Chapter 5
Performing Machine Vision Tasks
©
National Instruments Corporation
5-11
IMAQ Vision for LabWindows/CVI User Manual
If you want to find points along a circular edge and find the circle that best
fits the edge, as shown in Figure 5-6, use
imaqFindCircularEdge()
.
Figure 5-6.
Finding a Circular Feature
Use
imaqFindEdge()
and
imaqFindConcentricEdge()
to locate the
intersection points between a set of search lines within the search region
and the edge of an object. You can specify the search region using
imaqSelectRect()
or
imaqSelectAnnulus()
. Specify the separation
between the lines that the functions use to detect edges. The functions
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 functions return the
coordinates of the edges found.
Finding Edge Points Along One Search Contour
Use
imaqSimpleEdge()
or
imaqEdgeTool2()
to find edge points along
a contour. Using
imaqSimpleEdge()
, you can find the first edge, last
edge, or all edges along the contour. Use
imaqSimpleEdge()
when your
image contains little noise and the object and background are clearly
differentiated. Otherwise, use
imaqEdgeTool2()
.
1
Annular Search Region
2
Search Lines
3
Detected Edge Points
4
Circle Fit To Edge Points
2
3
4
1
