OpenVDB 11.0.0

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VelocityFields.h
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1// Copyright Contributors to the OpenVDB Project
2// SPDX-License-Identifier: MPL-2.0
3//
4///////////////////////////////////////////////////////////////////////////
5//
6/// @author Ken Museth
7///
8/// @file VelocityFields.h
9///
10/// @brief Defines two simple wrapper classes for advection velocity
11/// fields as well as VelocitySampler and VelocityIntegrator
12///
13///
14/// @details DiscreteField wraps a velocity grid and EnrightField is mostly
15/// intended for debugging (it's an analytical divergence free and
16/// periodic field). They both share the same API required by the
17/// LevelSetAdvection class defined in LevelSetAdvect.h. Thus, any
18/// class with this API should work with LevelSetAdvection.
19///
20/// @warning Note the Field wrapper classes below always assume the velocity
21/// is represented in the world-frame of reference. For DiscreteField
22/// this implies the input grid must contain velocities in world
23/// coordinates.
24
25#ifndef OPENVDB_TOOLS_VELOCITY_FIELDS_HAS_BEEN_INCLUDED
26#define OPENVDB_TOOLS_VELOCITY_FIELDS_HAS_BEEN_INCLUDED
27
28#include <tbb/parallel_reduce.h>
29#include <openvdb/Platform.h>
30#include <openvdb/openvdb.h>
31#include "Interpolation.h" // for Sampler, etc.
32#include <openvdb/math/FiniteDifference.h>
33
34 namespace openvdb {
35 OPENVDB_USE_VERSION_NAMESPACE
36 namespace OPENVDB_VERSION_NAME {
37 namespace tools {
38
39/// @brief Thin wrapper class for a velocity grid
40/// @note Consider replacing BoxSampler with StaggeredBoxSampler
41 template <typename VelGridT, typename Interpolator = BoxSampler>
42 class DiscreteField
43{
44 public:
45 typedef typename VelGridT::ValueType VectorType;
46 typedef typename VectorType::ValueType ValueType;
47 static_assert(std::is_floating_point<ValueType>::value,
48 "DiscreteField requires a floating point grid.");
49
50 DiscreteField(const VelGridT &vel)
51 : mAccessor(vel.tree())
52 , mTransform(&vel.transform())
53 {
54 }
55
56 /// @brief Copy constructor
57 DiscreteField(const DiscreteField& other)
58 : mAccessor(other.mAccessor.tree())
59 , mTransform(other.mTransform)
60 {
61 }
62
63 /// @return const reference to the transform between world and index space
64 /// @note Use this method to determine if a client grid is
65 /// aligned with the coordinate space of the velocity grid.
66 const math::Transform& transform() const { return *mTransform; }
67
68 /// @return the interpolated velocity at the world space position xyz
69 ///
70 /// @warning Not threadsafe since it uses a ValueAccessor! So use
71 /// one instance per thread (which is fine since its lightweight).
72 inline VectorType operator() (const Vec3d& xyz, ValueType/*dummy time*/) const
73 {
74 return Interpolator::sample(mAccessor, mTransform->worldToIndex(xyz));
75 }
76
77 /// @return the velocity at the coordinate space position ijk
78 ///
79 /// @warning Not threadsafe since it uses a ValueAccessor! So use
80 /// one instance per thread (which is fine since its lightweight).
81 inline VectorType operator() (const Coord& ijk, ValueType/*dummy time*/) const
82 {
83 return mAccessor.getValue(ijk);
84 }
85
86 private:
87 const typename VelGridT::ConstAccessor mAccessor;//Not thread-safe
88 const math::Transform* mTransform;
89
90}; // end of DiscreteField
91
92///////////////////////////////////////////////////////////////////////
93
94/// @brief Analytical, divergence-free and periodic velocity field
95/// @note Primarily intended for debugging!
96/// @warning This analytical velocity only produce meaningful values
97/// in the unit box in world space. In other words make sure any level
98/// set surface is fully enclosed in the axis aligned bounding box
99/// spanning 0->1 in world units.
