National Instruments IMAQTM 用户手册

© National Instruments Corporation

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.

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

2

3

4

1