#include <vtkModifiedBSPTree.h>
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 lying 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 intented 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.}", }
Definition at line 159 of file vtkModifiedBSPTree.h.
typedef vtkAbstractCellLocator | Superclass |
virtual const char * | GetClassName () |
virtual int | IsA (const char *type) |
void | PrintSelf (ostream &os, vtkIndent indent) |
static int | IsTypeOf (const char *type) |
static vtkModifiedBSPTree * | SafeDownCast (vtkObject *o) |
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 |
Standard Type-Macro
Reimplemented from vtkAbstractCellLocator.
Definition at line 163 of file vtkModifiedBSPTree.h.
vtkModifiedBSPTree::vtkModifiedBSPTree | ( | ) | [protected] |
vtkModifiedBSPTree::~vtkModifiedBSPTree | ( | ) | [protected] |
virtual const char* vtkModifiedBSPTree::GetClassName | ( | ) | [virtual] |
Standard Type-Macro
Reimplemented from vtkAbstractCellLocator.
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 | ( | vtkObject * | o | ) | [static] |
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 192 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 225 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 246 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] |
void vtkModifiedBSPTree::BuildLocatorIfNeeded | ( | ) | [protected] |
void vtkModifiedBSPTree::ForceBuildLocator | ( | ) | [protected] |
void vtkModifiedBSPTree::BuildLocatorInternal | ( | ) | [protected] |
BSPNode* vtkModifiedBSPTree::mRoot [protected] |
Definition at line 269 of file vtkModifiedBSPTree.h.
int vtkModifiedBSPTree::npn [protected] |
Definition at line 270 of file vtkModifiedBSPTree.h.
int vtkModifiedBSPTree::nln [protected] |
Definition at line 271 of file vtkModifiedBSPTree.h.
int vtkModifiedBSPTree::tot_depth [protected] |
Definition at line 272 of file vtkModifiedBSPTree.h.