100 template <typename ScalarT = float>
101 class EnrightField
102{
103 public:
104 typedef ScalarT ValueType;
105 typedef math::Vec3<ScalarT> VectorType;
106 static_assert(std::is_floating_point<ScalarT>::value,
107 "EnrightField requires a floating point grid.");
108
109 EnrightField() {}
110
111 /// @return const reference to the identity transform between world and index space
112 /// @note Use this method to determine if a client grid is
113 /// aligned with the coordinate space of this velocity field
114 math::Transform transform() const { return math::Transform(); }
115
116 /// @return the velocity in world units, evaluated at the world
117 /// position xyz and at the specified time
118 inline VectorType operator() (const Vec3d& xyz, ValueType time) const;
119
120 /// @return the velocity at the coordinate space position ijk
121 inline VectorType operator() (const Coord& ijk, ValueType time) const
122 {
123 return (*this)(ijk.asVec3d(), time);
124 }
125}; // end of EnrightField
126
127 template <typename ScalarT>
128 inline math::Vec3<ScalarT>
129 EnrightField<ScalarT>::operator() (const Vec3d& xyz, ValueType time) const
130{
131 const ScalarT pi = math::pi<ScalarT>();
132 const ScalarT phase = pi / ScalarT(3);
133 const ScalarT Px = pi * ScalarT(xyz[0]), Py = pi * ScalarT(xyz[1]), Pz = pi * ScalarT(xyz[2]);
134 const ScalarT tr = math::Cos(ScalarT(time) * phase);
135 const ScalarT a = math::Sin(ScalarT(2)*Py);
136 const ScalarT b = -math::Sin(ScalarT(2)*Px);
137 const ScalarT c = math::Sin(ScalarT(2)*Pz);
138 return math::Vec3<ScalarT>(
139 tr * ( ScalarT(2) * math::Pow2(math::Sin(Px)) * a * c ),
140 tr * ( b * math::Pow2(math::Sin(Py)) * c ),
141 tr * ( b * a * math::Pow2(math::Sin(Pz)) ));
142}
143
144
145///////////////////////////////////////////////////////////////////////
146
147/// Class to hold a Vec3 field interpreted as a velocity field.
148/// Primarily exists to provide a method(s) that integrate a passive
149/// point forward in the velocity field for a single time-step (dt)
150 template<typename GridT = Vec3fGrid,
151 bool Staggered = false,
152 size_t Order = 1>
153 class VelocitySampler
154{
155 public:
156 typedef typename GridT::ConstAccessor AccessorType;
157 typedef typename GridT::ValueType ValueType;
158
159 /// @brief Constructor from a grid
160 VelocitySampler(const GridT& grid):
161 mGrid(&grid),
162 mAcc(grid.getAccessor())
163 {
164 }
165 /// @brief Copy-constructor
166 VelocitySampler(const VelocitySampler& other):
167 mGrid(other.mGrid),
168 mAcc(mGrid->getAccessor())
169 {
170 }
171 /// @brief Samples the velocity at world position onto result. Supports both
172 /// staggered (i.e. MAC) and collocated velocity grids.
173 ///
174 /// @return @c true if any one of the sampled values is active.
175 ///
176 /// @warning Not threadsafe since it uses a ValueAccessor! So use
177 /// one instance per thread (which is fine since its lightweight).
178 template <typename LocationType>
179 inline bool sample(const LocationType& world, ValueType& result) const
180 {
181 const Vec3R xyz = mGrid->worldToIndex(Vec3R(world[0], world[1], world[2]));
182 bool active = Sampler<Order, Staggered>::sample(mAcc, xyz, result);
183 return active;
184 }
185
186 /// @brief Samples the velocity at world position onto result. Supports both
187 /// staggered (i.e. MAC) and co-located velocity grids.
188 ///
189 /// @warning Not threadsafe since it uses a ValueAccessor! So use
190 /// one instance per thread (which is fine since its lightweight).
