Network Card User Manual

Chapter 5 Performing Machine Vision Tasks
IMAQ Vision for LabWindows/CVI User Manual 5-4 ni.com
Using Edge Detection to Build a Coordinate Transform
You can build a coordinate transform using two edge detection techniques.
Use
imaqFindTransformRect() to define a coordinate system using
one rectangular region. Use
imaqFindTransformRects() to define a
coordinate system using two independent rectangular regions. Follow these
steps to build a coordinate transform using edge detection.
Note To use this technique, the object cannot rotate more than ±65° in the image.
1. Specify one or two rectangular ROIs.
a. If you use
imaqFindTransformRect(), specify one rectangular
ROI that includes part of two straight, nonparallel boundaries of
the object, as shown in Figure 5-2. This rectangular region must
be large enough to include these boundaries in all the images you
want to inspect.
Figure 5-2. Coordinate Systems of a Reference Image and Inspection Image
1 Search Area for the Coordinate System
2 Object Edges
3 Origin of the Coordinate System
4 Measurement Area
1
4
1
4
a. b.
2
3
3
2