Find Straight Edge Controls

NI Vision Builder

Locate Features Tab

Find Straight Edge Controls

Main Tab

The following controls are available on the Main tab.

Control Name Description
Step Name Name to give the step.
Region of Interest The region of interest you want to use for 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.

Settings Tab

The following controls are available on the Settings tab.

Control Name Description
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 from left to right.
  • Right to Left—Searches for edges from right to left.
  • Top to Bottom—Searches for edges from top to bottom.
  • Bottom to Top—Searches for edges from bottom to top.
Edge Polarity Specifies the pixel intensity transitions to use to determine edges. The following options are available:
  • All Edges—Finds edges characterized by dark-to-bright and bright-to-dark pixel intensity transitions.
  • Dark to Bright Only—Finds only those edges characterized by dark-to-bright pixel intensity transitions along the direction of the search line.
  • Bright to Dark Only—Finds only those edges characterized by bright-to-dark pixel intensity transitions along the direction of the search line.
Look For Specifies the type of edges to find in the image. The following options are available:
  • First Edge—Finds only the first edge of the specified polarity along each independent search line based on the direction of the search line.
  • Best Edge—Finds only the best edge of the specified polarity along each independent search line.
Auto Setup When enabled, the step automatically locates the strongest edge in the region of interest and returns the parameters it used to find the edge.
Minimum Edge Strength Minimum difference in the intensity values between the edge and its surroundings.
Kernel Size Specifies the size of the edge detection kernel.
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.
Gap Specifies the size, in pixels, of the space between the search lines.
Edge Strength Profile Graphical representation of the edge contrast along the search line specified by the Search Line Index.
Search Line Index Specifies the index of the search line represented in the Edge Strength Profile.

Advanced Tab

The following controls are available on the Advanced tab.

Control Name Description
Edge Strength Profile A graphical representation of the edge contrast along the specified search line. The yellow line indicates the location of the found edge.
Search Line Index Specifies the index of the search line represented in the Edge Strength Profile.
Edge Points Found Displays information about the edge points found along all the search lines in the ROI. The following information is displayed for each edge:
  • Strength—Strength of the edge. Values range from 0 to 1000 with larger values indicating a stronger edge.
  • STR—Signal to threshold ratio for the edge, expressed in decibels.
  • TNR—Threshold to noise ratio for the edge, expressed in decibels.
  • SNR—Signal to noise ratio for the edge, expressed in decibels.

Limits Tab

The following controls are available on the Limits tab.

Control Name Description
Minimum Angle Minimum counterclockwise angle at which the edge can be located from a line perpendicular to the search direction.
Maximum Angle Maximum counterclockwise angle at which the edge can be located from a line perpendicular to the search direction.
Maximum Deviation Maximum average error between found edge points and the fitted straight line.
Minimum Short Distance Minimum distance allowed for the shorter of the following distances:
  • The distance between the start point of the first search line and the intersection of the fitted line and the first search line.
  • The distance between the start point of the last search line and the intersection of the fitted line and the last search line.
Maximum Long Distance Maximum distance allowed for the longer of the following distances:
  • The distance between the start point of the first search line and the intersection of the fitted line and the first search line.
  • The distance between the start point of the last search line and the intersection of the fitted line and the last search line.
Step Results Displays information about the straight edge found in the image.
Note  When you calibrate the image using a Calibrate Image step, X and Y are returned in the calibration unit you specified.