The Find Circle edit control provides a graphical user interface to the CogFindCircle vision tool, which runs a series of Caliper tools over a specified, circular region of an image to locate multiple edge points, supplies these edge points to an underlying Fit Circle tool, and ultimately returns the circle that best fits those input points while generating the smallest root mean square (RMSError) error.

The Find Circle edit control allows you to specify the region of the image analyzed, control the number of Calipers used, and view vision tool results. The following figure shows the Find Circle edit control:

The edit control offers the following features:

• A row of control buttons at the top left
• A set of function tabs for specifying a number of Calipers, the shape of the search area, and viewing the fitting results
• An image display window for displaying Find Circle tool images and graphics

You can experiment with the edit control by using QuickBuild to create a CogFindCircle tool. A new CogFindCircle tool appears as shown in the following figure:

The following table describes the function of each button:

Table 1. Control buttons

Button	Description	Function
	Run	Uses the current set of configured Calipers to analyze the image stored in the Current.InputImage buffer to produce a set of input points that are then passed to a Fit Circle tool.
	Electric mode	Toggles electric mode, where the Find Circle tool executes automatically when particular configuration parameters change. In electric mode, a lightning bolt appears next to every electric property.
	Local image display	Opens or closes the local image display window. A Find Circle tool supports the following image buffers: The Current.InputImage buffer contains the current image and the set of Calipers that will search for edges. The LastRun.InputImage buffer contains the results of the Find Circle tool after it fits a circle to the found edge points. The LastRun.RegionData_Caliper<X>, where <X> represents the Caliper number.
	Floating image display	Opens one or more floating image windows, which support the same image buffers as the local image display window
	Open	Opens a VisionPro persistence (.vpp) file that contains a set of saved properties for this vision tool object type. VisionPro reports an error if you try to open a .vpp file for another object type.
	Save	Saves the current properties of the vision tool to a VisionPro persistence (.vpp) file. The edit control allows you to choose between saving the vision tool with or without its image buffers and tool results.
	Save As	Saves the current properties of the vision tool to a new VisionPro persistence (.vpp) file
	Reset	Resets the vision tool to its default state.
	Show Floating Results	Opens a separate results window with the same contents as seen in the Point Results tab
	Show ToolTips	Enables or disables the display of tooltips for individual items in the edit control
	Help	Opens this VisionPro online help file

This section contains the following subsections.

• Caliper
• Expected Circular Arc
• Fitter

Use the Settings tab to configure the Calipers and the expected arc segment this Find Circle tool will use. The following figure shows the default Settings tab:

Use the Caliper section of the Settings tab to shape all the Calipers the Find Circle tool uses to locate edges or edge points.

Table 2. Caliper Controls

Feature	Description
NumCalipers	Controls the number of Calipers to use along the expected arc segment. The tool requires a minimum of three Calipers, although using more allows the tool to generate a better fit. In addition, you should use more than three Calipers if you allow the underlying Fit Circle tool to ignore one or more points while calculating the best fitting circle. To determine which point to ignore, the Fit Circle tool considers all possible subsets and keeps the set that produces the best possible score.
CaliperSearchLength	Controls the amount of image perpendicular to the expected arc segment that each Caliper takes into consideration. You can use the Find Circle graphics to specify a general search length or use this field to enter a precise value. Note: In general, to improve accuracy specify additional calipers rather than increasing the search length. Too long a search length can cause the found point to be shifted toward the center of the circle, as shown below:
CaliperProjectionLength	Controls the amount of image parallel to the expected arc segment that each Caliper takes into consideration. You can use the Find Circle graphics to specify a general projection length or use this field to enter a precise value. Note: If you specify a very small value for the projection length, you may need to reduce the filter half size.
CaliperSearchDirection	Controls the direction in which each Caliper searches for edges or edge pairs. By default, each Caliper starts inside the expected arc length and searches outward.

Use the Expected Circular Arc area of the Settings tab to shape the circular arc on which the Calipers operate.

Use the Fitter section of the Settings tab to configure the number of points to ignore.

Use the Caliper Settings tab to configure how the Calipers perform their image analysis. The following figure shows the default Caliper Settings tab:

Use the Caliper Scoring tab to create a collection of scoring functions for the Calipers to use. The following figure shows the default Caliper Scoring tab:

If the Edge Mode is Single Edge, the following scoring functions are available:

• CogCaliperScorerContrast
• CogCaliperScorerPosition
• CogCaliperScorerPositionNeg

If the Edge Mode is Edge Pair, then these scoring functions are available:

• CogCaliperScorerContrast
• CogCaliperScorerPosition
• CogCaliperScorerPositionNeg
• CogCaliperScorerPositionNorm
• CogCaliperScorerPositionNormNeg
• CogCaliperScorerSizeDiffNorm
• CogCaliperScorerSizeDiffNormAsym
• CogCaliperScorerSizeNorm
• CogCaliperScorerStraddle

Use the following function buttons to manage the scoring functions:

Table 6. Function Buttons

Button	Description
	Add a new scoring function. A menu appears with a list of scoring functions appropriate to the current edge mode. Highlight the function that you want and a new line appears in the list of functions at the bottom of the tab. You can add more than one function of the same type.
	RemoveAt the currently highlighted function in the list of functions at the bottom of the tab. A verification message appears asking you to confirm deletion.
	Move the currently highlighted function up in the list, and updates the index of the function within the collection.
	Move the currently highlighted function down in the list, and updates the index of the function within the collection.

The following table describes the columns of the scoring function list:

This section contains the following subsections.

• Inputs
• Results
• Diagnostics

Use the Graphics tab to control which graphics the Find Circle tool generates and displays. The following figure shows the default Graphics tab:

Check the Show Caliper Regions checkbox to show all Caliper regions in the Current.InputImage buffer.

Display any of the following results in the LastRun.InputImage buffer:

• Show the entire best fit circle.
• Show the best fit circle segment.
• Show the edge points the Fit Circle tool used to calculate the circle.
• Show the edge points the Fit Circle tool ignored to calculate the circle.
• Show the edges found by the Calipers.
• Show the regions used by the Calipers.

Enable any of the following results to generate a LastRun.RegionData_Caliper<X> buffer for each Caliper the tool uses:

• Create projection graphs from all the Calipers.
• Create filtered graphs from all the Calipers.
• Show the location of each edge on each projection graph.

Choose any of the following diagnostic graphics:

• Control whether or not the input image is recorded as part of the diagnostic record, and whether the image is copied to the record or saved in the record as a reference.
• Show the projection region of the image in the LastRun.RegionData_Caliper<X> buffer for each Caliper the tool uses.
• Show the expected arc segment as configured in the Current.InputImage in the LastRun.InputImage buffer.

This section contains the following subsections.

• Circle
• Circular Arc

Use the Results tab to view the results of each execution of the Find Circle tool. The following figure shows the default Results tab:

Use the GetCircle area of the Results tab to view the following results about the circle the tool found:

Use the GetCircularArc area of the Results tab to view the following results about the circular arc found by the tool:

Use the Point Results tab to view information about each edge point the Calipers found. The following figure shows an example Point Results tab:

The tab shows the RMSError error of the fitting operation, while the points grid gives the following information about each point result: