Rockwell Automation 5370-CVIM2 Module - Manual (Page 360)

Chapter 7
Inspection Tools
7–122
atan –– The “ atan ” (arc tangent) function calculates the arc tangent (angle)
on the basis of the tangent value that you enter after the opening parenthesis.
Thus, if you enter
atan(.5) as a standalone formula, and then pick the
Nominal field in the tool edit panel, 26.565 (the arc tangent of 0.500) will
appear in the Nominal field. Similarly, if you enter atan(–.5) , –26.565 will
appear.
Note that the acceptable range of arc tangent values is 0.0 to
1.
atan2 –– The “ atan2 ” (arc tangent “2”) function calculates the arc tangent
(angle) on the basis of entering positive and negative Y–axis and X–axis
values after the opening parenthesis. It takes the form “
atan2(y,x) ,” where y
is the Y–axis value and x is the X–axis value.
The unique aspect of the atan2 function is its ability to identify the quadrant
in which an angle is located. It makes this distinction on the basis of the signs
of the Y–axis and X–axis values. Thus, if you enter
atan2(20,20) as a
standalone formula, and then pick the Nominal field in the tool edit panel,
45.000
° (the arc tangent of 20 B 20 or 1.000) will appear in the
Nominal
field.
Similarly, atan2(–20,20) yields –45.000
°,
atan2(–20,–20) yields
–135.000
°, and
atan2(20,–20) yields 135.000
°. Thus, while each tangent
value (that is, y
B x) in each of these examples is "1.000, the four possible
combinations of the signs of x and y enables the atan2 function to determine
the specific quadrant in which the angle is located.
In the CVIM2 image coordinate system, which is shown in Figure 7.96 (page
7–123), the angles are derived as indicated on the basis of the signs of x and y.