### Circle Measure Tool Advanced Parameters

See the Circle Measure Tool Parameters section for details.

- Scan Direction: Sets the direction of the vector edge search, either from the inside out or from the outside in.

- Number of Vectors: This is the number of vectors that will be used to search for gradient points around the edge of the circle. These vectors will be equally spaced and arranged in a radial pattern.

- Edge Strength: Similar to the Width and Height measurements, a gradient plot editor is provided for setting the minimum edge strength of the vectors. With a Width Measurement, the gradient plot is down the middle of the region of interest, moving from left to right. With a Height measurement, the gradient plot is also down the middle of the region of interest, but moving from top to bottom. With Circle measurement, it is selectable. Note that there is a control on the right that allows you select where the gradient scan is taken within the Circle measurement. If lighting around a given circle is uneven, this allows you to see the gradient values on the left, right, top, and bottom edges of the circle. (Range: 0 to 255)

- Polarity: Allows you to determine whether the vectors will search for light to dark edge transitions, dark to light, or both.

- Sharpness: Configures the number of pixels over which the gradient will be calculated. Select a lower value when you have very sharp edges, and select a larger value when your edges are more blurry.

- Edge Point Selection: By default, the Circle Fit tool will use the highest-strength edge. This parameter allows you to choose which transition or line along the vector to select.

  [First (Default)]: The first transition or line meeting the Gradient Threshold requirement along the direction of the vector is output as the result.
  [Best]: The result corresponds to the transition with the highest gradient. This option is not available when Result Type is set to Lines.
  [Last]: The result corresponds to the last qualifying transition or line.
  [Nth]: The result corresponds to the Nth transition or line along the direction of the vector.
  [All]: All qualified transitions or lines are shown on the display and included in the Point List output.

- Minimum Required Edge Points: Allow you to select the minimum number of vector edge points required for a valid circle fit. (Range: 3 to 2,147,483,647)

- Circle Fit Precision: Allow you to choose how precise that fit must be.
  [+/- 0.10 Extra Close Fit]: Only use edge points that are within +/- 0.10 pixels of the circumference and discard the rest.
  [+/- 0.25 Very Close Fit]: Only use edge points that are within +/- 0.25 pixels of the circumference and discard the rest.
  [+/- 0.75 Close Fit]: Only use edge points that are within +/- 0.75 pixels of the circumference and discard the rest.
  [+/- 1.25 Medium/Close Fit]: Only use edge points that are within +/- 1.25 pixels of the circumference and discard the rest.
  [+/- 1.75 Medium Fit]: Only use edge points that are within +/- 1.75 pixels of the circumference and discard the rest.
  [+/- 2.25 Meidum/Rough Fit]: Only use edge points that are within +/- 2.25 pixels of the circumference and discard the rest.
  [+/- 2.75 Rough Fit]: Only use edge points that are within +/- 2.75 pixels of the circumference and discard the rest.
  [+/- 7.75 Very Rough Fit]: Only use edge points that are within +/- 7.75 pixels of the circumference and discard the rest.

- Lower/Upper Tolerance: Set the tolerance on the radius of the circle. (Range: 0 to 100,000)

- Result Type specifies the type of output and provides a choice between Transitions and Lines:
  [Transitions (Default)]: The output point will correspond to the location of the selected gradient transition.
  [Lines]: The output point will correspond to the midpoint between a pair of matched transitions.

- Maximum number of Transitions: Specifies the maximum number of edge points to detect along the edge detection direction.

- Graphics Level: Select graphic display conditions.
  [Show None]: Graphically displays only circles detected as measurement results.
  [Show ROI Only]: Displays the circle detected as the measurement result and the circumscribed rectangle of the circle area to be measured.
  [Show Basic Graphics]: Graphically displays circles and edge points detected as measurement results.
  [Show Details]: Graphically displays circles, edge points, and vector information detected as measurement results.
  [Show Details And Mask]: Mask information is displayed together with the above detailed information.

- Enable Radius and Location Filter: Only points that are within the settings of these parameters will be used as inputs to the circle fit.

- Circle Fit Method: Select a circle fitting method.
  [Normal]: Standard fitting method.
  [Alternate 1]: Use when the variation of edge points is large.

- Circle Range Method: Select how to calculate the region where the circle may exist.
  [3 Point Groups]: Divide the edge point data into 3 groups, calculate one representative point from each group, and calculate an approximate circle from the three representative points. Calculate the range from the mean and variance of the center and radius of this approximate circle.
  [Classic]: Calculates the range from the variance of each edge point.

- Circle Completeness: Set where points on the circle have to be located for circle fit to be generated.
  [Don’t Care]: As long as the minimum number of points are found, the circle fit will be generated.
  [Quadrants]: As long as there are valid points in all four quadrants, the circle fit will be generated.