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VolumeAdvection< VelocityGridT, StaggeredVelocity, InterrupterType > Class Template Reference

Performs advections of an arbitrary type of volume in a static velocity field. The advections are performed by means of various derivatives of Semi-Lagrangian integration, i.e. backwards tracking along the hyperbolic characteristics followed by interpolation. More...

`#include <openvdb/tools/VolumeAdvect.h>`

## Public Member Functions

| VolumeAdvection (const VelocityGridT &velGrid, InterrupterType *interrupter=nullptr)
| Constructor.
virtual | ~VolumeAdvection ()
int | spatialOrder () const
| Return the spatial order of accuracy of the advection scheme.
int | temporalOrder () const
| Return the temporal order of accuracy of the advection scheme.
void | setIntegrator (Scheme::SemiLagrangian integrator)
| Set the integrator (see details in the table above).
Scheme::SemiLagrangian | getIntegrator () const
| Return the integrator (see details in the table above).
void | setLimiter (Scheme::Limiter limiter)
| Set the limiter (see details above).
Scheme::Limiter | getLimiter () const
| Retrun the limiter (see details above).
bool | isLimiterOn () const
| Return `true` if a limiter will be applied based on the current settings.
size_t | getGrainSize () const
void | setGrainSize (size_t grainsize)
| Set the grain-size used for multi-threading.
int | getSubSteps () const
void | setSubSteps (int substeps)
| Set the number of sub-steps per integration.
double | getMaxVelocity () const
| Return the maximum magnitude of the velocity in the advection velocity field defined during construction.
template<typename VolumeGridT>
int | getMaxDistance (const VolumeGridT &inGrid, double dt) const
template<typename VolumeGridT, typename VolumeSamplerT>
VolumeGridT::Ptr | advect (const VolumeGridT &inGrid, double timeStep)
template<typename VolumeGridT, typename MaskGridT, typename VolumeSamplerT>
VolumeGridT::Ptr | advect (const VolumeGridT &inGrid, const MaskGridT &mask, double timeStep)

## Detailed Description

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>
class openvdb::v10_0::tools::VolumeAdvection< VelocityGridT, StaggeredVelocity, InterrupterType >

Performs advections of an arbitrary type of volume in a static velocity field. The advections are performed by means of various derivatives of Semi-Lagrangian integration, i.e. backwards tracking along the hyperbolic characteristics followed by interpolation.

Note
  Optionally a limiter can be combined with the higher-order integration schemes MacCormack and BFECC. There are two types of limiters (CLAMP and REVERT) that suppress non-physical oscillations by means of either claminging or reverting to a first-order schemes when the function is not bounded by the cell values used for tri-linear interpolation.

    The supported integrations schemes:
    ///
    ///    ================================================================
    ///    |  Lable | Accuracy |  Integration Scheme   |  Interpolations  |
    ///    |        |Time/Space|                       |  velocity/volume |
    ///    ================================================================
    ///    |  SEMI  |   1/1    | Semi-Lagrangian       |        1/1       |
    ///    |  MID   |   2/1    | Mid-Point             |        2/1       |
    ///    |  RK3   |   3/1    | 3rd Order Runge-Kutta |        3/1       |
    ///    |  RK4   |   4/1    | 4th Order Runge-Kutta |        4/1       |
    ///    |  MAC   |   2/2    | MacCormack            |        2/2       |
    ///    |  BFECC |   2/2    | BFECC                 |        3/2       |
    ///    ================================================================
    ///

## Constructor & Destructor Documentation

## VolumeAdvection()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

VolumeAdvection | ( | const VelocityGridT & | velGrid,
|  | InterrupterType * | interrupter = nullptr )

inline

Constructor.

Parameters

  velGrid | Velocity grid responsible for the (passive) advection.
  interrupter | Optional interrupter used to prematurely end computations.

Note
  The velocity field is assumed to be constant for the duration of the advection.

## ~VolumeAdvection()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

virtual ~VolumeAdvection | ( |  | ) |

inline virtual

## Member Function Documentation

## advect() [1/2]

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>
template<typename VolumeGridT, typename MaskGridT, typename VolumeSamplerT>

VolumeGridT::Ptr advect | ( | const VolumeGridT & | inGrid,
|  | const MaskGridT & | mask,
|  | double | timeStep )

inline

Returns
  Returns a new grid that is the result of passive advection of the active values in inGrid that intersect the active values in `mask`. The time of the output grid is incremented by timeStep.

