This structure allows to encode contact patches. A contact patch is defined by a set of points belonging to a subset of a plane passing by p and supported by n, where n = Contact::normal and p = Contact::pos. If we denote by P this plane and by S1 and S2 the first and second shape of a collision pair, a contact patch is represented as a polytope which vertices all belong to P & S1 & S2, where & denotes the set-intersection. Since a contact patch is a subset of a plane supported by n, it has a preferred direction. In Coal, the Contact::normal points from S1 to S2. In the same way, a contact patch points by default from S1 to S2.
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#include <coal/collision_data.h>
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| enum | PatchDirection { DEFAULT = 0
, INVERTED = 1
} |
| | Direction of ContactPatch. When doing collision detection, the convention of Coal is that the normal always points from the first to the second shape of the collision pair i.e. from shape1 to shape2 when calling collide(shape1, shape2). The PatchDirection enum allows to identify if the patch points from shape 1 to shape 2 (Default type) or from shape 2 to shape 1 (Inverted type). The Inverted type should only be used for internal Coal computations (it allows to properly define two separate contact patches in the same frame). More...
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| using | Polygon = std::vector< Vec2s > |
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| | ContactPatch (size_t preallocated_size=default_preallocated_size) |
| | Default constructor. Note: the preallocated size does not determine the maximum number of points in the patch, it only serves as preallocation if the maximum size of the patch is known in advance. Coal will automatically expand/shrink the contact patch if needed. More...
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| Vec3s | getNormal () const |
| | Normal of the contact patch, expressed in the WORLD frame. More...
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| size_t | size () const |
| | Returns the number of points in the contact patch. More...
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| void | addPoint (const Vec3s &point_3d) |
| | Add a 3D point to the set, expressed in the world frame. More...
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| Vec3s | getPoint (const size_t i) const |
| | Get the i-th point of the set, expressed in the 3D world frame. More...
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| Vec3s | getPointShape1 (const size_t i) const |
| | Get the i-th point of the contact patch, projected back onto the first shape of the collision pair. This point is expressed in the 3D world frame. More...
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| Vec3s | getPointShape2 (const size_t i) const |
| | Get the i-th point of the contact patch, projected back onto the first shape of the collision pair. This 3D point is expressed in the world frame. More...
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| Polygon & | points () |
| | Getter for the 2D points in the set. More...
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| const Polygon & | points () const |
| | Const getter for the 2D points in the set. More...
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| Vec2s & | point (const size_t i) |
| | Getter for the i-th 2D point in the set. More...
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| const Vec2s & | point (const size_t i) const |
| | Const getter for the i-th 2D point in the set. More...
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| void | clear () |
| | Clear the set. More...
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| bool | operator== (const ContactPatch &other) const |
| | Whether two contact patches are the same or not. More...
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| bool | isSame (const ContactPatch &other, const Scalar tol=Eigen::NumTraits< Scalar >::dummy_precision()) const |
| | Whether two contact patches are the same or not. Checks for different order of the points. More...
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| static constexpr size_t | default_preallocated_size = 12 |
| | Default maximum size of the polygon representing the contact patch. Used to pre-allocate memory for the patch. More...
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This structure allows to encode contact patches. A contact patch is defined by a set of points belonging to a subset of a plane passing by p and supported by n, where n = Contact::normal and p = Contact::pos. If we denote by P this plane and by S1 and S2 the first and second shape of a collision pair, a contact patch is represented as a polytope which vertices all belong to P & S1 & S2, where & denotes the set-intersection. Since a contact patch is a subset of a plane supported by n, it has a preferred direction. In Coal, the Contact::normal points from S1 to S2. In the same way, a contact patch points by default from S1 to S2.
- Note
- For now (April 2024), a
ContactPatch is a polygon (2D polytope), so the points of the set, forming the convex-hull of the polytope, are stored in a counter-clockwise fashion.
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If needed, the internal algorithms of Coal can easily be extended to compute a contact volume instead of a contact patch.
◆ Polygon
◆ PatchDirection
Direction of ContactPatch. When doing collision detection, the convention of Coal is that the normal always points from the first to the second shape of the collision pair i.e. from shape1 to shape2 when calling collide(shape1, shape2). The PatchDirection enum allows to identify if the patch points from shape 1 to shape 2 (Default type) or from shape 2 to shape 1 (Inverted type). The Inverted type should only be used for internal Coal computations (it allows to properly define two separate contact patches in the same frame).
| Enumerator |
|---|
| DEFAULT | |
| INVERTED | |
◆ ContactPatch()
Default constructor. Note: the preallocated size does not determine the maximum number of points in the patch, it only serves as preallocation if the maximum size of the patch is known in advance. Coal will automatically expand/shrink the contact patch if needed.
