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# FitCircleToRidges_Direct

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

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

### Syntax

C++
C#

void avl::FitCircleToRidges_Direct
(
const avl::Image& inImage,
const avl::CircleFittingField& inFittingField,
atl::Optional<const avl::CoordinateSystem2D&> inFittingFieldAlignment,
int inScanCount,
int inScanWidth,
const avl::SamplingParams& inSamplingParams,
const avl::RidgeScanParams& inRidgeScanParams,
avl::Selection::Type inRidgeSelection,
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::Ridge1D> >&> outRidges = atl::NIL,
atl::Optional<atl::Conditional<avl::Profile>&> outDeviationProfile = atl::NIL,
atl::Optional<avl::CircleFittingField&> outAlignedFittingField = atl::NIL,
atl::Optional<atl::Array<avl::Point2D>&> outInliers = atl::NIL,
atl::Array<avl::Segment2D>& diagScanSegments,
atl::Array<avl::Rectangle2D>& diagSamplingAreas,
atl::Array<avl::Profile>& diagBrightnessProfiles,
atl::Array<avl::Profile>& diagResponseProfiles
)


### Parameters

Name Type Range Default Description
inImage const Image& Image to fit the circle to
inFittingField const CircleFittingField& Circle fitting field
inFittingFieldAlignment Optional<const CoordinateSystem2D&> NIL Adjusts the fitting field to the position of the inspected object
inScanCount int 3 - 10 The number of points that will be searched to estimate the position of the circle
inScanWidth int 1 - 5 The width of each scan field (in pixels)
inSamplingParams const SamplingParams& Parameters controlling the sampling process
inRidgeScanParams const RidgeScanParams& RidgeScanParams ( ProfileInterpolation: Quadratic4 SmoothingStdDev: 1.0f RidgeWidth: 5 RidgeMargin: 2 MinMagnitude: 5.0f RidgePolarity: Dark ) Parameters controlling the ridge extraction process
inRidgeSelection Selection::Type Selection mode of ridges
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker ridges can be detected in the vicinity of stronger ridges
inMaxIncompleteness float 0.0 - 0.999 0.1f Maximal fraction of ridge 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
outRidges Optional<Array<Conditional<Ridge1D> >&> NIL Found ridges
outDeviationProfile Optional<Conditional<Profile>&> NIL Profile of distances between the actual circle points and the corresponding reference circle points
outAlignedFittingField Optional<CircleFittingField&> NIL Fitting field used; in the image coordinate system
outInliers Optional<Array<Point2D>&> NIL Points matching the fitting Circle
diagScanSegments Array<Segment2D>& Segments along which the scans were run
diagSamplingAreas Array<Rectangle2D>& Areas from which the input image is sampled
diagBrightnessProfiles Array<Profile>& Extracted image profiles
diagResponseProfiles Array<Profile>& Profiles of the ridge operator response

### Optional Outputs

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

### 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_Direct filter along inScanCount specific scan segments which length is always equal to the inFittingField width and cannot be less than 4. 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 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 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 outRidges outputs to visualize the scanning results.

### Examples

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

### 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.