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FitCircleToRidges

Performs a series of 1D ridge 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
inRidgeScanParams	RidgeScanParams		Parameters controlling the ridge extraction process
inRidgeSelection	Selection		Selection mode of ridges
inLocalBlindness	LocalBlindness *		Defines conditions in which weaker ridges can be detected in the vicinity of stronger ridges
inMaxIncompleteness	Real	0.0 - 0.999	Maximal fraction of ridge 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
outRidges	Ridge1D ?Array		Found ridges
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 ridge operator response

Applications

Precise detection of a thin circular line, whose rough location is known beforehand.

Description

The operation tries to fit a given circle to ridges present in the inImage image. Internally, it performs a series of scans with the ScanSingleRidge 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 ridge scanning will be performed.
Define inRidgeScanParams.RidgePolarity to detect a particular ridge type, and only that type.
Adjust inRidgeScanParams.RidgeWidth to the expected thickness of the ridge (in pixels).
If the noise level is high, try increasing inScanWidth and/or inRidgeScanParams.SmoothingStdDev.
If no or too few ridge points are found, try decreasing inRidgeScanParams.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 outRidges outputs to visualize the scanning results.

Examples

Description of usage of this filter can be found in examples and tutorial: Fertilizer Granulation.

Fitting a circle to a wall of a plastic capsule
(inRidgeScanParams.Polarity = Dark, inRidgeScanParams.RidgeWidth = 3).

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.