Using these
methods it determines where the target dot is in three-dimensional space with respect to the camera, both
distance and orientation. It is the circle’s unique characteristics that allow the aligner to distinguish between
the effects of perspective and orientation. Examine below to see and example of a target rotated in different
directions.
For this discussion we assumed the target has only one dot. In reality, each target has 33 dots (and there are
4 targets), and the 3D Aligner’s powerful computer system analyzes each circle simultaneously for incred-
ible accuracy and resolution. We have now seen how the aligner uses the camera images to determine the
targets location and orientation in 3-dimensional space. It now has the capability to measure, but how does it
use these principles to measure wheel alignment angles?
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