vtkLocator - abstract base class for objects that accelerate spatial searches

Super Class: vtkObject

Description:

vtkLocator is an abstract base class for spatial search objects, or locators. The principle behind locators is that they divide 3-space into small pieces (or "buckets") that can be quickly found in response to queries like point location, line intersection, or object-object intersection. The purpose of this base class is to provide ivars and methods shared by all locators. The GenerateRepresentation() is one such interesting method. This method works in conjunction with vtkLocatorFilter to create polygonal representations for the locator. For example, if the locator is an OBB tree (i.e., vtkOBBTree.h), then the representation is a set of one or more oriented bounding boxes, depending upon the specified level. Locators typically work as follows. One or more "entities", such as points or cells, are inserted into the tree. These entities are associated with one or more buckets. Then, when preforming geometric operations, the operations are performed first on the buckets, and then if the operation tests positive, then on the entities in the bucket. For example, during collision tests, the locators are collided first to identify intersecting buckets. If an intersection is found, more expensive operations are then carried out on the entities in the bucket. To obtain good performance, locators are often organized in a tree structure. In such a structure, there are frequently multiple "levels" corresponding to different nodes in the tree. So the word level (in the context of the locator) can be used to specify a particular representation in the tree. For example, in an octree (which is a tree with 8 children), level 0 is the bounding box, or root octant, and level 1 consists of its eight children.

See Also:

vtkPointLocator vtkCellLocator vtkOBBTree vtkLocatorFilter

Methods:

• vtkLocator ();
• ~vtkLocator ();
• char *GetClassName ();
• void PrintSelf (ostream &os, vtkIndent indent);
• void SetDataSet (vtkDataSet *);
• vtkDataSetGetDataSet ();
• void SetMaxLevel (int );
• int GetMaxLevel ();
• int GetLevel ();
• void SetAutomatic (int );
• int GetAutomatic ();
• void AutomaticOn ();
• void AutomaticOff ();
• void SetTolerance (float );
• float GetTolerance ();
• void SetRetainCellLists (int );
• int GetRetainCellLists ();
• void RetainCellListsOn ();
• void RetainCellListsOff ();
• virtual void Update ();
• virtual void Initialize ();
• virtual void BuildLocator () = 0;
• virtual void FreeSearchStructure () = 0;
• virtual void GenerateRepresentation (int level, vtkPolyData *pd) = 0;
• long unsigned GetBuildTime ();

Detailed Method Descriptions:

• void SetDataSet (vtkDataSet *);
• vtkDataSetGetDataSet ();

Build the locator from the points/cells defining this dataset.

• void SetMaxLevel (int );
• int GetMaxLevel ();

Set the maximum allowable level for the tree. If the Automatic ivar is off, this will be the target depth of the locator.

• int GetLevel ();

Get the level of the locator (determined automatically if Automatic is true). The value of this ivar may change each time the locator is built.

• void SetAutomatic (int );
• int GetAutomatic ();
• void AutomaticOn ();
• void AutomaticOff ();

Boolean controls whether locator depth/resolution of locator is computed automatically from average number of entities in bucket. If not set, there will be an explicit method to control the construction of the locator (found in the subclass).

• void SetTolerance (float );
• float GetTolerance ();

Specify absolute tolerance (in world coordinates) for performing geometric operations.

• void SetRetainCellLists (int );
• int GetRetainCellLists ();
• void RetainCellListsOn ();
• void RetainCellListsOff ();

Boolean controls whether to maintain list of entities in each bucket. Normally the lists are maintainined, but if the locator is being used as a geometry simplification technique, there is no need to keep them.

• virtual void Update ();

Cause the locator to rebuild itself if it or its input dataset has changed.

• virtual void Initialize ();

Initialize locator. Frees memory and resets object as appropriate.

• virtual void BuildLocator () = 0;

Build the locator from the input dataset.

• virtual void FreeSearchStructure () = 0;

Free the memory required for the spatial data structure.

• virtual void GenerateRepresentation (int level, vtkPolyData *pd) = 0;

Method to build a representation at a particular level. Note that the method GetLevel() returns the maximum number of levels available for the tree. You must provide a vtkPolyData object into which to place the data.

• long unsigned GetBuildTime ();

Return the time of the last data structure build.