Chapter 6
Calibration
©
National Instruments Corporation
6-7
IMAQ Vision for LabWindows/CVI User Manual
IMAQ_PERSPECTIVE
to choose the perspective calibration algorithm.
Learning and applying perspective projection is less computationally
intensive than the nonlinear method. However, perspective projection
cannot handle nonlinear distortions.
If your imaging setup exhibits nonlinear distortion, use the nonlinear
method. The nonlinear method guarantees accurate results only in the area
that the calibration grid covers, as shown in Figure 6-6. If your system
exhibits both perspective and nonlinear distortion, use the nonlinear
method to correct for both. Set the
mode
element of the
options
parameter
to
IMAQ_NONLINEAR
to choose the nonlinear calibration algorithm.
Figure 6-6.
Calibration ROIs
Using the Learning Score
The learning process returns a score that reflects how well the software
learned the input image. A high learning score indicates that you chose the
the appropriate learning algorithm, that the grid image complies with the
guideline, and that your vision system setup is adequate.
If the learning process returns a low score, try the following:
1.
Make sure your grid complies with the guidelines listed in the
Defining a Calibration Template
section.
2.
Check the lighting conditions. If you have too much or too little
lighting, the software may estimate the center of the dots incorrectly.
1
Calibration ROI Using the
Perspective Algorithm
2
Calibration ROI Using the Nonlinear
Algorithm
1
2
