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when libccd reports the nearest feature is an edge, validate the resu…
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…lt. Also fixes flexible-collision-library#319.
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@hongkai-dai
hongkai-dai committed Apr 6, 2019
1 parent 5e93762 commit 35eae12
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Showing 2 changed files with 237 additions and 11 deletions.
138 changes: 127 additions & 11 deletions include/fcl/narrowphase/detail/convexity_based_algorithm/gjk_libccd-inl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -369,6 +369,11 @@ static int doSimplex2(ccd_simplex_t *simplex, ccd_vec3_t *dir) {
return 0;
}

static bool isAbsValueLessThanEpsSquared(ccd_real_t val) {
return std::abs(val) < std::numeric_limits<ccd_real_t>::epsilon() *
std::numeric_limits<ccd_real_t>::epsilon();
}

// TODO(SeanCurtis-TRI): Define the return value:
// 1: (like doSimplex2) --> origin is "in" the simplex.
// 0:
Expand All @@ -386,10 +391,8 @@ static int doSimplex3(ccd_simplex_t *simplex, ccd_vec3_t *dir)
C = ccdSimplexPoint(simplex, 0);

// check touching contact
// TODO(SeanCurtis-TRI): This is dist2 (i.e., dist_squared) and should be
// tested to be zero within a tolerance of ε² (and not just ε).
dist = ccdVec3PointTriDist2(ccd_vec3_origin, &A->v, &B->v, &C->v, nullptr);
if (ccdIsZero(dist)){
if (isAbsValueLessThanEpsSquared(dist)){
return 1;
}

Expand Down Expand Up @@ -460,11 +463,6 @@ static int doSimplex3(ccd_simplex_t *simplex, ccd_vec3_t *dir)
return 0;
}

static bool isAbsValueLessThanEpsSquared(ccd_real_t val) {
return std::abs(val) < std::numeric_limits<ccd_real_t>::epsilon() *
std::numeric_limits<ccd_real_t>::epsilon();
}

static int doSimplex4(ccd_simplex_t *simplex, ccd_vec3_t *dir)
{
const ccd_support_t *A, *B, *C, *D;
Expand Down Expand Up @@ -940,6 +938,28 @@ static bool triangle_area_is_zero(const ccd_vec3_t& a, const ccd_vec3_t& b,
return false;
}

/**
* Determines if the point P is on the line segment AB.
* If A, B, P are coincident, report true.
*/
static bool is_point_on_line_segment(const ccd_vec3_t& p, const ccd_vec3_t& a, const ccd_vec3_t& b) {
if (are_coincident(a, b)) {
return are_coincident(a, p);
}
// A and B are not coincident, if the triangle ABP has non-zero area, then P
// is not on the line adjoining AB, and hence not on the line segment AB.
if (!triangle_area_is_zero(a, b, p)) {
return false;
}
// P is on the line adjoinging AB. If P is on the line segment AB, then
// PA.dot(PB) <= 0.
ccd_vec3_t PA, PB;
ccdVec3Sub2(&PA, &p, &a);
ccdVec3Sub2(&PB, &p, &b);
return ccdVec3Dot(&PA, &PB) <= 0;
}


/**
* Computes the normal vector of a triangular face on a polytope, and the normal
* vector points outward from the polytope. Notice we assume that the origin
Expand Down Expand Up @@ -1286,7 +1306,6 @@ static int expandPolytope(ccd_pt_t *polytope, ccd_pt_el_t *el,
"The visible feature is a vertex. This should already have been "
"identified as a touching contact");
}

// Start with the face on which the closest point lives
if (el->type == CCD_PT_FACE) {
start_face = reinterpret_cast<ccd_pt_face_t*>(el);
Expand Down Expand Up @@ -1533,6 +1552,95 @@ static int __ccdGJK(const void *obj1, const void *obj2,
return -1;
}

/**
* When the nearest feature of a polytope to the origin is an edge, and the
* origin is inside the polytope, it implies one of the following conditions
* 1. The origin lies exactly on that edge
* 2. The two neighbouring faces of that edge are coplanar, and the projection
* of the origin onto that plane is on the edge. Inside this function, we will
* verify if one of these two conditions are true. If not, we will modify the
* nearest feature stored inside @p polytope, such that it stores the right
* nearest feature and distance.
* @param polytope The polytope whose nearest feature is being verified (and
* corrected if the edge should not be nearest feature).
* @note Only call this function in the EPA functions, where the origin should
* be inside the polytope.
*/
static void validateNearestFeatureOfPolytopeBeingEdge(ccd_pt_t* polytope) {
if (polytope->nearest_type == CCD_PT_EDGE) {
// Only verify the feature if the nearest feature is an edge.

