Understanding the observer and target

The extent of a 3D view cannot be described as a simple rectangular shape, as is the case for 2D, because the data can be viewed from an oblique 3D angle (see the subsection below for more details). This means that navigation and extents in 3D must be handled in a different manner than in 2D.

ArcGlobe and ArcScene use a camera object to manipulate the visible extent in 3D. The 3D location of the camera is called the observer position. The 3D location to which the camera is oriented is the target position. The observer and target positions can be located anywhere within the 3D view, allowing for great flexibility.

To navigate through a 3D view using the camera object, you must move either the observer, the target, or both. A variety of interactive tools with many combinations of observer-target manipulations are available to assist you. This is discussed more fully in 3D navigation concepts in ArcGlobe and 3D navigation concepts in ArcScene.

The use of a camera object, rather than a rectangular extent, also means that a traditional 2D scale does not apply in 3D. Data viewed from an oblique 3D angle will change scale progressively through the 3D view based on the distance of the data from the observer. Data in the foreground will be at a larger scale than data in the background.

For cases in ArcGlobe when a scale is needed—for example, when using scale-dependent rendering in ArcGlobe—a normalized distance to the globe's surface is used instead of a traditional 2D scale. This value is calculated using the size of the display window and the distance to the surface of the globe and is displayed on the status bar in ArcGlobe. It is important to note that it is not the absolute observer elevation.

3D oblique angles and the visible data extent

The images below demonstrate data viewed from a variety of angles. The same data has been viewed from directly above, from an oblique 3D angle with no terrain, and from an oblique 3D angle with the data draped on a terrain surface. The visible area for each of these views has been represented on the subsequent 2D overview map.

2D view of the data (green outline) 3D oblique view of the data (yellow outline) 3D oblique view of the data with terrain (red outline)

The visible data for each of the above views

As you can see from these shapes, rectangles cannot be used for storing 3D extents. The green outline demonstrates a traditional 2D extent. The yellow outline demonstrates the general shape of a 3D oblique view looking at a flat surface. The spreading of the outline as it moves away from the foreground is caused by the changing scale as the viewing distance increases from the observer. The red outline demonstrates that terrain can hide sections of the data.