Back to Adaptive Vision Studio website

You are here: Start » Filter Reference » Shape Fitting » FitCircleToEdges


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

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)
inImageInterpolation InterpolationMethod Interpolation method used for extraction of image pixel values
inEdgeScanParams EdgeScanParams Parameters controlling the edge extraction process
inEdgeSelection Selection Selection mode of edges
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 edge 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 or nothing if the fitting fails
outEdges Edge1D?Array Found edges
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


Precise detection of a circular object or hole, whose rough location is known beforehand.


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 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 edge scanning will be performed.
  • Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
  • If the noise level is high, try increasing inScanWidth and/or inEdgeScanParams.SmoothingStdDev.
  • 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 diagScanSegments and outEdges outputs to visualize the scanning results.


Description of usage of this filter can be found in examples and tutorial: Badge Measurement, Gasket Inspection, Radiator Holes, Shape Fitting: Measuring holes, Shape Fitting: Gasket.

Fitting a circles to the edges of a 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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of FitCircle filter group.

See Also

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