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FindMultipleLines (FindLines Multiple)

Basic

Module: MetrologyPro

Finds multiple straight lines within a rectangular scan field, ordered from highest-scoring to lowest.

Applications

Detection of multiple lines within a single scan field.
Name Type Range Description
Input value inImage Image Input image
Input value inScanField SegmentScanField Region where the scans are performed
Input value inScanFieldAlignment CoordinateSystem2D*
Input value inScanWidth Integer 1 - How many pixels are sampled perpendicularly at each scan line's positions
Input value inScanStep Integer 1 - Pixel distance between the centers of consecutive scan lines
Input value inScanLimit Integer 1 - Maximum number of scan lines
Input value inEdgeScanParams EdgeScanParams Parameters of 1D edge detection along a single scan line
Input value inPointBlindness Real 0.0 - 1.0 Defines a threshold for rejecting edge points that are weaker than a certain portion of the strongest edge point
Input value inMaxSlant Real 0.0 - 45.0 Maximum angle deviation of the resulting line from 90 degrees to the scan axis
Input value inMinLength Real 0.0 - Minimum length of the resulting line
Input value inMaxGap Real 0.0 - Maximum gap within a resulting line
Input value inMinPointCount Integer 2 - Minimum number of edge points that a resulting line must contain (otherwise it is rejected)
Input value inLineSelection LineSelection Selection criteria for edge lines
Input value inLineBlindness Real 0.0 - 1.0 Defines a threshold for rejecting entire lines that are weaker than a certain portion of the strongest line
Input value inEdgeMeasure EdgeMeasure Several options for measuring a single edge point
Input value inLineFinderMethod LineFinderMethod Several alternative algorithms for finding lines within the detected cloud of edge points
Input value inMaxPointDeviation Real 0.0 - Maximum pixel distance between a detected line and its supporting edge points
Input value inMaxTurnAngle Real 0.0 - 90.0 Maximum turn angle at any interior vertex of the line path
Input value inOutlierSuppression LineMEstimator* A method for removing outlying points
Input value inRefineEndpoints Bool Turns on a method for refining the length of the detected line
Input value inMaxCount Integer* 1 - Maximum number of lines to return
Output value outLines Segment2DArray
Output value outLineStrengths RealArray
Output value outResponseProfiles ProfileArray Edge response profiles, one per scan line
Output value outAlignedScanField SegmentScanField
Output value outSelectedPoints Point2DArrayArray Lists of points associated with each returned line
Diagnostic input diagScanLines Segment2DArray Positions of the scan lines placed within the scan field
Diagnostic input diagCandidatePoints Point2DArray Edge points detected on the scan lines, after inPointBlindness filtering

Description

The operation finds all straight lines within the inScanField and returns them ordered from the highest-scoring to the lowest. It works like FindSingleLine, but iterates the selection: once a line is accepted, its supporting candidate points are excluded from the competition for subsequent lines, so the results are non-overlapping. Up to inMaxCount lines are returned.

Hints

  • Activate diagCandidatePoints and diagScanLines during development to verify that candidates appear on the right scan lines before adjusting higher-level parameters.
  • Adjust inEdgeScanParams.MinMagnitude first: a value that is too high misses real edges; too low fills the result with noise candidates.
  • Increase inScanStep to speed up execution on large scan fields. Keep it small (5–10 px) when the line is short or its position varies rapidly across the field.
  • inPointBlindness suppresses weak per-scan-line candidates relative to the strongest response on that line. A value of 0.3 discards candidates below 30 % of the highest value on that scan line.
  • If a detected segment is shorter than the actual line, try increasing inMaxGap, widening inMaxPointDeviation.
  • Set inMaxSlant to the maximum expected deviation of the line from the direction perpendicular to the scan field axis. Narrowing this range reduces false positives.
  • Use inLineSelection = Fittest for the straightest line, Strongest for the highest-contrast line, and Smoothest for gently curved or slightly wavy lines.
  • Connect inScanFieldAlignment to a coordinate system to automatically adapt the measurement to the object position in each frame.
  • Set inMaxCount to the exact number of parallel lines expected to prevent spurious detections and unnecessary computation.
  • Increase inLineBlindness to reject weak secondary lines; decrease it to include fainter candidates.

Examples

FindMultipleLines locating two intersecting lines. The dashed rectangle is the scan field, the blue and yellow dots are candidates selected for two lines, and the green lines are detected lines.

Remarks

Read more about Local Coordinate Systems in Machine Vision Guide: Local Coordinate Systems.

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 FindLines filter group visible as Multiple.

See Also

  • FindSingleLine – Finds a single straight line within a rectangular scan field.