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FitCircleToEdges

Performs a series of 1D edge detections and finds a circle that best matches the detected points.

Name	Type	Range	Description
inImage	Image		Image to fit the circle to
inFittingField	CircleFittingField		Circle fitting field
inFittingFieldAlignment	CoordinateSystem2D *		Adjusts the fitting field to the position of the inspected object
inScanCount	Integer	3 -	The number of points that will be searched to estimate the position of the circle
inScanWidth	Integer	1 -	The width of each scan field (in pixels)
inImageInterpolation	InterpolationMethod		Interpolation method used for extraction of image pixel values
inEdgeScanParams	EdgeScanParams		Parameters controlling the edge extraction process
inEdgeSelection	Selection		Selection mode of edges
inLocalBlindness	LocalBlindness *		Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
inMaxIncompleteness	Real	0.0 - 0.999	Maximal fraction of edge points not found
inFittingMethod	CircleFittingMethod		Method used to fit a circle
inOutlierSuppression	MEstimator *		Selects a method for ignoring incorrectly detected points
outCircle	Circle2D ?		Fitted circle or nothing if the fitting fails
outEdges	Edge1D ?Array		Found edges
outDeviationProfile	Profile ?		Profile of distances between the actual circle points and the corresponding reference circle points
outAlignedFittingField	CircleFittingField		Fitting field used; in the image coordinate system
diagScanSegments	Segment2D Array		Segments along which the scans were run
diagSamplingAreas	Rectangle2D Array		Areas from which the input image is sampled
diagBrightnessProfiles	Profile Array		Extracted image profiles
diagResponseProfiles	Profile Array		Profiles of the edge (derivative) operator response

Applications

Precise detection of a circular object or hole, whose rough location is known beforehand.

Description

The operation tries to fit a given circle to edges present in the inImage image. Internally, it performs a series of scans with the ScanSingleEdge filter along inScanCount specific scan segments which length is always equal to the inFittingField width. The found points are then used to determine the actual position of the circle in the image. Only inMaxIncompleteness fraction of these scans may fail. If the fitting according to the given parameters is not possible, outCircle is set to Nil.

Hints

Connect an input image to the inImage input.
If the object location is variable, connect inFittingFieldAlignment to an appropriate local coordinate system (e.g. from a template matching filter).
Define the inFittingField input to specify the area in which edge scanning will be performed.
Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
If the noise level is high, try increasing inScanWidth and/or inEdgeScanParams.SmoothingStdDev.
If no or too few edge points are found, try decreasing inEdgeScanParams.MinMagnitude.
If some of the scans may fail, set the inMaxIncompleteness input accordingly.
If some of the scans may produce false results, try different values of the inOutlierSuppression input.
Use the diagScanSegments and outEdges outputs to visualize the scanning results.

Examples

Description of usage of this filter can be found in examples and tutorial: Badge Measurement, Gasket Inspection, Radiator Holes, Shape Fitting: Measuring holes, Shape Fitting: Gasket.

Fitting a circles to the edges of a hole
(inEdgeScanParams.Transition = BrightToDark).

Remarks

For more information about local coordinate systems please refer to the following article.

This filter is a part of the Shape Fitting toolset. To read more about this technique, one can refer to the Shape Fitting chapter of our Machine Vision Guide

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filters is member of FitCircle filter group.