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Procedure for using the CircleFinder step


The following procedure provides a basic methodology for using the CircleFinder step:

  1. Define a circle model.

  2. Optionally, adjust the CircleFinder step settings to control the search.

  3. Run the project to the CircleFinder step to ensure your project works correctly.

Define a circle model

To define a circle model, perform the following:

  1. Click on the Define circle () toolbar button in the Project toolbar.

  2. On the image, click and hold in the center of the circular shape that you are defining; then, drag outwards to the required radius. Alternately, set the Radius in the Configuration pane.

  3. Confirm or cancel the defined shape in the Circle control panel ( ).

    To redefine the circle, click the Redefine shape button in the Configuration pane.

CircleFinder step settings

The CircleFinder step settings control the search. Typically, the default settings are sufficient; however you can specify other values if necessary. To change the default CircleFinder step settings, perform one or more of the following:

  1. Set the Total number of occurrences, Smoothness, Detail level, Acceptance, and Polarity. Use these, and other Search settings available for all Finder steps, to further control edge extraction and the definition and identification of a match.

  2. Set the Fit score min. Use this to guarantee a certain quality of fit. The fit score is a measure of the correlation of the edges in your model to those in the occurrence. It is equal to [1 - Normalized Fit Error]. A perfect fit gives a fit score of 100.0. The fit error is calculated the same way as in the ModelFinder step. For more information on fit error, see the Fit error subsection of the Determining what is a match section in Chapter 13: ModelFinder step.

  3. Set the Sagitta tolerance. Use this to find deformed circular shapes; set this to the allowable radial deviation tolerance. See the Sagitta tolerance section later in this chapter for more information.

  4. Set the Coverage max. Use this to locate an arc instead of a full circle; specify the expected occurrence contour percentage that will be visible in your image. The default value is 100%.