fitangle

R2026b

Measure angle in image using angle tool

Since R2026b

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Syntax

measurementData = fitangle(I,position)
measurementData = fitangle(I,position,Name=Value)

Description

measurementData = fitangle(I,position) measures an angle in a grayscale or RGB input image, I, by positioning an angle tool at the position position. This function performs a semi-automatic angle measurement when the tool snaps to linear edges detected near the specified position.

example

measurementData = fitangle(I,position,Name=Value) specifies options using one or more name-value arguments. For example, SnapNeighborhood=10 specifies the snapping neighborhood as 10 pixels.

Examples

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Open Live Script

Read a test image of a metal plate into the workspace.

A = imread("solidplate.png");
A = imadjust(A);
hIm = imageshow(A);

Measure the angle at a specified vertex using the fitangle function.

angleToolVertices = [2215 2166; 2484 1996; 2563 1743];
hAngle = fitangle(A,angleToolVertices)
hAngle = struct with fields:
    Position: [3×2 double]
       Theta: 135.0553

Input Arguments

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Input image in which to perform the angle measurement, specified as one of these values:

Image TypeData Format
Grayscale H-by-W numeric matrix
RGB H-by-W-by-3 numeric array

Note

By default, spatial image coordinates are in the intrinsic coordinate system, where the center of the upper left pixel has intrinsic coordinates (1.0, 1.0). If you perform a coordinate transformation on the image input I, units are defined in the world coordinate system. To learn more, see Image Coordinate Systems.

Angle tool position, in pixels, specified as a 3-by-2 numeric matrix. The rows of the numeric matrix are in the form [x, y] and represent the start point, vertex point, and end point coordinates that define the angle.

Name-Value Arguments

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Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: fitangle(hImage,position,SnapNeighborhood=10) specifies the snapping neighborhood as 10 pixels.

Snap the angle to linear edges, specified as a numeric or logical 1 (true) or 0 (false). By default, the tool snaps the two lines between the start point, vertex point, and end point.

Specify the snap method using the LineSnapMethod argument. Specify the snap neighborhood using the SnapNeighborhood argument.

Snapping neighborhood, specified as a positive integer. The SnapNeighborhood is the perpendicular distance on either side of each angle line segment within which the angle tool searches for linear edges to snap to. Units are in pixels.

To enable automatic snapping of the angle to linear edges, specify the Snap argument as true (or 1).

Method for automatically aligning reference lines to edges, specified as one of these options:

  • "closest" — Snap the reference line to the closest linear edge based on pixel distance from the midpoint of the reference line to the linear edge. Use this method for simple images with well-defined edges.

  • "strongest" — Snap the reference line to the linear edge with the highest Hough accumulator value. Use this method when multiple edges are close together but one is more prominent, or in noisy images where only strong features are of interest.

  • "parallel" — Snap the reference line to the linear edge that has the highest cosine similarity to the reference line. Use this method to snap to the edge that is most parallel to a specified reference line, regardless of its position.

  • "combined" — Snap the reference line to a linear edge based on the combined metrics of the "closest", "strongest", and "parallel" methods.

Edge detection method for snapping, specified as a logical array or one of these options.

MethodDescription
"canny"

Finds edges by looking for local maxima of the gradient of the image. The edge function calculates the gradient using the derivative of a Gaussian filter. This method uses two thresholds to detect strong and weak edges, including weak edges in the output if they are connected to strong edges. By using two thresholds, the Canny method is less likely than the other methods to be fooled by noise, and more likely to detect true weak edges.

"sobel"

Finds edges at those points where the gradient of the image is maximum, using the Sobel approximation to the derivative.

"prewitt"

Finds edges at those points where the gradient of the image is maximum, using the Prewitt approximation to the derivative.

"roberts" Finds edges at those points where the gradient of the image is maximum, using the Roberts approximation to the derivative.
"log" Finds edges by looking for zero-crossings after filtering the image with a Laplacian of Gaussian (LoG) filter.
"zerocross" Finds edges by looking for zero-crossings after filtering the image.
"approxcanny"

Finds edges using an approximate version of the Canny edge detection algorithm that provides faster execution time at the expense of less precise detection.

If you specify EdgeMap as a logical array, you define a binary image that contains precomputed edge locations for snapping. Select this option to avoid repeated edge detection when making multiple measurements on the same image.

Geometric transformation for the input image data that defines a 2-D world coordinate system, specified as an affinetform2d object, an imref2d object, a rigidtform2d object, a simtform2d object, or a transltform2d object.

If you perform a coordinate transformation on the input image data, the units of measurementData are defined in the world coordinate system. To learn more about image coordinate systems, see Image Coordinate Systems.

Output Arguments

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Angle measurement result, returned as a structure with these fields:

measurementData FieldDescription
Theta

Measured angle, stored as a positive numeric scalar.

Position

Position of the angle tool, stored as a 3-by-2 numeric matrix. The rows of the numeric matrix are in the form [x, y] and represent the start point, vertex point, and end point coordinates that define the angle.

Note

Position might not equal the value of the position argument, because the angle tool automatically snaps to linear image edges.

Extended Capabilities

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Version History

Introduced in R2026b

See Also

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