National Instruments IMAQTM - Manual (Page 63)

Chapter 5 Performing Machine Vision Tasks
© National Instruments Corporation 5-11 IMAQ Vision for Visual Basic User Manual
Figure 5-6. Finding a Circular Feature
These methods locate the intersection points between a set of search
lines in the search region and the edge of an object. Specify the separation
between the lines that the methods use to detect edges. The methods
determine the intersection points based on their contrast, width, and
steepness. The software calculates a best-fit line with outliers rejected or a
best-fit circle through the points it found. The methods return the
coordinates of the edges found.
Finding Edge Points Along One Search Contour
Use CWIMAQVision.SimpleEdge and CWIMAQVision.FindEdges2 to
find edge points along a contour. You can find the first edge, last edge, or
all edges along the contour. Use
CWIMAQVision.SimpleEdge when the
image contains little noise and the object and background are clearly
differentiated. Otherwise, use
CWIMAQVision.FindEdges2 .
These methods require you to input the coordinates of the points along the
search contour. Use
CWIMAQVision.RegionsProfile to obtain the
coordinates from a CWIMAQRegions object that describes the contour.
If you have a straight line, use
CWIMAQVision.GetPointsOnLine to
obtain the points along the line instead of using regions.
These methods determine the edge points based on their contrast and slope.
You can specify if you want to find the edge points using subpixel accuracy.
1 Annular Search Region
2 Search Lines
3 Detected Edge Points
4 Circle Fit To Edge Points
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3
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