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Header: AVL.h
Namespace: avl
Module: MetrologyPro

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

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


void avl::FitCircleToEdges
	const avl::Image& inImage,
	const CircleFittingMap& inFittingMap,
	const EdgeScanParams& inEdgeScanParams,
	avl::Selection::Type inEdgeSelection,
	atl::Optional<const avl::LocalBlindness&> inLocalBlindness,
	float inMaxIncompleteness,
	avl::CircleFittingMethod::Type inFittingMethod,
	atl::Optional<avl::MEstimator::Type> inOutlierSuppression,
	atl::Conditional<avl::Circle2D>& outCircle,
	atl::Optional<atl::Array<atl::Conditional<avl::Edge1D>>&> outEdges = atl::NIL,
	atl::Optional<atl::Conditional<avl::Profile>&> outDeviationProfile = atl::NIL,
	atl::Optional<atl::Array<avl::Point2D>&> outInliers = atl::NIL,
	atl::Optional<atl::Array<avl::Profile>&> outBrightnessProfiles = atl::NIL,
	atl::Optional<atl::Array<avl::Profile>&> outResponseProfiles = atl::NIL


Name Type Range Default Description
Input value
inImage const Image& Image to fit the circle to
Input value
inFittingMap const CircleFittingMap& Input fitting map
Input value
inEdgeScanParams const EdgeScanParams& Parameters controlling the edge extraction process
Input value
inEdgeSelection Selection::Type SelectionBest Selection mode of edges
Input value
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
Input value
inMaxIncompleteness float 0.0 - 0.999 0.1f Maximal fraction of edge points not found
Input value
inFittingMethod CircleFittingMethod::Type AlgebraicTaubin Method used to fit a circle
Input value
inOutlierSuppression Optional<MEstimator::Type> NIL Selects a method for ignoring incorrectly detected points
Output value
outCircle Conditional<Circle2D>& Fitted circle or nothing if the fitting fails
Output value
outEdges Optional<Array<Conditional<Edge1D>>&> NIL Found edges
Output value
outDeviationProfile Optional<Conditional<Profile>&> NIL Profile of distances between the actual circle points and the corresponding reference circle points
Output value
outInliers Optional<Array<Point2D>&> NIL Points matching the fitting Circle
Output value
outBrightnessProfiles Optional<Array<Profile>&> NIL Extracted image profiles
Output value
outResponseProfiles Optional<Array<Profile>&> NIL Profiles of the edge (derivative) operator response

Optional Outputs

The computation of following outputs can be switched off by passing value atl::NIL to these parameters: outEdges, outDeviationProfile, outInliers, outBrightnessProfiles, outResponseProfiles.

Read more about Optional Outputs.


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 using inFittingMap previously generated from the object being fitted. 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.


  • Connect an input image to the inImage input.
  • Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
  • 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 outEdges outputs to visualize the scanning results.


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


Read more about Local Coordinate Systems in Machine Vision Guide: Local Coordinate Systems.

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.

See Also

  • FitCircleToRidges – Performs a series of 1D ridge detections and finds a circle that best matches the detected points.
  • FitCircleToStripe – Performs a series 1D stripe detections and finds a circle that best matches the detected points.
  • FitCircleToEdges_Direct – Performs a series of 1D edge detections and finds a circle that best matches the detected points.