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FitCircleToStripe

Basic

Module: MetrologyPro

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

Applications

Precise detection of ring-shaped objects, whose rough location is known beforehand.
Name Type Range Description
Input value inImage Image Image to fit the circle to
Input value inFittingField CircleFittingField Circle fitting field
Input value inFittingFieldAlignment CoordinateSystem2D* Adjusts the fitting field to the position of the inspected object
Input value inScanCount Integer 3 - The number of points that will be searched to estimate the position of the circle
Input value inScanWidth Integer 1 - The width of each scan field (in pixels)
Input value inSamplingParams SamplingParams Parameters controlling the sampling process
Input value inStripeScanParams StripeScanParams Parameters controlling the stripe extraction process
Input value inStripeSelection Selection Selection mode of stripe
Input value inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
Input value inMaxIncompleteness Real 0.0 - 0.999 Maximal fraction of stripe points not found
Input value inFittingMethod CircleFittingMethod Method used to fit a circle
Input value inOutlierSuppression MEstimator* Selects a method for ignoring incorrectly detected points
Output value outCircle Circle2D? Fitted circle in the middle of found stripe
Output value outInnerCircle Circle2D? Fitted inner circle
Output value outOuterCircle Circle2D? Fitted outer circle
Output value outStripes Stripe1D?Array Found stripes
Output value outStripePoints Point2DArray Extracted points of middle circle of an image stripe
Output value outDeviationProfile Profile? Profile of distances between the actual circle points and the corresponding reference circle points
Output value outAlignedFittingField CircleFittingField Fitting field used; in the image coordinate system
Output value outBrightnessProfiles ProfileArray Extracted image profiles
Output value outResponseProfiles ProfileArray Profiles of the edge (derivative) operator response
Diagnostic input diagScanSegments Segment2DArray Segments along which the scans were run
Diagnostic input diagSamplingAreas Rectangle2DArray Areas from which the input image is sampled

Description

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

Examples

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

Fitting a circle to the dark circular stripe of a washer
(inStripeScanParams.Polarity = Dark).

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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of FitCircle filter group.

See Also

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