vtkImagePlaneWidget

Section: Visualization Toolkit Widget Classes

Usage

This 3D widget defines a plane that can be interactively placed in an image volume. A nice feature of the object is that the vtkImagePlaneWidget, like any 3D widget, will work with the current interactor style. That is, if vtkImagePlaneWidget does not handle an event, then all other registered observers (including the interactor style) have an opportunity to process the event. Otherwise, the vtkImagePlaneWidget will terminate the processing of the event that it handles.

The core functionality of the widget is provided by a vtkImageReslice object which passes its output onto a texture mapping pipeline for fast slicing through volumetric data. See the key methods: GenerateTexturePlane() and UpdatePlane() for implementation details.

To use this object, just invoke SetInteractor() with the argument of the method a vtkRenderWindowInteractor. You may also wish to invoke "PlaceWidget()" to initially position the widget. If the "i" key (for "interactor") is pressed, the vtkImagePlaneWidget will appear. (See superclass documentation for information about changing this behavior.)

Selecting the widget with the middle mouse button with and without holding the shift or control keys enables complex reslicing capablilites. To facilitate use, a set of 'margins' (left, right, top, bottom) are shown as a set of plane-axes aligned lines, the properties of which can be changed as a group. Without keyboard modifiers: selecting in the middle of the margins enables translation of the plane along its normal. Selecting one of the corners within the margins enables spinning around the plane's normal at its center. Selecting within a margin allows rotating about the center of the plane around an axis aligned with the margin (i.e., selecting left margin enables rotating around the plane's local y-prime axis). With control key modifier: margin selection enables edge translation (i.e., a constrained form of scaling). Selecting within the margins enables translation of the entire plane. With shift key modifier: uniform plane scaling is enabled. Moving the mouse up enlarges the plane while downward movement shrinks it.

Window-level is achieved by using the right mouse button. Window-level values can be reset by shift + 'r' or control + 'r' while regular reset camera is maintained with 'r' or 'R'. The left mouse button can be used to query the underlying image data with a snap-to cross-hair cursor. Currently, the nearest point in the input image data to the mouse cursor generates the cross-hairs. With oblique slicing, this behaviour may appear unsatisfactory. Text display of window-level and image coordinates/data values are provided by a text actor/mapper pair.

Events that occur outside of the widget (i.e., no part of the widget is picked) are propagated to any other registered obsevers (such as the interaction style). Turn off the widget by pressing the "i" key again (or invoke the Off() method). To support interactive manipulation of objects, this class invokes the events StartInteractionEvent, InteractionEvent, and EndInteractionEvent as well as StartWindowLevelEvent, WindowLevelEvent, EndWindowLevelEvent and ResetWindowLevelEvent.

The vtkImagePlaneWidget has several methods that can be used in conjunction with other VTK objects. The GetPolyData() method can be used to get the polygonal representation of the plane and can be used as input for other VTK objects. Typical usage of the widget is to make use of the StartInteractionEvent, InteractionEvent, and EndInteractionEvent events. The InteractionEvent is called on mouse motion; the other two events are called on button down and button up (either left or right button).

Some additional features of this class include the ability to control the properties of the widget. You can set the properties of: the selected and unselected representations of the plane's outline; the text actor via its vtkTextProperty; the cross-hair cursor. In addition there are methods to constrain the plane so that it is aligned along the x-y-z axes. Finally, one can specify the degree of interpolation (vtkImageReslice): nearest neighbour, linear, and cubic.

To create an instance of class vtkImagePlaneWidget, simply invoke its constructor as follows

  obj = vtkImagePlaneWidget

Methods

The class vtkImagePlaneWidget has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkImagePlaneWidget class.