You are here: Start » Function Reference » Computer Vision » Shape Fitting » FitCircleToEdges

FitCircleToEdges

Header:	FIL.h
Namespace:	fil
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.

Syntax

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

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Image to fit the circle to
inFittingMap	const CircleFittingMap&			Input fitting map
inEdgeScanParams	const EdgeScanParams&			Parameters controlling the edge extraction process
inEdgeSelection	Selection::Type		SelectionBest	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 a circle
inOutlierSuppression	Optional<MEstimator::Type>		NIL	Selects a method for ignoring incorrectly detected points
outCircle	Conditional<Circle2D>&			Fitted circle 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 circle points and the corresponding reference circle points
outInliers	Optional<Array<Point2D>&>		NIL	Points matching the fitting Circle
outBrightnessProfiles	Optional<Array<Profile>&>		NIL	Extracted image profiles
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 ftl::NIL to these parameters: outEdges, outDeviationProfile, outInliers, outBrightnessProfiles, outResponseProfiles.

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 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.

Hints

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.

Examples

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

Remarks

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.