3.1.6 Viewer Window

The 3D viewer plays a central role in Amira. Here all geometric objects are shown in 3D space. The 3D viewer offers powerful and fast interaction techniques. It can be regarded as a virtual camera which can be moved to an arbitrary position within the 3D scene. The left mouse button is used to change the view direction by means of a virtual trackball. The middle mouse button is used for panning, while the left and the middle mouse button pressed together allow you to zoom objects.

Sometimes you need to manipulate objects directly in the 3D viewer. For example, this technique, called 3D interaction, is used by the transform editor. The editor provides special draggers that can be picked and translated or rotated in order to specify the transformation of a data object. Before you can interact with these draggers, you must switch the viewer into interaction mode. This is done by clicking on the arrow button in the upper right corner. If the viewer is in interaction mode, the mouse cursor will be an arrow instead of a hand symbol. You can use the [ESC] key in order to quickly switch between interaction mode and viewing mode. If the viewer is in interaction mode, use the [Alt] key to temporarily switch to viewing mode.

Figure 31: Amira's viewer window provides a virtual trackball for easy navigation. The decoration frame contains several controls, allowing you for example to switch between viewing mode and interaction mode, to choose certain orienations, or to take snapshots.

More than one viewer can be active at a time. Standard screen layouts with one, two, or four viewers can be selected via the view menu. Additional viewers can be created using the Tcl command viewer <n> show, where <n> is an integer number between 0 and 15. While viewers 0 to 3 will be placed in a common panel window, viewers 4 to 15 will create their own top-level window. For more specific control, the viewer provides an extensive command set, which is documented below.

The decoration of the viewer window provides several buttons and controls, see Figure 31. The precise meaning of these controls is described below.

Edit Background Color: Pops up a color editor which allows you to change the main background color of the viewer. In order to change the secondary background color which is used if a non-uniform background pattern has been selected, use the Swap colors option of the main winodw's View Background menu (see Section 3.1.3). Alternatively, you may use the viewer command setBackgroundColor2.
Snapshot: Takes a snapshot of the current rendering area and saves it in a file. The filename as well as the desired output format have to be entered through the snapshot dialog. Snapshots may also be taken using the viewer command snapshot.
Seek: Pressing the seek button and then clicking on an arbitrary object in the scene causes the object to be moved into the center of the viewer window. Moreover, the camera will be oriented parallel to the normal direction at the selected point. Seeking mode may also be activated by pressing the [S] key in the viewer window.
Animate Camera: If this button is pressed, the first camera path object found in the Object Pool will be used for animation. No action is performed if no camera path is found. In order to create a camera path, select KeyframeCamPath from the Edit Create menu and invoke the camera path editor.
Pick: Switches the viewer into interaction mode. You can also use the [ESC] key to toggle between viewing mode and interaction mode.
View: Switches the viewer into viewing mode. You can also use the [ESC] key to toggle between interaction mode and viewing mode.
Home: Resets camera to the home position.
Set Home: Sets the current position as the new home position.
View All: Repositions the camera so that all objects become visible. The orientation of the camera will not be changed.
Perspective/Ortho: Toggles between a perspective and an orthographic camera. By default, a perspective camera is used. You may want to use an orthographic camera in order to measure distances or to exactly align objects in 3D space.
YZ-, XZ- and XY-Views: Adjusts the camera according to the specified viewing direction. The viewing direction is parallel to the coordinate axis perpendicular to the specified coordinate plane. Medical doctors are used to viewing series of tomographic images parallel to the XY-plane with the y-axis pointing downwards. This convention is followed by the XY-button. The opposite view direction is used if the Shift key is pressed.
Rotate: Rotates the camera around the current view direction. By default, a clockwise rotation of one degree is performed. If the Shift-key is pressed while clicking, a 90 degree rotation is done. If the Ctrl-key is pressed, the rotation will be counterclockwise.

In addition to theses buttons the Amira viewers provide an extensive set of Tcl commands, which are listed in the next section.

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