Generate axis aligned BBox tree for raycasting and other Locator based searches. More...

#include <vtkModifiedBSPTree.h>

Inheritance diagram for vtkModifiedBSPTree:

Collaboration diagram for vtkModifiedBSPTree:

Public Member Functions
void	FreeSearchStructure ()
void	BuildLocator ()
virtual void	GenerateRepresentation (int level, vtkPolyData *pd)
virtual void	GenerateRepresentationLeafs (vtkPolyData *pd)
bool	InsideCellBounds (double x[3], vtkIdType cell_ID)
vtkIdListCollection *	GetLeafNodeCellInformation ()

virtual int	IntersectWithLine (double p1[3], double p2[3], double tol, double &t, double x[3], double pcoords[3], int &subId)

virtual int	IntersectWithLine (double p1[3], double p2[3], double tol, double &t, double x[3], double pcoords[3], int &subId, vtkIdType &cellId)

virtual int	IntersectWithLine (double p1[3], double p2[3], double tol, double &t, double x[3], double pcoords[3], int &subId, vtkIdType &cellId, vtkGenericCell *cell)

virtual int	IntersectWithLine (const double p1[3], const double p2[3], vtkPoints points, vtkIdList cellIds)

virtual int	IntersectWithLine (const double p1[3], const double p2[3], const double tol, vtkPoints points, vtkIdList cellIds)

virtual vtkIdType	FindCell (double x[3])

virtual vtkIdType	FindCell (double x[3], double tol2, vtkGenericCell GenCell, double pcoords[3], double weights)
Static Public Member Functions
static vtkModifiedBSPTree *	New ()
Protected Member Functions
	vtkModifiedBSPTree ()
	~vtkModifiedBSPTree ()
void	Subdivide (BSPNode node, Sorted_cell_extents_Lists lists, vtkDataSet *dataSet, vtkIdType nCells, int depth, int maxlevel, vtkIdType maxCells, int &MaxDepth)
virtual int	IntersectCellInternal (vtkIdType cell_ID, const double p1[3], const double p2[3], const double tol, double &t, double ipt[3], double pcoords[3], int &subId)
void	BuildLocatorIfNeeded ()
void	ForceBuildLocator ()
void	BuildLocatorInternal ()
Protected Attributes
BSPNode *	mRoot
int	npn
int	nln
int	tot_depth
typedef vtkAbstractCellLocator	Superclass
static int	IsTypeOf (const char *type)
static vtkModifiedBSPTree *	SafeDownCast (vtkObjectBase *o)
virtual int	IsA (const char *type)
vtkModifiedBSPTree *	NewInstance () const
void	PrintSelf (ostream &os, vtkIndent indent)
virtual vtkObjectBase *	NewInstanceInternal () const

Detailed Description

Generate axis aligned BBox tree for raycasting and other Locator based searches.

vtkModifiedBSPTree creates an evenly balanced BSP tree using a top down implementation. Axis aligned split planes are found which evenly divide cells into two buckets. Generally a split plane will intersect some cells and these are usually stored in both child nodes of the current parent. (Or split into separate cells which we cannot consider in this case). Storing cells in multiple buckets creates problems associated with multiple tests against rays and increases the required storage as complex meshes will have many cells straddling a split plane (and further splits may cause multiple copies of these).

During a discussion with Arno Formella in 1998 he suggested using a third child node to store objects which straddle split planes. I've not seen this published (Yes! - see below), but thought it worth trying. This implementation of the BSP tree creates a third child node for storing cells laying across split planes, the third cell may overlap the other two, but the two 'proper' nodes otherwise conform to usual BSP rules.

The advantage of this implementation is cells only ever lie in one node and mailbox testing is avoided. All BBoxes are axis aligned and a ray cast uses an efficient search strategy based on near/far nodes and rejects all BBoxes using simple tests.

For fast raytracing, 6 copies of cell lists are stored in each leaf node each list is in axis sorted order +/- x,y,z and cells are always tested in the direction of the ray dominant axis. Once an intersection is found any cell or BBox with a closest point further than the I-point can be instantly rejected and raytracing stops as soon as no nodes can be closer than the current best intersection point.

The addition of the 'middle' node upsets the optimal balance of the tree, but is a minor overhead during the raytrace. Each child node is contracted such that it tightly fits all cells inside it, enabling further ray/box rejections.

