Detect and Fit Oblong Holes

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Description

Use this Step to fit an oblong hole to the oblong-hole-shaped edge detected from the image.

oblong hole demo

Usage Scenario

This step is primarily used for precise measurement of parts, workpieces, or assemblies containing oblong holes, and is common in automotive, machining, and assembly inspection applications.

Basic Concepts

  • Oblong hole

    A hole structure consisting of a rectangular midsection with semicircular ends, widely used in mechanical and automotive parts to allow for sliding or adjustment.

  • Caliper

    In image processing, a virtual measurement tool detects edges within a specified region. Adjusting its count, width, and length affects the accuracy and stability of edge detection.

  • Edge polarity

    It refers to the direction of grayscale change across an edge, e.g., dark-to-light or light-to-dark.

Workflow

The process of configuring this Step is shown below:

workflow

  1. Configure the input. Connect the Step ports in the graphical programming workspace or select the input under Input in the parameter configuration panel.

  2. Complete the ROI Settings.

  3. Set other parameters.

  4. Confirm the output items in the Output section.

  5. Run the Step, and view output.

Input Description

Input item Description

Image

The image used for detecting an oblong-hole-shaped edge.

Alignment Parameter Group

This Step is used to adjust the pose of the ROI synchronously according to the pose transformation of the target object.

Parameter Description

Parameter Description

ROI Settings

You can draw an oblong hole ROI, and the system will extract multiple columns of pixels according to the caliper settings. The detected edge points in each column will be used for oblong hole fitting.

See 2D ROI Settings to learn more about ROI and calipers.

Edge Polarity

This parameter specifies the direction in which the grayscale values change at the edges.

Value list:

  • Dark-to-Bright: Detects edges where grayscale values increase from low to high, corresponding to a visual transition from dark to bright.

  • Bright-to-Dark: Detects edges where grayscale values decrease from high to low, corresponding to a visual transition from bright to dark.

  • Any: No limit on the direction of grayscale value change of the edge. Both types can be detected.

Filter Window Size

Specify the window size to be used when filtering each column of pixels in its direction. Filtering can reduce noise and improve the stability of edge detection results.

Edge Mode

Define the edge types to be retained in edge detection.

Value list: Best, First, Last.

Grayscale Change Threshold

This parameter specifies the minimum grayscale variation between adjacent pixels at the edge of an extracted pixel column required for edge point detection. Setting this parameter value properly can effectively filter out weak edges and noise.

Use Relative Threshold

Once selected, an edge point is detected only if the grayscale variation between adjacent pixels at the edge of a pixel column meets or exceeds the specified percentage of the maximum variation in that column. Once this parameter is selected, set Relative Threshold.

Outlier Fraction

The percentage of outlier points to be removed during oblong hole fitting.

Output Description

Select the output item(s) to add the output port(s) to the Step, and the corresponding data will be output after the Step is run. You can select the output according to the actual measurement requirements.

If you select an expandable output item, you should expand it by clicking ▶, and then set the Lower limit and Upper limit values to determine the acceptable range. If the output value falls within the acceptable range, the measurement item is judged as passing (OK), or else it is judged as failing (NG).
Output item Description

Oblong Hole Pose

The position and orientation of the fitted oblong hole.

Center Points

The geometric center of the fitted oblong hole.

Center X

The X coordinate of the center point of the fitted oblong hole.

Center Y

The Y value of the fitted oblong hole center point.

Minor Axis Length

The fitted oblong hole width, which is the diameters of the semicircles at both ends of the oblong hole.

Major Axis Length

The total length of the fitted oblong hole is equal to the distance between the centers of the semicircles at the ends of the oblong hole (i.e., the length of the middle rectangle) plus the radii of the two semicircles.

Oblong Hole Rotation Angle

The rotation angle of the fitted oblong hole, relative to the positive X-axis direction.

Fit Oblong Hole

The fitted oblong hole.

Troubleshooting

For common errors, see Error Code List.

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