ccd_pt_edge_t* nearest_edge =
reinterpret_cast<ccd_pt_edge_t*>(polytope->nearest);
// Find the outward normals on the two neighbouring faces of the edge, if
// the origin is on the "inner" side of these two faces, then we regard the
// origin to be inside the polytope. Note that these @p face_normals are
// normalized.
std::array<ccd_vec3_t, 2> face_normals;
std::array<double, 2> origin_to_face_distance;
for (int i = 0; i < 2; ++i) {
face_normals[i] =
faceNormalPointingOutward(polytope, nearest_edge->faces[i]);
ccdVec3Normalize(&(face_normals[i]));
// If the origin is on the "inner" side of the face, then
// face_normals[i].dot(origin - edge.vertex) <= 0.
origin_to_face_distance[i] =
-ccdVec3Dot(&(face_normals[i]), &(nearest_edge->vertex[0]->v.v));
if (origin_to_face_distance[i] > 0) {
FCL_THROW_FAILED_AT_THIS_CONFIGURATION(
"The origin is outside of the polytope. This should already have "
"been identified as separating.");
}
}
// If the two neighbouring faces are co-planar, then their face normals are
// the same.
bool are_neighbouring_faces_coplanar = true;
for (int i = 0; i < 3; ++i) {
if (!ccdIsZero(face_normals[0].v[i] - face_normals[1].v[i])) {
are_neighbouring_faces_coplanar = false;
break;
}
}
bool is_edge_closest_feature = true;
if (!are_neighbouring_faces_coplanar) {
// If the closest feature is an edge, and the two neighouring faces are
// not co-planar, then the origin has to be on that edge, and hence the
// distance from the origin to the face has to be 0.
if (!ccdIsZero(origin_to_face_distance[0]) ||
!ccdIsZero(origin_to_face_distance[1])) {
// The distance from the origin to the face is not 0. This violates the
// assumption that the closest feature is an edge. We will recompute the
// closest feature.
is_edge_closest_feature = false;
}
} else {
// The neighbouring faces are coplanar.
// We compute the projection of the origin onto the plane as
// -face_normals[0] * origin_to_face_distance[0]
ccd_vec3_t origin_projection_on_edge = face_normals[0];
ccdVec3Scale(&origin_projection_on_edge, -origin_to_face_distance[0]);
if (!is_point_on_line_segment(origin_projection_on_edge,
nearest_edge->vertex[0]->v.v,
nearest_edge->vertex[1]->v.v)) {
is_edge_closest_feature = false;
}
}
if (!is_edge_closest_feature) {
// We assume that libccd is not crazily wrong. Although the closest
// feature should not be the edge, it is near that edge. Hence we pick one
// of the neighbouring faces as the closest feature.
polytope->nearest_type = CCD_PT_FACE;
// Note origin_to_face_distance is the signed distance.
const int closest_face =
origin_to_face_distance[0] < origin_to_face_distance[1] ? 1 : 0;
polytope->nearest =
reinterpret_cast<ccd_pt_el_t*>(nearest_edge->faces[closest_face]);
// polytope->nearest_dist stores the SQUARED distance.
polytope->nearest_dist = origin_to_face_distance[closest_face] *
origin_to_face_distance[closest_face];
}
}
}

static int __ccdEPA(const void *obj1, const void *obj2,
const ccd_t *ccd,
Expand All @@ -1557,6 +1665,7 @@ static int __ccdEPA(const void *obj1, const void *obj2,
ret = simplexToPolytope2(obj1, obj2, ccd, simplex, polytope, nearest);
}


if (ret == -1){
// touching contact
return 0;
Expand All @@ -1566,12 +1675,19 @@ static int __ccdEPA(const void *obj1, const void *obj2,
}

while (1){
// get triangle nearest to origin
// get triangle nearest to origin
*nearest = ccdPtNearest(polytope);
if (polytope->nearest_type == CCD_PT_EDGE) {
// When libccd thinks the nearest feature is an edge, that is often
// wrong, hence we validate the nearest feature by ourselves.
validateNearestFeatureOfPolytopeBeingEdge(polytope);
*nearest = ccdPtNearest(polytope);
}

