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


void avl::FitArcToEdges
	const avl::Image& inImage,
	const avl::ArcFittingMap& 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::Arc2D>& outArc,
	atl::Optional<atl::Array<atl::Conditional<avl::Edge1D> >&> outEdges = atl::NIL,
	atl::Optional<atl::Conditional<avl::Profile>&> outDeviationProfile = atl::NIL,
	atl::Array<avl::Profile>& diagBrightnessProfiles,
	atl::Array<avl::Profile>& diagResponseProfiles


Name Type Range Default Description
inImage const Image& Input image to fit arc to
inFittingMap const ArcFittingMap& Input fitting map
inEdgeScanParams const EdgeScanParams& Parameters controlling the edge extraction process
inEdgeSelection Selection::Type Selection::​Best Selection mode of edges
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
inMaxIncompleteness float 0.0 - 0.999 0.1f Maximal fraction of edge points not found
inFittingMethod CircleFittingMethod::Type AlgebraicTaubin Method used to fit an arc
inOutlierSuppression Optional<MEstimator::Type> NIL Selects a method for ignoring incorrectly detected points
outArc Conditional<Arc2D>& Fitted arc or nothing if the fitting fails
outEdges Optional<Array<Conditional<Edge1D> >&> NIL Found edges
outDeviationProfile Optional<Conditional<Profile>&> NIL Profile of distances between the actual arc points and the corresponding reference arc points
diagBrightnessProfiles Array<Profile>& Extracted image profiles
diagResponseProfiles Array<Profile>& 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: outArc, outEdges, outDeviationProfile.

Read more about Optional Outputs.


The operation tries to fit a given arc 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 arc in the image. Only inMaxIncompleteness fraction of these scans may fail. If the fitting according to the given parameters is not possible, outArc 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 an arc to the edges of a semi-hole
(inEdgeScanParams.Transition = BrightToDark).


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.

See Also

  • CreateArcFittingMap – Precomputes a data object that is required for fast arc fitting on images.
  • FitArcToRidges – Performs a series of 1D ridge detections and finds an arc that best matches the detected points.
  • FitArcToStripe – Performs a series of 1D stripe detections and finds an arc that best matches the detected points.