Polyline

Polyline region of interest

Description

The Polyline object is a polyline region-of-interest (ROI).

To draw the ROI, position the cursor on the axes and click and drag to create the shape. As you draw, click to place vertices along the line. Double-click to finish drawing the polyline. For more information about using this ROI, including keyboard shortcuts, see Tips.

Creation

Description

To create a Polyline object, use the images.roi.Polyline creation function. After creating the object, call the draw object function to begin drawing. As a convenience, you can also use the drawpolyline function to create a Polyline ROI. The drawpolyline function creates the ROI object and automatically calls the draw object function.

roi = images.roi.Polyline creates an instance of the images.roi.Polyline class with default properties.

roi = images.roi.Polyline(ax,___) creates the ROI in the axes specified by ax.

roi = images.roi.Polyline(___,Name,Value) sets properties using name-value pairs. For example, images.roi.Polyline('Color','y') sets the color of the Polyline object to yellow. You can specify multiple name-value pairs. Enclose each property name in single quotes.

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

Parent of ROI, specified as an Axes object or a UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

Properties

Color — ROI color

blue (default) | ColorSpec

ROI color, specified as a MATLAB^® ColorSpec (Color Specification).

Example: 'green'

Example: 'g'

Example: [0 1 0]

ContextMenu — Context menu

ContextMenu object

Context menu, specified as a ContextMenu object. Use this property to display a custom context menu when you right-click the ROI. You can create a custom context menu by using the uicontextmenu function and then configuring context menu properties.

Deletable — ROI can be interactively deleted via context menu

true (default) | false

ROI can be interactively deleted via a context menu, specified as true or false. When the value is true (default), you can delete the ROI via the context menu. To disable this context menu item, set this property to false. When the value is set to false, you can still delete the ROI by calling the delete function specifying the handle to the ROI as the input.

DrawingArea — Area of axes in which you can interactively place ROI

'auto' (default) | 'unlimited' | [x,y,w,h]

Area of the axes in which you can interactively place the ROI, specified as one of the values in this table.

Value	Description
'auto'	The drawing area is the current axes limits (default).
'unlimited'	The drawing area has no boundary and ROIs can be drawn or dragged to extend beyond the axes limits.
[x,y,w,h]	The drawing area is restricted to a rectangular region beginning at (x,y), and extending to width w and height h.

HandleVisibility — Visibility of ROI handle in Children property of parent

'on' (default) | 'off' | 'callback'

Visibility of the ROI handle in the Children property of the parent, specified as one of the values in this table.

Value	Description
'on'	The object handle is always visible (default).
'off'	The object handle is hidden at all times.
'callback'	The object handle is visible from within callbacks or functions invoked by callbacks, but not from within functions invoked from the command line.

InteractionsAllowed — Interactivity of ROI

'all' (default) | 'none' | 'reshape' | 'translate'

Interactivity of the ROI, specified as one of the values in this table.

Value	Description
'all'	The ROI is fully interactable (default).
'none'	The ROI is not interactable, and no drag points are visible.
'translate'	The ROI can be translated (moved) within the drawing area but not reshaped.
'reshape'	The ROI can be reshaped but not translated.

Label — ROI label

'' (default) | character vector | string

ROI label, specified as a character vector or string. By default, the ROI has no label ('').

LabelVisible — Visibility of ROI label

'on' (default) | 'off' | 'hover'

Visibility of the ROI label, specified as one of these values:

Value	Description
'on'	Label is visible when the ROI is visible and the Label property is nonempty (default).
'hover'	Label is visible only when the mouse hovers over the ROI.
'off'	Label is not visible.

LineWidth — Width of ROI edge

three times the number of points per screen pixel (default) | positive numeric scalar

Width of the ROI edge, specified as a positive numeric scalar in points. The default value is three times the number of points per screen pixel.

Parent — ROI parent

Axes object | UIAxes object

ROI parent, specified as an Axes or UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

Position — Position of ROI

[] (default) | n-by-2 numeric array

Position of ROI, specified as a n-by-2 array of the form [x1 y1; x2 y2], where n is the total number of vertices. Each row specifies the respective end-point of a line segment. Polyline generates these points as you draw the ROI shape interactively. To work with fewer points, use the reduce object function.

Selected — Selection state of ROI

false (default) | true

Selection state of the ROI, specified as the logical value true or false. You can also set this property interactively. For example, clicking on the ROI selects the ROI and sets this property to true. Similarly, pressing the Ctrl key and clicking the ROI deselects the ROI and sets the value of this property to false.

