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FitArcToStripe

Basic

Module: MetrologyPro

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

Applications

Precise detection of a ring section, 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
 inStripeScanParams StripeScanParams Parameters controlling the stripe extraction process
Input value
 inStripeSelection Selection Selection mode of stripe
Input value
 inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
Input value
 inMaxIncompleteness Real 0.0 - 0.999 Maximal fraction of stripe 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 in the middle of found stripe
Output value
 outInnerArc Arc2D? Fitted inner arc
Output value
 outOuterArc Arc2D? Fitted outer arc
Output value
 outStripes Stripe1D?Array Found stripes
Output value
 outStripePoints Point2DArray Extracted points of middle arc of an image stripe
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
 outBrightnessProfiles ProfileArray Extracted image profiles
Output value
 outResponseProfiles ProfileArray Profiles of the edge (derivative) 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 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 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 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.

Examples

Fitting an arc to the dark stripe formed on one side of a hole
(inStripeScanParams.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.
  • FitArcToRidges – Performs a series of 1D ridge detections and finds an arc that best matches the detected points.