The SoVRMLGeoLOD node allows applications to build massive tiled, multi-resolution terrain models where the viewer progressively loads higher resolution detail as you fly into the terrain.

VRML X3D SPECIFICATION

This section describes the expected behavior of the node in a conforming X3D / VRML97 browser application. In some cases, the application is responsible for implementing portions of the expected behavior. Open Inventor viewer classes and IVF classes implement some of the application behaviors.

This section may reference portions of the X3D specification that are not present in this help file. The complete X3D spec is available at http://www.web3d.org.

The SoVRMLGeoLOD node provides a terrain-specialized form of the LOD node. It is a grouping node that specifies two different levels of detail for an object using a tree structure, where 0 to 4 children can be specified, and also efficiently manages the loading and unloading of these levels of detail. The level of detail is switched depending upon whether the user is closer or further than range meters from the geospatial coordinate center. The center field should be specified as described in 25.2.4 Specifying geospatial coordinates. The geoOrigin field is used to specify a local coordinate frame for extended precision as described in 25.2.5 Dealing with high-precision coordinates. The geoSystem field is used to define the spatial reference frame and is described in 25.2.3 Specifying a spatial reference frame. When the user is outside the specified range, only the geometry for rootUrl or rootNode are displayed. When the viewer enters the specified range, this geometry is replaced with the contents of the four children files defined by child1Url through child4Url. The four children files are loaded into memory only when the user is within the specified range. Similarly, these are unloaded from memory when the user leaves this range. Figure below illustrates this process. The child URLs shall be arranged in the same order as in the figure; i.e., child1Url represents the bottom-left quadtree child. It is valid to specify less than four child URLs; in which case, the SoVRMLGeoLOD should switch to the children nodes when all of the specified URLs have been loaded. This latter feature can support tree structures other than quadtrees, such as binary trees.

The rootUrl and rootNode fields provide two different ways to specify the geometry of the root tile. You may use one or the other. The rootNode field lets you include the geometry for the root tile directly within the X3D file; whereas the rootUrl field lets you specify a URL for a file that contains the geometry. The result of specifying a value for both of these fields is undefined. The children field is used to expose a portion of the scene graph for the currently loaded set of nodes. The value returned as an event is an MFNode containing the currently selected tile. This will either be the node specified by the rootNode field or the nodes specified by the child1Url, child2Url, child3Url, and child4Url fields. The SoVRMLGeoLOD node shall generate a new children output event each time the scene graph is changed (EXAMPLE whenever nodes are loaded or unloaded). When the new children event is generated, the SoVRMLGeoLOD node shall also generate a level_changed event with value 0 or 1, where 0 indicates the rootNode field and 1 indicates the nodes specified by the child1Url, child2Url, child3Url, and child4Url fields. The SoVRMLGeoLOD node may optionally be implemented with support for a cache of the most recent nodes that have been loaded. This cache should be global across all SoVRMLGeoLOD instances in a scene. This will improve performance when navigating large terrain models by avoiding excessive loading and unloading when a user makes small changes in viewpoint.

FILE FORMAT/DEFAULT

VRMLGeoLOD {

metadata	NULL
children	[]
center	0 0 0
child1Url	[]
child2Url	[]
child3Url	[]
child4Url	[]
geoOrigin	NULL
geoSystem	["GD","WE"]
range	10
rootUrl	[]
rootNode	[]
bboxCenter	0 0 0
bboxSize	-1 -1 -1

}

ACTION BEHAVIOR

SoGLRenderAction, SoCallbackAction, SoGetBoundingBoxAction, SoRayPickActionSoGetPrimitiveCountAction

EVENTS

eventIn

SoMFNode	addChildren
SoMFNode	removeChildren
SoMFNode	set_children
SoSFNode	set_metadata

eventOut

SoMFNode	children_changed
SoSFNode	metadata_changed
SoSFNode	level_changed

Obsoletesince Open Inventor 9500 The VRML API is no longer supported. See section http://oivdoc95.vsg3d.com/content/compatibility-notes-4#Deprecation of the Reference Manual.

Reference