This class is intended for persons requiring many ray tests and is optimized for this purpose. As no cell ever lies in more than one leaf node, and parent nodes do not maintain cell lists, the memory overhead of the sorted cell lists is 6*num_cells*4 for 6 lists of ints, each num_cells in length. The memory requirement of the nodes themselves is usually of minor significance.

Subdividision is controlled by MaxCellsPerNode - any node with more than this number will be subdivided providing a good split plane can be found and the max depth is not exceeded.

The average cells per leaf will usually be around half the MaxCellsPerNode, though the middle node is usually sparsely populated and lowers the average slightly. The middle node will not be created when not needed. Subdividing down to very small cells per node is not generally suggested as then the 6 stored cell lists are effectively redundant.

Values of MaxcellsPerNode of around 16->128 depending on dataset size will usually give good results.

Cells are only sorted into 6 lists once - before tree creation, each node segments the lists and passes them down to the new child nodes whilst maintaining sorted order. This makes for an efficient subdivision strategy.

NB. The following reference has been sent to me {formella-1995-ray, author = "Arno Formella and Christian Gill", title = "{Ray Tracing: A Quantitative Analysis and a New Practical Algorithm}", journal = "{The Visual Computer}", year = "{1995}", month = dec, pages = "{465--476}", volume = "{11}", number = "{9}", publisher = "{Springer}", keywords = "{ray tracing, space subdivision, plane traversal, octree, clustering, benchmark scenes}", annote = "{We present a new method to accelerate the process of finding nearest ray--object intersections in ray tracing. The algorithm consumes an amount of memory more or less linear in the number of objects. The basic ideas can be characterized with a modified BSP--tree and plane traversal. Plane traversal is a fast linear time algorithm to find the closest intersection point in a list of bounding volumes hit by a ray. We use plane traversal at every node of the high outdegree BSP--tree. Our implementation is competitive to fast ray tracing programs. We present a benchmark suite which allows for an extensive comparison of ray tracing algorithms.}", }

Thanks:: John Biddiscombe for developing and contributing this class

Todo:: ------------- Implement intersection heap for testing rays against transparent objects

@par Style:

This class is currently maintained by J. Biddiscombe who has specially requested that the code style not be modified to the kitware standard. Please respect the contribution of this class by keeping the style as close as possible to the author's original.

Tests:: vtkModifiedBSPTree (Tests)

Definition at line 160 of file vtkModifiedBSPTree.h.

Member Typedef Documentation

typedef vtkAbstractCellLocator vtkModifiedBSPTree::Superclass

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

Definition at line 164 of file vtkModifiedBSPTree.h.

Constructor & Destructor Documentation

vtkModifiedBSPTree::vtkModifiedBSPTree ( ) [protected]

vtkModifiedBSPTree::~vtkModifiedBSPTree ( ) [protected]

Member Function Documentation

static int vtkModifiedBSPTree::IsTypeOf ( const char * type ) [static]

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

virtual int vtkModifiedBSPTree::IsA ( const char * type ) [virtual]

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

static vtkModifiedBSPTree* vtkModifiedBSPTree::SafeDownCast ( vtkObjectBase * o ) [static]

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

virtual vtkObjectBase* vtkModifiedBSPTree::NewInstanceInternal ( ) const [protected, virtual]

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

vtkModifiedBSPTree* vtkModifiedBSPTree::NewInstance ( ) const

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

void vtkModifiedBSPTree::PrintSelf	(	ostream &	os,
		vtkIndent	indent
	)		`[virtual]`

Standard Type-Macro

Reimplemented from vtkAbstractCellLocator.

static vtkModifiedBSPTree* vtkModifiedBSPTree::New ( ) [static]

Construct with maximum 32 cells per node. (average 16->31)

Reimplemented from vtkObject.

void vtkModifiedBSPTree::FreeSearchStructure ( ) [virtual]

Free tree memory

Implements vtkLocator.

void vtkModifiedBSPTree::BuildLocator ( ) [virtual]

Build Tree

Implements vtkLocator.

virtual void vtkModifiedBSPTree::GenerateRepresentation	(	int	level,
		vtkPolyData *	pd
	)		`[virtual]`

Generate BBox representation of Nth level

Implements vtkLocator.

virtual void vtkModifiedBSPTree::GenerateRepresentationLeafs ( vtkPolyData * pd ) [virtual]

Generate BBox representation of all leaf nodes

virtual int vtkModifiedBSPTree::IntersectWithLine	(	double	p1[3],
		double	p2[3],
		double	tol,
		double &	t,
		double	x[3],
		double	pcoords[3],
		int &	subId
	)		`[inline, virtual]`

Return intersection point (if any) of finite line with cells contained in cell locator.