SelectedColor — Color of ROI when selected

'none' (default) | ColorSpec

Color of the ROI when selected, specified as a MATLAB ColorSpec (Color Specification). The intensities must be in the range [0,1]. If 'SelectedColor' is set to 'none', then the value of Color defines the color of the ROI for all states, selected or not.

Example: 'green'

Example: 'g'

Example: [0 1 0]

StripeColor — Color of ROI stripe

'none' (default) | ColorSpec value

Color of the ROI stripe, specified as a MATLAB ColorSpec (Color Specification) value. By default, the edge of an ROI is solid colored. If you specify StripeColor, the ROI edge is striped. The striping consists of a combination of the value specified by 'Color' and this value.

Example: 'green'

Example: 'g'

Example: [0 1 0]

Tag — Tag to associate with the ROI

'' (default) | character vector | string scalar

Tag to associate with the ROI, specified as a character vector or string. Use the tag value to find the ROI object in a hierarchy of objects using the findobj function.

UserData — Data to associate with ROI

any MATLAB data

Data to associate with the ROI, specified as any MATLAB data. For example, you can specify a scalar, vector, matrix, cell array, string, character array, table, or structure. MATLAB does not use this data.

Visible — ROI visibility

'on' (default) | 'off' | on/off logical value

ROI visibility, specified as 'on' or 'off', or as numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. Thus, you can use the value of this property as a logical value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState.

Value	Description
'on'	Display the ROI (default).
'off'	Hide the ROI without deleting it. You still can access the properties of an invisible ROI.

Object Functions

addlistener	Create event listener bound to event source
beginDrawingFromPoint	Begin drawing ROI from specified point
bringToFront	Bring ROI to front of Axes stacking order
createMask	Create binary mask image from ROI
draw	Begin drawing ROI interactively
reduce	Reduce density of points in ROI
wait	Block MATLAB command line until ROI operation is finished

Examples

Create Polyline ROI Non-interactively

Read an image into the workspace and display it.

I = imread('baby.jpg');
figure;
imshow(I)

Create a polyline ROI on the image, using properties to specify the location of vertices. For programmatically created ROIs, if you want the ROI drawn in a specific axes, you must specify that axes as an input argument. Otherwise, an instance of the images.roi.Polyline class is created but not displayed. In this example, specify the current axes (gca) to draw the ROI on the image in that axes.

h = images.roi.Polyline(gca,'Position',[100 150; 200 250; 300 350; 150 450]);

Set Up Listeners 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. Because this example specifies the length and location of the ROI, you do not have to call the draw method to enable interactive drawing.

roi = images.roi.Polyline(gca,'Position',[115 30; 80 45; 80 80; 115 90; 145 65]);

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 at the command line 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

More About

Events

To receive notification from the ROI when certain events happen, set up listeners for these events. You can specify a callback function that executes when one of these events occurs. When the ROI notifies your application through the listener, it returns data specific to the event. Look at the event class for the specific event to see what is returned.

For an example, see Set Up Listeners for Polyline ROI Events.

Event Name	Trigger	Event Data	Event Attributes
DeletingROI	ROI is about to be interactively deleted.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingStarted	ROI is about to be interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingFinished	ROI has been interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
MovingROI	ROI shape or location is being interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIMoved	ROI shape or location has been interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIClicked	ROI has been clicked.	images.roi.ROIClickedEventData	NotifyAccess: private ListenAccess: public
AddingVertex	A vertex is about to be interactively added to the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
VertexAdded	A vertex has been interactively added to the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
DeletingVertex	A vertex is about to be interactively deleted from the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
VertexDeleted	A vertex has been interactively deleted from the ROI.	event.EventData	NotifyAccess: private ListenAccess: public

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 Position field.
  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 polygon.
  Delete the ROI.	Position the pointer over the line, right-click, and select Delete Polyline from the context menu. You can also delete the ROI programmatically using the delete object function.

• For information about using an ROI in an app created with App Designer, see Using ROIs in Apps Created with App Designer.

Compatibility Considerations

UIContextMenu property is not recommended

Not recommended starting in R2020a

Starting in R2020a, using the UIContextMenu property to assign a context menu to a graphics object or UI component is not recommended. Use the ContextMenu property instead. The property values are the same.

There are no plans to remove support for the UIContextMenu property at this time. However, the UIContextMenu property no longer appears in the list returned by calling the get function on a graphics object or UI component.