National Instruments IMAQ Vision for LabWindows TM /CVI - Manual (Page 64)

Chapter 5 Performing Machine Vision Tasks
IMAQ Vision for LabWindows/CVI User Manual 5-12 ni.com
These functions require you to input the coordinates of the points along the
search contour. Use
imaqROIProfile() to obtain the coordinates along
the edge of each contour in an ROI. If you have a straight line, use
imaqGetPointsOnLine() to obtain the points along the line instead of
using an ROI.
These functions determine the edge points based on their contrast and
slope. You can specify whether you want to find the edge points using
subpixel accuracy.
Finding Edge Points Along Multiple Search Contours
Use imaqRake() , imaqSpoke() , and imaqConcentricRake() to find
edge points along multiple search contours. These functions behave similar
to
imaqEdgeTool2() , but they find edges on multiple contours. Pass in an
ROI to define the search region for these functions.
The imaqRake() function works on a rectangular search region. The
search lines are drawn parallel to the orientation of the rectangle. Control
the number of search lines in the region by specifying the distance, in
pixels, between each line. Specify the search direction as left to right or
right to left for a horizontally oriented rectangle. Specify the search
direction as top to bottom or bottom to top for a vertically oriented
rectangle.
The imaqSpoke() function works on an annular search region, scanning
the search lines that are drawn from the center of the region to the outer
boundary and that fall within the search area. Control the number of lines
in the region by specifying the angle, in degrees, between each line. Specify
the search direction as either going from the center outward or from the
outer boundary to the center.
The imaqConcentricRake() function works on an annular search
region. The concentric rake is an adaptation of the Rake to an annular
region. IMAQ Vision does edge detection along search lines that occur
in the search region and that are concentric to the outer circular boundary.
Control the number of concentric search lines that are used for the edge
detection by specifying the radial distance between the concentric lines
in pixels. Specify the direction of the search as either clockwise or
counterclockwise.