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Performs a series of 1D edge detections and creates a path from the detected points.

Name Type Range Description
inImage Image Image to fit the path to
inFittingField PathFittingField Path fitting field
inFittingFieldAlignment CoordinateSystem2D* Adjusts the fitting field to the position of the inspected object
inScanStep Real* 0.0 - Optional implicit conversion of the input path to an equidistant one
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
inMaxInterpolationLength Integer* 0 - Maximal number of consecutive points not found
inMaxDeviationDelta Real* 0.0 - Maximal difference between deviations of consecutive path points
inMaxIncompleteness Real 0.0 - 0.999 Maximal fraction of edge points not found
outPath Path? Fitted path or nothing if the fitting failed
outEdges Edge1D?Array Found edges
outDeviationProfile Profile? Profile of distances between the actual path points and the corresponding reference path points
outAlignedFittingField PathFittingField 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


Tracing of an object contour, whose rough location and shape is known beforehand.


The operation tries to fit a given path to edges present in the inImage image. Internally, it performs a series of scans with the ScanSingleEdge filter along a number of 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 path in the image. Only inMaxIncompleteness fraction of these scans may fail. If the fitting according to the given parameters is not possible, outPath is set to Nil.

There are also another parameters that control the path fitting process. The inMaxDeviationDelta parameter defines the maximal allowed difference between deviations of consecutive points from the input path points. If some of the scans fail or if some of found points are classified to be wrong according to another control parameters, output path points corresponding to them are interpolated depending on points in their nearest vicinity. No more than inMaxInterpolationLength consecutive points can be interpolated. The exception to this behavior are points which were not found on both ends of the input path. Those are not part of the result at all.


  • 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.
  • Use the diagScanSegments and outEdges outputs to visualize the scanning results.


Fitting a path to the edges of a plastic capsule
(inEdgeSelection = First, inEdgeScanParams.EdgeTransition = 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 FitPath filter group.

See Also

  • FitPathToRidges – Performs a series of 1D ridge detections and creates a path from the detected points.
  • FitPathToStripe – Performs a series of 1D stripe detections and creates a path from the detected points.