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Module: MetrologyPro

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


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


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.


  • 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.


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).


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.