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

Name Type Range Description
inImage Image Image to fit segment to
inFittingField SegmentFittingField Segment 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 segment
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
inOutlierSuppression MEstimator* Selects a method for ignoring incorrectly detected points
outSegment Segment2D? Fitted segment or nothing if the fitting fails
outEdges Edge1D?Array Found edges
outDeviationProfile Profile? Profile of distances between the actual segment points and the corresponding reference segment points
outAlignedFittingField SegmentFittingField Fitting field used; in the image coordinate system
outInliers Point2DArray Points matching the fitting segment
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 straight edge, whose rough location is known beforehand.


The operation tries to fit a given segment 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 segment in the image. Only inMaxIncompleteness fraction of these scans may fail. If the fitting according to the given parameters is not possible, outSegment 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: Blade, Blister Inspection (NET GmbH), L-pipe measurements.

Fitting two segments to the edges of a blister
(inEdgeScanParams.EdgeTransition = DarkToBright, inEdgeScanParams.SmoothingStdDev = 1.0).


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 FitSegment filter group.

See Also

  • FitSegmentToRidges – Performs a series of 1D ridge detections and finds a segment that best matches the detected points.
  • FitSegmentToStripe – Performs a series of 1D stripe detections and finds a segment that best matches the detected points.