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FitArcToRidges


Module: MetrologyPro

Performs a series of 1D ridge detections and finds an arc that best matches the detected points.

Applications

Precise detection of a thin arciform line, whose rough location is known beforehand.
Name Type Range Description
Input value inImage Image Input image to fit arc to
Input value inFittingField ArcFittingField Arc 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 arc
Input value inScanWidth Integer 1 - The width of each scan field (in pixels)
Input value inSamplingParams SamplingParams Parameters controlling the sampling process
Input value inRidgeScanParams RidgeScanParams Parameters controlling the ridge extraction process
Input value inRidgeSelection Selection Selection mode of ridges
Input value inLocalBlindness LocalBlindness* Defines conditions in which weaker ridges can be detected in the vicinity of stronger ridges
Input value inMaxIncompleteness Real 0.0 - 0.999 Maximal fraction of ridge points not found
Input value inFittingMethod CircleFittingMethod Method used to fit an arc
Input value inOutlierSuppression MEstimator* Selects a method for ignoring incorrectly detected points
Output value outArc Arc2D? Fitted arc or nothing if the fitting fails
Output value outRidges Ridge1D?Array Found ridges
Output value outDeviationProfile Profile? Profile of distances between the actual arc points and the corresponding reference arc points
Output value outAlignedFittingField ArcFittingField Fitting field used; in the image coordinate system
Output value outInliers Point2DArray Points matching the fitting Arc
Output value outBrightnessProfiles ProfileArray Extracted image profiles
Output value outResponseProfiles ProfileArray Profiles of the ridge 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 arc to ridges present in the inImage image. Internally, it performs a series of scans with the ScanSingleRidge 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 arc in the image. Only inMaxIncompleteness fraction of these scans may fail. If the fitting according to the given parameters is not possible, outArc 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 ridge scanning will be performed.
  • Define inRidgeScanParams.RidgePolarity to detect a particular ridge type, and only that type.
  • Adjust inRidgeScanParams.RidgeWidth to the expected thickness of the ridge (in pixels).
  • If the noise level is high, try increasing inScanWidth and/or inRidgeScanParams.SmoothingStdDev.
  • If no or too few ridge points are found, try decreasing inRidgeScanParams.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 outRidges outputs to visualize the scanning results.

Examples

Fitting an arc to a curved wall of a plastic capsule
(inRidgeScanParams.RidgeWidth = 3, inRidgeScanParams.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 FitArc filter group.

See Also

  • FitArcToEdges – Performs a series of 1D edge detections and finds an arc that best matches the detected points.
  • FitArcToStripe – Performs a series of 1D stripe detections and finds an arc that best matches the detected points.