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ExtendSegmentFromPoint

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Module: MetrologyPro

Builds a segment from a single point on a line by walking in both directions along the locally estimated line direction, one pixel at a time.

Applications

Growing a detected edge point into a full segment when only a point (not a segment) is available from a prior detection step.
Name Type Range Description
Input value inImage Image Input image (gradient is computed in-place)
Input value inPoint Point2D Starting point, expected to lie on or near the line
Input value inEdgeThreshold Real 0.0 - Minimum Sobel gradient magnitude required to continue extending
Input value inRelativeThreshold Real 0.0 - 1.0 Candidate magnitude must be at least this fraction of the running average magnitude
Input value inRoi Rectangle2D* Optional rectangle that limits pixel tracking to a specific area
Output value outSegment Segment2D Resulting segment spanning the detected line through inPoint
Output value outTrackedPoints Point2DArray Pixel centres visited during tracking, in processing order

Description

The operation starts from inPoint, which is expected to lie on or near an edge, and walks in both directions along the locally estimated edge direction one pixel at a time. At each step, two integer-valued pixel candidates straddling the current path perpendicularly are evaluated; the one with the higher Sobel gradient magnitude is chosen. The direction estimate is updated at each step by averaging with the local edge direction. Extension stops when the gradient at the next position falls below inEdgeThreshold, when the gradient falls below inRelativeThreshold × the running average, or when the image boundary (or inRoi) is reached.

Hints

  • Supply a point from a prior detection step (e.g. from ScanSingleEdge or FindSingleEdge) as inPoint.
  • Set inEdgeThreshold to match the expected edge contrast. Values between 5 and 15 work for most natural edges under moderate noise.
  • Use inRelativeThreshold to stop extension when the gradient fades near the true endpoint, preventing the path from drifting along background noise after the edge ends.
  • Connect outTrackedPoints during development to visualize the pixel-level walking path.

Complexity Level

This filter is available on Advanced Complexity Level.

See Also

  • ExtendSegment – Extends a segment at both endpoints by walking 1 pixel at a time along the segment direction, stopping when the in-place Sobel gradient magnitude at the next position drops below threshold or the image boundary is reached.
  • FindSingleEdge