◆ addPoint()
| void coal::ContactPatch::addPoint |
( |
const Vec3s & |
point_3d | ) |
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inline |
Add a 3D point to the set, expressed in the world frame.
- Note
- This function takes a 3D point and expresses it in the local frame of the set. It then takes only the x and y components of the vector, effectively doing a projection onto the plane to which the set belongs. TODO(louis): if necessary, we can store the offset to the plane (x, y).
◆ clear()
| void coal::ContactPatch::clear |
( |
| ) |
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inline |
◆ getNormal()
| Vec3s coal::ContactPatch::getNormal |
( |
| ) |
const |
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inline |
Normal of the contact patch, expressed in the WORLD frame.
◆ getPoint()
| Vec3s coal::ContactPatch::getPoint |
( |
const size_t |
i | ) |
const |
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inline |
Get the i-th point of the set, expressed in the 3D world frame.
◆ getPointShape1()
| Vec3s coal::ContactPatch::getPointShape1 |
( |
const size_t |
i | ) |
const |
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inline |
Get the i-th point of the contact patch, projected back onto the first shape of the collision pair. This point is expressed in the 3D world frame.
◆ getPointShape2()
| Vec3s coal::ContactPatch::getPointShape2 |
( |
const size_t |
i | ) |
const |
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inline |
Get the i-th point of the contact patch, projected back onto the first shape of the collision pair. This 3D point is expressed in the world frame.
◆ isSame()
| bool coal::ContactPatch::isSame |
( |
const ContactPatch & |
other, |
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const Scalar |
tol = Eigen::NumTraits<Scalar>::dummy_precision() |
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) |
| const |
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inline |
Whether two contact patches are the same or not. Checks for different order of the points.
◆ operator==()
| bool coal::ContactPatch::operator== |
( |
const ContactPatch & |
other | ) |
const |
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inline |
Whether two contact patches are the same or not.
- Note
- This compares the two sets terms by terms. However, two contact patches can be identical, but have a different order for their points. Use
isEqual in this case.
◆ point() [1/2]
| Vec2s& coal::ContactPatch::point |
( |
const size_t |
i | ) |
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inline |
Getter for the i-th 2D point in the set.
◆ point() [2/2]
| const Vec2s& coal::ContactPatch::point |
( |
const size_t |
i | ) |
const |
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inline |
Const getter for the i-th 2D point in the set.
◆ points() [1/2]
| Polygon& coal::ContactPatch::points |
( |
| ) |
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inline |
Getter for the 2D points in the set.
◆ points() [2/2]
| const Polygon& coal::ContactPatch::points |
( |
| ) |
const |
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inline |
Const getter for the 2D points in the set.
◆ size()
| size_t coal::ContactPatch::size |
( |
| ) |
const |
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inline |
Returns the number of points in the contact patch.
◆ default_preallocated_size
| constexpr size_t coal::ContactPatch::default_preallocated_size = 12 |
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staticconstexpr |
Default maximum size of the polygon representing the contact patch. Used to pre-allocate memory for the patch.
◆ direction
Direction of this contact patch.
◆ m_points
| Polygon coal::ContactPatch::m_points |
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protected |
Container for the vertices of the set.
◆ penetration_depth
| Scalar coal::ContactPatch::penetration_depth |
Penetration depth of the contact patch. This value corresponds to the signed distance d between the shapes.
- Note
- For each contact point
p in the patch of normal n, p1 = p - 0.5*d*n and p2 = p + 0.5*d*n define a pair of witness points. p1 belongs to the surface of the first shape and p2 belongs to the surface of the second shape. For any pair of witness points, we always have p2 - p1 = d * n. The vector d * n is called a minimum separation vector: if S1 is translated by it, S1 and S2 are not in collision anymore.
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Although there may exist multiple minimum separation vectors between two shapes, the term "minimum" comes from the fact that it's impossible to find a different separation vector which has a smaller norm than
d * n.
◆ tf
Frame of the set, expressed in the world coordinates. The z-axis of the frame's rotation is the contact patch normal.
The documentation for this struct was generated from the following file:
