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Smart Camera / Vision-Sensor / 1D-/2D-Code-Scanner / OCR Reader
11.10.2.2. Find Circle
Objective
Detect an edge.
Procedure
After the toolbar has been activated, a circle can be drawn by means of two or three
clicks.
Search rays are generated perpendicular to this circular line. In accordance with the
selected settings for edge polarity, find by and edge with, as well as positive and nega-
tive gradient threshold, an edge is searched for on each of these search rays (see sec-
tion 11.4.3.1). These detected edges form a scatter plot through which only a single
circular line is drawn, for which the clearance to the scatter plot is as small as possible.
Individual points may be detected as outliers and ignored during the next iteration step
(renewed best-fit calculation). This best-fit calculation is executed as many times as
selected under fitting iterations.
Property
The following settings/results are displayed:
Edge Polarity Expected Brightness Characteristics
Either
Both bright to dark and dark to bright transi-
tions are searched for.
Bright to Dark
Only bright to dark transitions are searched
for.
Dark to Bright
Only dark to bright transitions are searched
for.
Find by This parameter can be used to specify which of the detected edges
will be used on the search line.
Best Score
If several edge transitions are detected on the
search line, the transition with the greatest
contrast is selected.
First Score
If several edge transitions are detected on the
search line, the first transition in the search
direction is selected.
Last Score
If several edge transitions are detected on the
search line, the last transition in the search
direction is selected.
Edge Width
(px)
The setting Edge Width controls the sensitivity of brightness chang-
es.
• An Edge Width of 3 pixels represents the highest sensitivity in con-
trast in the image.
• An Edge Width of 9 pixels smoothes the gray profile to ignore the
noise.
Threshold
Gradient Pos
Threshold Gradient Pos defines the threshold of the positive gradi-
ent.
Note: The gradient represents the change of brightness from pixel to
the next. The higher the contrast of an edge the higher the gradient.
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