This tool finds gaps within specified paths in an image.

Based on a geometry description for a set of paths, the PolyLineGapFinder tool detects and counts gaps along the paths.

The following results are found:

• Number of gaps found

• Positions of the gaps (gap centers)

• The longest gap

The tool works with subpixel resoultion when calibrated with a high precision grid - more information Calibrator

An interactive Polygon Wizard improves the speed and the accuracy of polygon path definitions.

For short gaps, a two step gap validation improves the accuracy of locating gaps.

• Step 1 : look for short gaps along the paths
• Step 2 : validate size and span of gap using a dynamic blob-analysis

The tool does not deliver an output reference coordinate system.

Setup

Reference - Reference system selection

Line definition file - The paths to be searched are initially read from a text file (see the StrVec format). The name of that file is also stored, for possible future reload. The path information, however, is stored directly in the system, without need for the external file.
You can browse for or manually edit the filename; by clicking "Load", the file is read and its contents stored internally. 

• Always read file at startup (overwrite SPB) - With this selection, the file is always loaded at startup.

Position

• Offset in X-direction - added to search positions
• Offset in Y-direction - added to search positions

Long gaps

• Search for long gaps - enable/disable this algorithm. A long gap is defined as the longest stretch between edges of opposite polarity (light-do-dark and dark-to-light or vice versa).

Search

• Trace step (pixels) - Number of pixels between each sample along the lines - normally 1 - given in pixels
• Line width (pixels) - Number of pixels to each side of the central to include in an averaging operation - 0 - trace line is not averaged - a higher value will average N pixels perpendicular to the trace comb
• Smooth base - Averaging filter length. 3 is normally a good value
• Smooth counter - Count of repeated averaging filter operations. 1 default
  • The smoothing increasing with higher values
• Threshold - Intensity difference to signify a gap. The threshold or sensitivity of the gap - a lower value increases the sensitivity.
• Polarity - All gaps (dark and bright) | Positive (bright gaps) | Negative (dark gaps). Search for "dark", "bright" or all gaps

Search line samples dialog

Show intensity variations along one or more search lines. Useful for setting search parameters.

• Line indices - traceline selection
  • example: 2,3,12-15
  • example: 1 3 5 7
• Show short search - use the short search filter settings
• Show search line popup - display graphs

Advanced

Shorter gaps are define to locate small gaps. Blob Search is added to verify that contrast reduction across the complete gap.

The example shows a rejected short-circuit candidate and one broken-circuit and one rejected broken circuit. Candidates are defined to comply with the Short Gap Definition.

Search

• Trace step (pixels) - Number of pixels between each sample along the lines - normally 1 - given in pixels
• Line width (pixels) - Number of pixels to each side of the central to include in an averaging operation - 0 - trace line is not averaged - a higher value will average N pixels perpendicular to the trace comb
• Smooth base - Averaging filter length. 3 is normally a good value
• Smooth counter - Count of repeated averaging filter operations. 1 default
  • The smoothing increasing with higher values
• Threshold - Intensity difference to signify a gap. The threshold or sensitivity of the gap - a lower value increases the sensitivity.
• Polarity - All gaps (dark and bright) | Positive (bright gaps) | Negative (dark gaps). Search for "dark", "bright" or all gaps
• Max length (pixels) - ignore gaps exceeding this length

Blob analysis

• Blob search width - parallel search lines are positioned 1 pixel apart along a candidate gap, defining the blob search area.
• Search for blobs Brighter than | Darker than
  • Threshold
• Threshold calculated as Percent of span | Percentile
  • this is a dynamic threshold independant of the absolute intensity of the gap
• Min blob area given in square pixels
  • 2 x 2 pixels are 4 square pixels
• Allow (and ignore) smaller blobs
• Blobs must span entire resample width

Constraints

• Min blob count
• Max blob count

Search lines