Reimplemented from vtkAbstractCellLocator.

Definition at line 193 of file vtkModifiedBSPTree.h.

virtual int vtkModifiedBSPTree::IntersectWithLine	(	double	p1[3],
		double	p2[3],
		double	tol,
		double &	t,
		double	x[3],
		double	pcoords[3],
		int &	subId,
		vtkIdType &	cellId
	)		`[virtual]`

Return intersection point (if any) AND the cell which was intersected by the finite line. Uses fast tree-search BBox rejection tests.

Reimplemented from vtkAbstractCellLocator.

virtual int vtkModifiedBSPTree::IntersectWithLine	(	double	p1[3],
		double	p2[3],
		double	tol,
		double &	t,
		double	x[3],
		double	pcoords[3],
		int &	subId,
		vtkIdType &	cellId,
		vtkGenericCell *	cell
	)		`[virtual]`

Return intersection point (if any) AND the cell which was intersected by the finite line. The cell is returned as a cell id and as a generic cell.

Reimplemented from vtkAbstractCellLocator.

virtual int vtkModifiedBSPTree::IntersectWithLine	(	const double	p1[3],
		const double	p2[3],
		vtkPoints *	points,
		vtkIdList *	cellIds
	)		`[inline, virtual]`

Take the passed line segment and intersect it with the data set. This method assumes that the data set is a vtkPolyData that describes a closed surface, and the intersection points that are returned in 'points' alternate between entrance points and exit points. The return value of the function is 0 if no intersections were found, -1 if point 'a0' lies inside the closed surface, or +1 if point 'a0' lies outside the closed surface. Either 'points' or 'cellIds' can be set to NULL if you don't want to receive that information. This method is currently only implemented in vtkOBBTree

Reimplemented from vtkAbstractCellLocator.

Definition at line 226 of file vtkModifiedBSPTree.h.

virtual int vtkModifiedBSPTree::IntersectWithLine	(	const double	p1[3],
		const double	p2[3],
		const double	tol,
		vtkPoints *	points,
		vtkIdList *	cellIds
	)		`[virtual]`

Take the passed line segment and intersect it with the data set. The return value of the function is 0 if no intersections were found. For each intersection found, the vtkPoints and CellIds objects have the relevant information added in order of intersection increasing from ray start to end. If either vtkPoints or CellIds are NULL pointers, then no information is generated for that list.

virtual vtkIdType vtkModifiedBSPTree::FindCell ( double x[3] ) [inline, virtual]

Returns the Id of the cell containing the point, returns -1 if no cell found. This interface uses a tolerance of zero

Reimplemented from vtkAbstractCellLocator.

Definition at line 247 of file vtkModifiedBSPTree.h.

virtual vtkIdType vtkModifiedBSPTree::FindCell	(	double	x[3],
		double	tol2,
		vtkGenericCell *	GenCell,
		double	pcoords[3],
		double *	weights
	)		`[virtual]`

Test a point to find if it is inside a cell. Returns the cellId if inside or -1 if not.

Reimplemented from vtkAbstractCellLocator.

bool vtkModifiedBSPTree::InsideCellBounds	(	double	x[3],
		vtkIdType	cell_ID
	)		`[virtual]`

Quickly test if a point is inside the bounds of a particular cell. Some locators cache cell bounds and this function can make use of fast access to the data.

Reimplemented from vtkAbstractCellLocator.

vtkIdListCollection* vtkModifiedBSPTree::GetLeafNodeCellInformation ( )

After subdivision has completed, one may wish to query the tree to find which cells are in which leaf nodes. This function returns a list which holds a cell Id list for each leaf node.

void vtkModifiedBSPTree::Subdivide	(	BSPNode *	node,
		Sorted_cell_extents_Lists *	lists,
		vtkDataSet *	dataSet,
		vtkIdType	nCells,
		int	depth,
		int	maxlevel,
		vtkIdType	maxCells,
		int &	MaxDepth
	)		`[protected]`

virtual int vtkModifiedBSPTree::IntersectCellInternal	(	vtkIdType	cell_ID,
		const double	p1[3],
		const double	p2[3],
		const double	tol,
		double &	t,
		double	ipt[3],
		double	pcoords[3],
		int &	subId
	)		`[protected, virtual]`