National Instruments IMAQTM 用户手册

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To express measurements in real-world units, you must define a 
coordinate system in the image of the grid. Use 

CWIMAQLearnCalibrationOptions.CalibrationAxisInfo

 

to define a coordinate system by its origin, angle, and axis direction.

The origin, expressed in pixels, defines the center of the coordinate system. 
The angle specifies the orientation of the coordinate system with respect to 
the angle of the topmost row of dots in the grid image. The calibration 
procedure automatically determines the direction of the horizontal axis in 
the real world. The vertical axis direction can either be indirect, as shown 
in Figure 6-2a, or direct, as shown in Figure 6-2b.

Figure 6-2.  Axis Direction in the Image Plane

If you do not specify a coordinate system, the calibration process defines a 
default coordinate system. If you specify a grid for the calibration process, 
the software defines the following default coordinate system, as shown in 
Figure 6-3:

1.

The origin is placed at the center of the left, topmost dot in the 
calibration grid.

2.

The angle is set to 0

°. This aligns the x-axis with the first row of dots 

in the grid, as shown in Figure 6-3b.

3.

The axis direction is set to indirect using 

CWIMAQCoordinateSystem.AxisOrientation=

cwimaqAxisOrientationIndirect

. This aligns the y-axis to the 

first column of the dots in the grid, as shown in Figure 6-3b.

X

Y

X

Y

a.

b.