XdkWrl: GeoLOD Class Reference

6.26 GeoLOD

The GeoLOD 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 metres from the geospatial coordinate that is defined by the field center. The format of the center field is described in 4.15.4, Encoding geospatial coordinates.

The geoOrigin field is used to specify a local coordinate frame for extended precision as described in 4.15.5 Dealing with high-precision coordinates.

The geoSystem field is used to define the spatial reference frame and is described in 4.15.3, Encoding 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 6.9 illustrates this process. Note however that there is no requirement that the child URLs be arranged in the same order as in the figure, i.e. child1Url does not need to represent the bottom-left quadtree child. Note also that it is valid to specify less than 4 child URLs, in which case the GeoLOD 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.

Figure 6.x -- Illustrating the GeoLOD level of detail transition

The rootUrl and rootNode fields provide two different ways to specify the geometry of the root tile. The rootNode field may be used to include the geometry for the root tile directly within the VRML file; whereas the rootUrl field specifies a URL for a file that contains the geometry. The result of specifying a value for both of these fields is undefined.

The children eventOut is used to expose the scene graph for the currently loaded set of nodes. The value returned is an MFNode with a single Switch node. This Switch node contains the root nodes in the first node of the choice field, and all the currently loaded children nodes in the second node of the choice field. The whichChoice field of the Switch node determines whether the root (0) or the children nodes (1) are being displayed. The GeoLOD node will generate a new children eventOut every time the scene graph is changed (e.g., whenever nodes are loaded or unloaded).

The GeoLOD node may be implemented with support for a cache of the most recent nodes that have been loaded. This cache should be global across all GeoLOD 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.

Constructor & Destructor Documentation

GeoLOD ( const char * name = "" )

Construct a node with all its fields set to default value, which is equivalent to the code below:

  center = string("");
  
  range = 10;

Member Function Documentation

wrl::Node * duplicate ( std::map< const Node *, Node * > & ) const [virtual]

Implements Node.

wrl::Node * duplicate ( ) const [virtual]

Returns a deep copy of this node, that is a fully independant node with all children (if any) also copied. This is mainly useful for instanciating protos.

Implements Node.

wrl::Node::EventInHandle eventIn ( const unsigned int i ) [virtual]

Return a handle on the i th event in of the node or a "unknown" typed handle if there is no such node. emarks This class has no eventIn. This function is useful, with nbEventsIn() if you want to traverse all events in of a Node.

Implements Node.

wrl::Node::EventInHandle eventIn ( const std::string & n ) [virtual]

Return a handle on the event in named n of the node or a "unknown" typed handle if there is no such event. Valid names are:

Implements Node.

wrl::Node::EventOutHandle eventOut ( const unsigned int n ) [virtual]

Return a handle on the i th event out of the node or a "unknown" typed handle if there is no such node. Here is how i is related to fields:

0 : children This function is useful, with nbEventsOut() if you want to traverse all events in of a Node.

Implements Node.

wrl::Node::EventOutHandle eventOut ( const std::string & n ) [virtual]

Return a handle on the event out named n of the node or a "unknown" typed handle if there is no such event. Valid names are:

children

Implements Node.

wrl::Node::FieldHandle field ( const unsigned int n ) [virtual]

Return a handle on the i th field of the node or a "unknown" typed handle if there is no such node. Here is how i is related to fields:

0 : center
1 : child1Url
2 : child2Url
3 : child3Url
4 : child4Url
5 : geoOrigin
6 : geoSystem
7 : range
8 : rootUrl
9 : rootNode This function is useful, with nbFields() if you want to traverse all fields of a Node.

Implements Node.

wrl::Node::FieldHandle field ( const std::string & n ) [virtual]

Return a handle on the field named n of the node or a "unknown" typed handle if there is no such field. Valid names are:

center
child1Url
child2Url
child3Url
child4Url
geoOrigin
geoSystem
range
rootUrl
rootNode

Implements Node.

bool isSetToDefaultValue ( const unsigned int i ) const [virtual]

Implements Node.

unsigned int nbEventsIn ( ) const [inline, virtual]

Returns the number of events in for this node type.

Implements Node.

unsigned int nbEventsOut ( ) const [inline, virtual]

Returns the number of events out for this node type.

Implements Node.

unsigned int nbFields ( ) const [inline, virtual]

Returns the number of fields (exposed or not) for this node type.

Implements Node.

const char * typeName ( ) const [inline, virtual]

Returns "GeoLOD". Useful for printing.

Implements Node.


Public Member Functions
	GeoLOD (const char *name="")
virtual	~GeoLOD ()
virtual unsigned int	nbFields () const
virtual FieldHandle	field (const std::string &n)
virtual FieldHandle	field (const unsigned int i)
virtual bool	isSetToDefaultValue (const unsigned int i) const
virtual unsigned int	nbEventsIn () const
virtual EventInHandle	eventIn (const std::string &n)
virtual EventInHandle	eventIn (const unsigned int i)
virtual unsigned int	nbEventsOut () const
virtual EventOutHandle	eventOut (const std::string &n)
virtual EventOutHandle	eventOut (const unsigned int i)
const char *	typeName () const
virtual Node *	duplicate () const
virtual Node *	duplicate (std::map< const Node , Node > &) const
Public Attributes
Fields
A property or attribute of a node. Each node type has a fixed set of fields. Fields may contain various kinds of data and one or many values. Each field has a default value.
SFString	center
MFString	child1Url
MFString	child2Url
MFString	child3Url
MFString	child4Url
SFNode	geoOrigin
MFString	geoSystem
SFFloat	range
MFString	rootUrl
MFNode	rootNode
Events Out
EventOut< MFNode >	children

GeoLOD Class Reference
[Standard Node Types]

Public Member Functions

Public Attributes

Detailed Description

6.26 GeoLOD

Figure 6.x -- Illustrating the GeoLOD level of detail transition

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation

GeoLOD Class Reference [Standard Node Types]

Public Member Functions

Public Attributes

Detailed Description

6.26 GeoLOD

Figure 6.x -- Illustrating the GeoLOD level of detail transition

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation

GeoLOD Class Reference
[Standard Node Types]