drawpolyline
Create customizable polyline ROI
Description
roi = drawpolylinePolyline ROI object and enables interactive drawing of a
polyline region-of-interest (ROI) on the current axes.
To draw the ROI, position the pointer on the image. The cursor changes to a fleur shape. Click to draw vertices of the polyline and drag to draw the lines between the vertices. To finish the ROI, double-click the mouse button. For more information about using the ROI, including keyboard shortcuts and context menu options, see Tips.
Note
drawpolyline is a convenience function for creating a
Polyline ROI object. If you create the ROI object
directly, calling Polyline, you must call the draw object
function to enable interactive drawing of the ROI. In contrast, the
drawpolyline function creates the ROI object and
calls the draw object function for you. Whichever way you
create the ROI, you use object properties, object functions, and event
notifications to customize its appearance and behavior. For more information
about using these capabilities, see Tips.
roi = drawpolyline(___,Name,Value)
Examples
Create Polyline ROI Interactively
Read an image into the workspace and display it.
imshow(imread('westconcordaerial.png'))
Draw the polyline ROI on the image. Use the 'Color' name-value pair to specify the color of the line.
h = drawpolyline('Color','green');
Decrease the width of the edge of the ROI by setting the 'LineWidth' property.
h.LineWidth = 1;
Create Polygonal ROI Programmatically
Read image into the workspace and display it.
I = imread('baby.jpg');
figure
imshow(I)
Draw a polygonal ROI over the image, using named parameters to specify the location and shape. The example also specifies that the edge of the polygon is a striped.
h = drawpolyline('Position',[500 500;400 600;400 700;500 800;600 800;700 700; 700 600]);
Set Up Listener for Polyline ROI Events
Read an image into the workspace.
I = imread('cameraman.tif'); Display the image.
imshow(I);
Draw a Polyline ROI on the image.
roi = drawpolyline('Color','r');
Set up listeners for ROI moving events. When you move it, the ROI sends notifications of these events and executes the callback function you specify.
addlistener(roi,'MovingROI',@allevents); addlistener(roi,'ROIMoved',@allevents);
The allevents callback function displays the previous position and the current position of the ROI.
function allevents(src,evt) evname = evt.EventName; switch(evname) case{'MovingROI'} disp(['ROI moving previous position: ' mat2str(evt.PreviousPosition)]); disp(['ROI moving current position: ' mat2str(evt.CurrentPosition)]); case{'ROIMoved'} disp(['ROI moved previous position: ' mat2str(evt.PreviousPosition)]); disp(['ROI moved current position: ' mat2str(evt.CurrentPosition)]); end end
Input Arguments
Output Arguments
Tips
The ROI supports the following interactivity, including keyboard shortcuts.
Behavior Keyboard shortcut Make drawn line snap at 15 degree angles. Hold the Shift key while drawing. Finish drawing the ROI. Double-click, which adds a final new vertex at the pointer position.
Right-click, which adds a final new vertex at the pointer position.
Press Enter, which adds a final new vertex at the pointer position..
Cancel drawing the ROI. Press Esc. The function returns a valid ROI object with an empty Positionfield.Add a new vertex to the ROI. Position the pointer over the polygon and double-click. You can also position the pointer over the ROI, right-click, and choose Add Vertex.
Remove a vertex from the ROI. Position the pointer over the ROI, right-click, and choose Delete Vertex.
Remove the most recently added vertex but keep drawing. Press Backspace. The function redraws the line from the previous vertex to the current position of the pointer. You can only back up to the first vertex you drew. Resize (reshape) the ROI. Position pointer over a vertex and then click and drag.
Add a new vertex and then click and drag.
Remove a vertex and the shape of the ROI adjusts.
Move the ROI. Position the pointer over the line, not on a vertex. The pointer changes to the fleur shape. Click and drag the ROI. Delete the ROI. Position the pointer anywhere on the ROI and right-click. Select Delete Polyline from the context menu. You can also delete the ROI using the deleteobject function.The
drawpolylinefunction returns aPolylineROI object. After creation, use these capabilities of the object to customize the appearance and behavior of the ROI.Object properties — ROI objects support properties that modify their appearance or behavior. For example, to change the color of the
roito yellow, set itsColorproperty,roi.Color = 'yellow'.Object functions — ROI objects support a set of object functions that operate on the ROIs. For example, if you want to pause the MATLAB command line after creating an ROI, call the
waitobject function.Event notifications — ROI objects can notify your code when certain events, such as being moved or clicked, happen to the ROI. To receive these notifications, use the
addlistenerobject function to set up listeners for specific events. In the listener, specify an event, such as'ROIMoved', and a callback function that executes when the event occurs. When the ROI notifies your application through the listener, it returns data specific to the event. For example, with the'ROIMoved'event, the ROI object returns its previous position and its current position.
For an example of using event listeners with the
Polylineobject, see Set Up Listener for Polyline ROI Events. For more details about these capabilities, see thePolylineobject documentation.
Compatibility Considerations
See Also
drawassisted | drawcircle | drawcrosshair | drawcuboid | drawellipse | drawfreehand | drawline | drawpoint | drawpolygon | drawrectangle | Polyline