National Instruments IMAQ Vision for LabWindows TM /CVI - Manual (Page 56)

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