vtkLocator

Section: Visualization Toolkit Filtering Classes

Usage

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 performing 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.

To create an instance of class vtkLocator, simply invoke its constructor as follows

  obj = vtkLocator

Methods

The class vtkLocator has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkLocator class.