The Level Of Detail (LOD) plug-in is a mechanism for controlling the level of complexity of a 3D object, depending on camera position and object size. As an object becomes smaller on the screen, the objects polygons become smaller. At a certain size, those polygons are small enough to be replaced by a lower number of larger polygons, without loosing realism. The goal is to maintain the overall shape of the object so it does not change significantly, when the number of polygons are changing.

Viz Artist has a built-in LOD mechanism for text objects and internal objects, such as Sphere, Cylinder and so on. This mechanism changes the tessellation of the object, based on its size on screen. However, there is no LOD mechanism for imported objects and models. This is where the LOD plug-in can be used. The LOD plug-in enables switching between different representations (levels) of the same object, based on its distance from the camera and on the zoom level of the camera. A switching range is assigned to each representation to determine the specific distance from camera n which it is replaced by the next representation.

Additionally, the zoom of the camera is taken into consideration; objects that are far away from the camera appear closer (and larger) at a narrow zoom position, or smaller at wide zoom. To accommodate for different zoom values, LOD assumes that the switching ranges are correlative to a reference zoom value. When the actual zoom value differs from the reference zoom value, the switching ranges are automatically adjusted.

To use LOD on an object, you have to import several representations of that object from an external source. The different representations of the object have to be placed under a group node, in the order of detail, this means the most detailed level is on the top of the group. When LOD is placed on the group container it makes only one of its children (levels) visible at a given time, based on the distance between the center of the object and the camera, as well as the current zoom value, and other selectable parameters of the plug-in.

LOD works in conjunction with LOD Manager that controls all the LOD plug-ins in the scene.

LOD Properties

• Lock: Disables distance switching. In certain cases, it is desirable to disable the distance switching and lock LOD to show one of the levels.

• Lock On Index: Shows index of the selected level when Lock is On.

• Center: Defines whether the distance from the camera is measured from the origin of the object (Automatic) or from a specific point in the object, for example one of the corners (Manual)

• Center X, Y, and Z: Sets the point from which the distance from the camera is measured (in object coordinates), if the Center parameter is set to Manual.

• Range Scale: Sets a scale factor on the switching ranges. This scale factor allows shortening or lengthening the distance at which object representations are switched.

• Range 0: Sets the switching ranges. Those are the distances at which object representations are switched. The number of entries is n+1 where n is the number of children in the group on which LOD is assigned

• Initialize: Re-initializes the LOD plug-in. This is required if the number of children of the LOD group has changed after LOD was assigned to the group.

See Also

• LOD Manager