Chapter
4
Reference Manual
IVC-2D
94
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SICK AG • Advanced Industrial Sensors • www.sick.com • All rights reserved
Edge
Find Circle Edges
This tool evaluates the variation of gray values and detects edges along the circumference
of a circle or ellipse. In general two evaluation types are available.
Relative evaluation:
This type detects pixels with a gray value variation above a
relative gray value threshold.
Absolute evaluation: This type detects pixels with a gray value variation above or
below two absolute gray value thresholds.
Each evaluation type has specific input parameters to optimize the edge detection. The
definition of these input parameters is shown in the figures below.
The evaluation starts at the horizontal axis of the circle (ellipse) and continues counter
clockwise along the circumference.
The tool writes the X and Y coordinates of the detected pixels into a user defined row in
the table. Additionally the tool returns the total number of indicated pixels and sets an error
flag to control the correct execution.
To set the thresholds with a slider, double-click the input field for the gray value threshold
and click the appearing button that opens a larger image. Use the left mouse button to
move the slider. It is also possible to set the shape and position of the circle (ellipse) with
the left mouse button in this window. All found edges on the circumference are marked
with red crosses.
Figure – Edge finding using relative evaluation.
A relative change of gray values is detected. Note that the Min edge distance value should
be greater than the Scan interval value to avoid misplaced results.
1
2
3
4
Average pixels
:
Value 2 means gray values
will be averaged out
of two pixels.
Scan interval
:
Distance of pixels that
will be compared.
Min edge distance
:
Number of pixels that
will skipped if one edge
was found.
Scan interval