191 template <typename LocationType>
192 inline ValueType sample(const LocationType& world) const
193 {
194 const Vec3R xyz = mGrid->worldToIndex(Vec3R(world[0], world[1], world[2]));
195 return Sampler<Order, Staggered>::sample(mAcc, xyz);
196 }
197
198 private:
199 // holding the Grids for the transforms
200 const GridT* mGrid; // Velocity vector field
201 AccessorType mAcc;
202};// end of VelocitySampler class
203
204///////////////////////////////////////////////////////////////////////
205
206/// @brief Performs Runge-Kutta time integration of variable order in
207/// a static velocity field.
208///
209/// @note Note that the order of the velocity sampling is controlled
210/// with the SampleOrder template parameter, which defaults
211/// to one, i.e. a tri-linear interpolation kernel.
212 template<typename GridT = Vec3fGrid,
213 bool Staggered = false,
214 size_t SampleOrder = 1>
215 class VelocityIntegrator
216{
217 public:
218 typedef typename GridT::ValueType VecType;
219 typedef typename VecType::ValueType ElementType;
220
221 VelocityIntegrator(const GridT& velGrid):
222 mVelSampler(velGrid)
223 {
224 }
225 /// @brief Variable order Runge-Kutta time integration for a single time step
226 ///
227 /// @param dt Time sub-step for the Runge-Kutte integrator of order OrderRK
228 /// @param world Location in world space coordinates (both input and output)
229 template<size_t OrderRK, typename LocationType>
230 inline void rungeKutta(const ElementType dt, LocationType& world) const
231 {
232 static_assert(OrderRK <= 4);
233 VecType P(static_cast<ElementType>(world[0]),
234 static_cast<ElementType>(world[1]),
235 static_cast<ElementType>(world[2]));
236 // Note the if-branching below is optimized away at compile time
237 if (OrderRK == 0) {
238 return;// do nothing
239 } else if (OrderRK == 1) {
240 VecType V0;
241 mVelSampler.sample(P, V0);
242 P = dt * V0;
243 } else if (OrderRK == 2) {
244 VecType V0, V1;
245 mVelSampler.sample(P, V0);
246 mVelSampler.sample(P + ElementType(0.5) * dt * V0, V1);
247 P = dt * V1;
248 } else if (OrderRK == 3) {
249 VecType V0, V1, V2;
250 mVelSampler.sample(P, V0);
251 mVelSampler.sample(P + ElementType(0.5) * dt * V0, V1);
252 mVelSampler.sample(P + dt * (ElementType(2.0) * V1 - V0), V2);
253 P = dt * (V0 + ElementType(4.0) * V1 + V2) * ElementType(1.0 / 6.0);
254 } else if (OrderRK == 4) {
255 VecType V0, V1, V2, V3;
256 mVelSampler.sample(P, V0);
257 mVelSampler.sample(P + ElementType(0.5) * dt * V0, V1);
258 mVelSampler.sample(P + ElementType(0.5) * dt * V1, V2);
259 mVelSampler.sample(P + dt * V2, V3);
260 P = dt * (V0 + ElementType(2.0) * (V1 + V2) + V3) * ElementType(1.0 / 6.0);
261 }
262 typedef typename LocationType::ValueType OutType;
263 world += LocationType(static_cast<OutType>(P[0]),
264 static_cast<OutType>(P[1]),
265 static_cast<OutType>(P[2]));
266 }
267 private:
268 VelocitySampler<GridT, Staggered, SampleOrder> mVelSampler;
269};// end of VelocityIntegrator class
270
271
272} // namespace tools
273} // namespace OPENVDB_VERSION_NAME
274} // namespace openvdb
275
276#endif // OPENVDB_TOOLS_VELOCITY_FIELDS_HAS_BEEN_INCLUDED
FiniteDifference.h
Interpolation.h
Platform.h
openvdb::v11_0::Grid
Container class that associates a tree with a transform and metadata.
Definition Grid.h:571
openvdb::v11_0::math::Coord
Signed (x, y, z) 32-bit integer coordinates.
Definition Coord.h:25
openvdb::v11_0::math::Coord::asVec3d
Vec3d asVec3d() const
Definition Coord.h:143
openvdb::v11_0::math::Transform
Definition Transform.h:40
openvdb::v11_0::math::Vec3
Definition Vec3.h:24
openvdb::v11_0::tools::DiscreteField
Thin wrapper class for a velocity grid.
