Creating Your Own Modular Tools

Creating Your Own Modular Tools

In this section...

“Overview” on page 5-33

“Create Angle Measurement Tool” on page 5-35

Overview

Because the toolbox uses an open architecture for the modular interactive tools, you can extend the toolbox by creating your own modular interactive tools, using standard Handle Graphics concepts and techniques. To help you create tools that integrate well with the existing modular interactive tools, the toolbox includes many utility functions that perform commonly needed tasks.

The utility functions can help check the input arguments to your tool, add callback functions to a callback list or remove them from a list, and align figure windows in relation to a fixed window. The toolbox also provides a set of functions that you can use to define a region-of-interest of various shapes, including points, lines, rectangles, ellipses, polygons, and freehand shapes — see “Create Angle Measurement Tool” on page 5-35 for more information.

The following table lists these utility functions in alphabetical order. See the function’s reference page for more detailed information.

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Create Angle Measurement Tool

The toolbox includes a set of functions that you can use to enable users of your image processing GUI to define a region-of-interest (ROI) on the target image. The functions implement drawing of various shapes of ROI, such as rectangles, ellipses, and polygons, and returning information about the

coordinates that define the ROI. These ROI objects support methods that you can use to control aspects of its appearance and behavior.

To illustrate how to use these ROI tools, this example creates a simple angle measurement tool This custom tool uses impoly to create a two-segment polyline on an image and displays the angle created by the two line segments in a title in the figure. Users of the tool can move the polyline anywhere on the image and view the angle formed by the two line segments.

function my_angle_measurement_tool(im)

%Create figure, setting up properties figure('Name','My Angle Measurement Tool',...

'NumberTitle','off',...

'IntegerHandle','off');

%Display image in the axes

imshow(im)

%Get size of image. m = size(im,1);

n = size(im,2);

%Get center point of image for initial positioning. midy = ceil(m/2);

midx = ceil(n/2);

%Position first point vertically above the middle. firstx = midx;

firsty = midy - ceil(m/4); lastx = midx + ceil(n/4); lasty = midy;

%Create a two-segment right-angle polyline centered in the image.

h = impoly(gca,[firstx,firsty;midx,midy;lastx,lasty],'Closed',false); api = iptgetapi(h);

initial_position = api.getPosition()

%Display initial position updateAngle(initial_position)

%set up callback to update angle in title. api.addNewPositionCallback(@updateAngle);

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fcn = makeConstrainToRectFcn('impoly',get(gca,'XLim'),get(gca,'YLim')); api.setPositionConstraintFcn(fcn);

%

%Callback function that calculates the angle and updates the title.

%Function receives an array containing the current x,y position of

%the three vertices.

function updateAngle(p)

%Create two vectors from the vertices.

%v1 = [x1 - x2, y1 - y2]

%v2 = [x3 - x2, Y3 - y2]

v1 = [p(1,1)-p(2,1), p(1,2)-p(2,2)];

v2 = [p(3,1)-p(2,1), p(3,2)-p(2,2)]; % Find the angle.

theta = acos(dot(v1,v2)/(norm(v1)*norm(v2))); % Convert it to degrees.

angle_degrees = (theta * (180/pi));

% Display the angle in the title of the figure. title(sprintf('(%1.0f) degrees',angle_degrees))

To use the angle measurement tool, pass it an image.

I = imread('gantrycrane.png'); my_angle_measurement_tool(I);

The tool opens a figure window, displaying the image with the angle measure tool centered over the image in a right angle. Move the pointer over any of the vertices of the tool to measure any angle in the image. In the following figure, the tool is measuring an angle in the image. Note the size of the angle displayed in the title of the figure.

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Angle displayed

in title.

Angle measurement

tool

Custom Angle Measurement Tool

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