Parameters

  inGrid | The input grid to be advected (unmodified).
  mask | The mask of active values defining the active voxels in `inGrid` on which to perform advection. Only if a value is active in both grids will it be modified.
  timeStep | Time-step for a single Runge-Kutta integration step.

This method will advect all of the active values in the input inGrid that intersects with the active values in mask. To achieve this a deep-copy is dilated to account for the material transport and finally cropped to the intersection with mask. The dilation step can be slow for large time steps dt or fast moving velocity fields.

Warning
  If the VolumeSamplerT is of higher order the one (i.e. tri-linear interpolation) instabilities are known to occur. To suppress those monotonicity constrains or flux-limiters need to be applies.

Exceptions

  RuntimeError | if inGrid is not aligned with mask or if its voxels are not uniform.

## advect() [2/2]

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>
template<typename VolumeGridT, typename VolumeSamplerT>

VolumeGridT::Ptr advect | ( | const VolumeGridT & | inGrid,
|  | double | timeStep )

inline

Returns
  Returns a new grid that is the result of passive advection of all the active values the input grid by timeStep.

Parameters

  inGrid | The input grid to be advected (unmodified)
  timeStep | Time-step of the Runge-Kutta integrator.

This method will advect all of the active values in the input inGrid. To achieve this a deep-copy is dilated to account for the material transport. This dilation step can be slow for large time steps dt or a velocity field with large magnitudes.

Warning
  If the VolumeSamplerT is of higher order than one (i.e. tri-linear interpolation) instabilities are known to occur. To suppress those monotonicity constrains or flux-limiters need to be applies.

Exceptions

  RuntimeError | if inGrid does not have uniform voxels.

## getGrainSize()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

size_t getGrainSize | ( |  | ) | const

inline

Returns
  the grain-size used for multi-threading

Note
  A grainsize of 0 implies serial execution

## getIntegrator()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

Scheme::SemiLagrangian getIntegrator | ( |  | ) | const

inline

Return the integrator (see details in the table above).

## getLimiter()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

Scheme::Limiter getLimiter | ( |  | ) | const

inline

Retrun the limiter (see details above).

## getMaxDistance()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>
template<typename VolumeGridT>

int getMaxDistance | ( | const VolumeGridT & | inGrid,
|  | double | dt ) const

inline

Returns
  Returns the maximum distance in voxel units of inGrid that a particle can travel in the time-step dt when advected in the velocity field defined during construction.

This method is useful when dilating sparse volume grids to pad boundary regions. Excessive dilation can be computationally expensive so use this method to prevent or warn against run-away computation.

Exceptions

  RuntimeError | if inGrid does not have uniform voxels.

## getMaxVelocity()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

double getMaxVelocity | ( |  | ) | const

inline

Return the maximum magnitude of the velocity in the advection velocity field defined during construction.

## getSubSteps()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

int getSubSteps | ( |  | ) | const

inline

Returns
  the number of sub-steps per integration (always larger than or equal to 1).

## isLimiterOn()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

bool isLimiterOn | ( |  | ) | const

inline

Return `true` if a limiter will be applied based on the current settings.

## setGrainSize()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

void setGrainSize | ( | size_t | grainsize | ) |

inline

Set the grain-size used for multi-threading.

Note
  A grainsize of 0 disables multi-threading

Warning
  A small grainsize can degrade performance, both in terms of time and memory footprint!

## setIntegrator()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

void setIntegrator | ( | Scheme::SemiLagrangian | integrator | ) |

inline

Set the integrator (see details in the table above).

## setLimiter()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

void setLimiter | ( | Scheme::Limiter | limiter | ) |

inline

Set the limiter (see details above).

## setSubSteps()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

void setSubSteps | ( | int | substeps | ) |

inline

Set the number of sub-steps per integration.

Note
  The only reason to increase the sub-step above its default value of one is to reduce the memory footprint due to significant dilation. Values smaller than 1 will be clamped to 1!

## spatialOrder()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

int spatialOrder | ( |  | ) | const

inline

Return the spatial order of accuracy of the advection scheme.

Note
  This is the optimal order in smooth regions. In non-smooth regions the flux-limiter will drop the order of accuracy to add numerical dissipation.

## temporalOrder()

template<typename VelocityGridT = Vec3fGrid, bool StaggeredVelocity = false, typename InterrupterType = util::NullInterrupter>

int temporalOrder | ( |  | ) | const

inline

Return the temporal order of accuracy of the advection scheme.

Note
  This is the optimal order in smooth regions. In non-smooth regions the flux-limiter will drop the order of accuracy to add numerical dissipation.