Adv. Straight Edge

NI Vision Assistant

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Adv. Straight Edge

Locates a straight edge in a region of interest.

Main Tab

The following controls are available on the Main tab.

  • Step Name—Name to give the step.
  • Reposition Region of Interest—When enabled, the step dynamically repositions the region of interest based on a coordinate system you built in a previous step.
  • Reference Coordinate System—Coordinate system to which you want to link the region of interest.

Edge Detector Settings Tab

The following controls are available on the Edge Detector Settings tab.

  • Suggest Values—When enabled, the step suggests appropriate values for the Edge Detector controls.
  • Detection Method—Specifies the method to use to find the straight edge. The following options are available:
    • First Edge Rake—Fits a straight edge on the first point detected using a Rake.
    • Best Edge Rake—Fits a straight edge on the best points detected using a Rake.
    • Best Hough Edge Rake—Fits the strongest straight edge using all points detected using a Rake.
    • First Edge Projection—Uses the location of the first projected edge as the straight edge.
    • Best Edge Projection— Finds the strongest projected edge location to determine the straight edge.
  • Search Direction—Direction in which you want the search lines to look for a straight edge within the region of interest. The following options are available:
    • Left to Right—Searches for edges within the region of interest from left to right.
    • Right to Left—Searches for edges within the region of interest from right to left.
    • Top to Bottom—Searches for edges within the region of interest from top to bottom.
    • Bottom to Top—Searches for edges within the region of interest from bottom to top.
  • Edge Polarity—Specifies the pixel intensity transitions to use to determine edges. The following options are available:
    • Any Edge—Finds edges characterized by dark-to-bright and bright-to-dark pixel intensity transitions.
    • Dark to Bright—Finds only those edges characterized by dark-to-bright pixel intensity transitions along the direction of the search line.
    • Bright to Dark—Finds only those edges characterized by bright-to-dark pixel intensity transitions along the direction of the search line.
  • Minimum Edge Strength—Minimum difference in the intensity values between the edge and its surroundings.
  • Minimum Edge SNR—Specifies the minimum signal to noise ration (SNR) of the edge points used to fit the straight line.
  • Kernel Size—Specifies the size of the edge detection kernel.
  • Gap—Specifies the size, in pixels, of the space between the search lines. This control is only used with a Rake-based Detection Method.
  • Projection Width—Specifies the number of pixels averaged perpendicular to the Search Direction to compute the edge profile strength at each point along the region of interest.
  • Interpolation—Specifies the interpolation method used to locate the edge position. The following options are available:
    • Zero Order—Rounds to the nearest integral edge location.
    • Bilinear—Uses bilinear interpolation to compute the edge location.
    • Bilinear Fixed—Uses bilinear fixed interpolation to compute the edge location.
  • Projection Method—Specifies the method used to process the data extracted by the edge detector. The following options are available:
    • Average—Averaged the data extracted for edge detection.
    • Median—Computes the median of the data extracted for edge detection.
  • Straight Edges Found—Displays the number of straight edges found by the step.
  • Search Line Index—For a Rake-based Detection Method, specifies the search line used by the Edge Strength Profile and Edge Points Found on Search Line controls.
  • Edge Index—For an Edge Projection Detection Method, specifies the index of the edge for which the Edge Strength Profile is shown.
  • Edge Strength Profile—Displays a strength profile of the edges found along the specified Search Line Index based on the current control settings.
  • Edge Points Found on Search Line—Displays information about the edge points found on the specified Search Line Index. The following information is displayed for each edge:
    • X—X-coordinate of the edge.
    • Y—Y-coordinate of the edge.
    • Strength—Strength of the edge. Higher values indicate a stronger edge.
    • STR—Signal to threshold ratio for the edge.
    • TNR—Threshold to noise ratio for the edge.
    • SNR—Signal to noise ratio for the edge.

Straight Edge Settings Tab

The following controls are available on the Straight Edge Settings tab.

  • Suggest Values—When enabled, the step suggests appropriate values for the Straight Edge Settings controls.
  • Minimum Score—Specifies the minimum score of a detected straight edge.
  • Maximum Score—Specifies the maximum score of a detected straight edge.
  • Angle Range—Specifies the positive and negative range within which the straight edge is expected to be found.
  • Angle Tolerance—Specifies the expected angular accuracy of the straight edge.
  • Minimum Coverage—Specifies the number of points, as a percentage of the number of search lines, that need to be included in the detected straight edge.
  • Maximum Iterations—Specifies the number of iterations used for a Hough Detection Method.
  • Straight Edges Requested—Specifies the number of straight edges to find in the image.
  • Straight Edges Found—Displays the number of straight edges found by the step.
  • Search Line Index—For a Rake-based Detection Method, specifies the search line used by the Edge Strength Profile and Edge Points Found on Search Line controls.
  • Edge Strength Profile—Displays a strength profile of the edges found along the specified Search Line Index based on the current control settings.
  • Edge Points Found on Search Line—Displays information about the edge points found on the specified Search Line Index. The following information is displayed for each edge:
    • X—X-coordinate of the edge.
    • Y—Y-coordinate of the edge.
    • Strength—Strength of the edge. Higher values indicate a stronger edge.
    • STR—Signal to threshold ratio for the edge.
    • TNR—Threshold to noise ratio for the edge.
    • SNR—Signal to noise ratio for the edge.

Results Tab

Displays the results for edges detected in the image.

  • Straight Edge Results—Displays information about the straight edges found in the image.
  • Straight Edges Found—Displays the number of straight edges found by the step.
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