The PlaneView3D Applet Interface

The interface of PlaneView3D provides multiple interactive features. One of the key features of the interface design is the inclusion of controls for displaying different views of an object by either changing the position of the camera or the position of the 3D object in relation to the camera (see Figure 3 for the PlaneView3D interface design). This tool differs from previous visualization aids by allowing users to choose from a list of the most commonly described projection types including multiview, axonometric, oblique, and perspective. Due to the number of required controls and the space required for each control, the applet is best fully viewed with a 17" or larger monitor set at 640 X 480 resolution. When viewing the applet with a 15' or smaller monitor, an 800 X 600 resolution setting will enable the applet to fit within the screen.

Figure 3 The PlaneView3D Applet Interface.

PlaneView3D Interactive Features

The canvas areas shown in Figure 4 are used for representing the world and view reference coordinate systems. Figure 4a shows a three-dimensional view of a barn in the world coordinate system. Within this canvas, the 3D object is shown in relation to the x-, y-, z-axes forming the world coordinate system. Since it is difficult to determine the size of the object and the x-, y-, and z-coordinates for the endpoints forming the 3D object, one of the points of the object is labeled as "1" (see Figure 4a). The coordinate positions of this point as well as the width, height, and length of the object are given in a Message Box shown in Figure 3. By giving the position of this point and the object's dimensions, the location of the View Reference Point (VRP) can be more accurately set.

The second canvas represents the view reference coordinate system (see Figure 4b). This canvas displays the object using the desired projection type. As with the projection of the object in the world coordinate system, axes are shown in relation to the object for all views with the exception of multiview projections. Often an object displayed in this canvas can appear distorted or difficult to interpret due to the inclusion of hidden lines. To remove hidden lines from the object displayed in the viewing reference coordinate system, check the Remove Hidden Lines checkbox shown in Figure 3.

Figure 4 Canvases representing the a) world coordinate system; and b) view reference coordinate system.

After loading the applet to the browser, the Barn building is drawn inside of the world coordinate system canvas. Additional objects such as a Cube or Pyramid can be selected from the Projected Shape choice box (see Figure 3). Modifications can then be made to the object through sliders located on the right side of the applet (see Figures 3 and 5a). Sliders within this section enable the object to be translated, scaled, or rotated in the world coordinate view canvas.

Figure 5 Control panels for a) repositioning the 3D object in the world coordinate system; and b) establishing the view reference coordinate system.

Repositioning of the camera or the viewing position can be achieved by VRP sliders located at the top of the control panel shown in Figure 5b. As described in the Planar Geometric Projections Tutorial , the VRP sets the origin of the view reference coordinate system. A Show VRP Position checkbox located at the top of the applet (see Figure 3) can be selected to show its position in reference to the world coordinate view system. The displayed position of the VRP in this canvas can be misleading because multiple points defined with x-, y-, and z-coordinates project to the same location on a two-dimensional plane. For a more accurate depiction of the VRP location, the user should refer to the Message Box for the x-, y-, and z-coordinates corresponding to an endpoint of the object. Using the location of this endpoint in combination with the width, height, and length of the object (also found in the Message Box), the position of the VRP can be accurately determined in relation to the 3D object. After establishing the location of the origin of the view reference coordinate system, the Viewplane Normal (VPN) and Upward Vector (VUP) sliders (shown in Figure 5b) define the location of the viewplane.

The Projection Type choice box contains 10 commonly discussed subclasses of planar geometric projections (see Figure 3 for the location of the Projection type choice box). Major subdivisions of planar geometric projections are listed consecutively as multiview, axonometric, oblique, and perspective projections. Multiview projections available from this selection tool include a planar or top view, a front view, and a side view. Axonometric projections, listed next within the Projection Type choice box, are divided into isometric, dimetric, and trimetric projections. Cabinet and cavalier projections comprise the oblique projection type while one-point and two-point perspective projections are included in the final group.

Oblique and perspective projections require the availability of additional parameter settings. To provide a user-friendly interface, the controls for these parameters are only available with the selection of their respective projection type. The default layout is displayed when the user has selected either a multiview or axonometric projection. In this panel (shown in Figure 6a) the layout contains only a Display Projection button. In the case of an oblique projection, the panel (shown in Figure 6b) includes additional radio buttons for setting the angle theta described in the Planar Geometric Projections Tutorial. For the selection of one- and two-point perspective projections, the layout changes to the panel shown in Figure 6c. In addition to the Display Projection button, this panel contains the Eye Position sliders which define the distance between the eye and the VRP.

Figure 6 Interchangeable control panels for a) multiview and axonometric projections; b) oblique projections; and c) perspective projections.