Definition VelocityFields.h:43
openvdb::v11_0::tools::DiscreteField::DiscreteField
DiscreteField(const DiscreteField &other)
Copy constructor.
Definition VelocityFields.h:57
openvdb::v11_0::tools::DiscreteField::VectorType
VelGridT::ValueType VectorType
Definition VelocityFields.h:45
openvdb::v11_0::tools::DiscreteField::DiscreteField
DiscreteField(const VelGridT &vel)
Definition VelocityFields.h:50
openvdb::v11_0::tools::DiscreteField::transform
const math::Transform & transform() const
Definition VelocityFields.h:66
openvdb::v11_0::tools::DiscreteField::ValueType
VectorType::ValueType ValueType
Definition VelocityFields.h:46
openvdb::v11_0::tools::EnrightField
Analytical, divergence-free and periodic velocity field.
Definition VelocityFields.h:102
openvdb::v11_0::tools::EnrightField::transform
math::Transform transform() const
Definition VelocityFields.h:114
openvdb::v11_0::tools::EnrightField::VectorType
math::Vec3< ScalarT > VectorType
Definition VelocityFields.h:105
openvdb::v11_0::tools::EnrightField::EnrightField
EnrightField()
Definition VelocityFields.h:109
openvdb::v11_0::tools::EnrightField::ValueType
ScalarT ValueType
Definition VelocityFields.h:104
openvdb::v11_0::tools::VelocityIntegrator
Performs Runge-Kutta time integration of variable order in a static velocity field.
Definition VelocityFields.h:216
openvdb::v11_0::tools::VelocityIntegrator::ElementType
VecType::ValueType ElementType
Definition VelocityFields.h:219
openvdb::v11_0::tools::VelocityIntegrator::VelocityIntegrator
VelocityIntegrator(const GridT &velGrid)
Definition VelocityFields.h:221
openvdb::v11_0::tools::VelocityIntegrator::VecType
GridT::ValueType VecType
Definition VelocityFields.h:218
openvdb::v11_0::tools::VelocityIntegrator::rungeKutta
void rungeKutta(const ElementType dt, LocationType &world) const
Variable order Runge-Kutta time integration for a single time step.
Definition VelocityFields.h:230
openvdb::v11_0::tools::VelocitySampler
Definition VelocityFields.h:154
openvdb::v11_0::tools::VelocitySampler::sample
ValueType sample(const LocationType &world) const
Samples the velocity at world position onto result. Supports both staggered (i.e. MAC) and co-located...
Definition VelocityFields.h:192
openvdb::v11_0::tools::VelocitySampler::sample
bool sample(const LocationType &world, ValueType &result) const
Samples the velocity at world position onto result. Supports both staggered (i.e. MAC) and collocated...
Definition VelocityFields.h:179
openvdb::v11_0::tools::VelocitySampler::ValueType
GridT::ValueType ValueType
Definition VelocityFields.h:157
openvdb::v11_0::tools::VelocitySampler::AccessorType
GridT::ConstAccessor AccessorType
Definition VelocityFields.h:156
openvdb::v11_0::tools::VelocitySampler::VelocitySampler
VelocitySampler(const GridT &grid)
Constructor from a grid.
Definition VelocityFields.h:160
openvdb::v11_0::tools::VelocitySampler::VelocitySampler
VelocitySampler(const VelocitySampler &other)
Copy-constructor.
Definition VelocityFields.h:166
openvdb
Definition Exceptions.h:13
openvdb.h
openvdb::v11_0::tools::Sampler
Provises a unified interface for sampling, i.e. interpolation.
Definition Interpolation.h:64
OPENVDB_VERSION_NAME
#define OPENVDB_VERSION_NAME
The version namespace name for this library version.
Definition version.h.in:121
OPENVDB_USE_VERSION_NAMESPACE
#define OPENVDB_USE_VERSION_NAMESPACE
Definition version.h.in:212