// get next support point
if (nextSupport(polytope, obj1, obj2, ccd, *nearest, &supp) != 0)
if (nextSupport(polytope, obj1, obj2, ccd, *nearest, &supp) != 0) {
break;
}

// expand nearest triangle using new point - supp
if (expandPolytope(polytope, *nearest, &supp) != 0)
Expand Down
110 changes: 110 additions & 0 deletions test/test_fcl_signed_distance.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,106 @@ void test_distance_spherecapsule(GJKSolverType solver_type)
}
}

template <typename S>
void test_distance_cylinder_sphere1() {
// This is a specific case that has cropped up in the wild that reaches the
// unexpected `expandPolytope()` error, where the nearest point and the new
// vertiex botih lie on an edge. It turns out that libccd incorrectly thinks
// that the edge is the nearest feature, while actually one of the
// neighbouring face is. This test confirms that the bug is fixed, by the
// function validateNearestFeatureOfPolytopeBeingEdge.
using CollisionGeometryPtr_t = std::shared_ptr<fcl::CollisionGeometry<S>>;
const S cylinder_radius = 0.03;
const S cylinder_length = 0.65;
CollisionGeometryPtr_t cylinder_geo(
new fcl::Cylinder<S>(cylinder_radius, cylinder_length));
Transform3<S> X_WC = Transform3<S>::Identity();
X_WC.translation() <<0.6, 0,0.325;
fcl::CollisionObject<S> cylinder(cylinder_geo, X_WC);

const S sphere_radius = 0.055;
CollisionGeometryPtr_t sphere_geo(new fcl::Sphere<S>(sphere_radius));
Transform3<S> X_WS = Transform3<S>::Identity();
// clang-format off
X_WS.matrix() << -0.9954758066974283004, -0.029586630161622884394, 0.090291470227168560414, 0.54197940181714598928,
-0.085103478665251586222, -0.14494505659711237611, -0.98577295990868651909, -0.062117502536077888464,
0.042253002250460247602, -0.98899725069574340175, 0.14177137199407846557, 0.60162365763662117857,
0, 0, 0, 1;
// clang-format on
fcl::CollisionObject<S> sphere(sphere_geo, X_WS);

fcl::DistanceRequest<S> request;
request.gjk_solver_type = GJKSolverType::GST_LIBCCD;
request.distance_tolerance = 9.9999999999999995475e-07;
request.enable_signed_distance = true;
fcl::DistanceResult<S> result;

EXPECT_NO_THROW(fcl::distance(&cylinder, &sphere, request, result));
// The two objects are penetrating.
EXPECT_NEAR(-(result.nearest_points[0] - result.nearest_points[1]).norm(),
result.min_distance, request.distance_tolerance);
// p_CPc is the position of the witness point Pc on the cylinder, measured
// and expressed in the cylinder frame C.
const Vector3<S> p_CPc = X_WC.inverse() * result.nearest_points[0];
EXPECT_LE(std::abs(p_CPc(2)), cylinder_length / 2);
EXPECT_LE(p_CPc.template head<2>().norm(), cylinder_radius);
// p_SPs is the position of the witness point Ps on the sphere, measured and
// expressed in the sphere frame S.
const Vector3<S> p_SPs = X_WS.inverse() * result.nearest_points[1];
EXPECT_LE(p_SPs.norm(), sphere_radius);
}

// This is a *specific* case that has cropped up in the wild that reaches the
// unexpected `expandPolytope()` error. This error was reported in
// https://github.com/flexible-collision-library/fcl/issues/319
template <typename S>
void test_distance_cylinder_box1() {
using CollisionGeometryPtr_t = std::shared_ptr<fcl::CollisionGeometryd>;
const S cylinder_radius = 0.05;
const S cylinder_length = 0.06;
CollisionGeometryPtr_t cylinder_geo(
new fcl::Cylinder<S>(cylinder_radius, cylinder_length));
Transform3<S> X_WC = Transform3<S>::Identity();
X_WC.matrix() << -0.99999999997999022838, 6.2572835802045040178e-10,
6.3260669852976095481e-06, 0.57500009756757608503,
6.3260669851683709551e-06, -6.3943303429958554955e-10,
0.99999999997999056145, -0.42711963046787942977,
6.2573180158128459924e-10, 1, 6.3942912945996747041e-10,
1.1867093358746836351, 0, 0, 0, 1;
fcl::CollisionObject<S> cylinder(cylinder_geo, X_WC);

const Vector3<S> box_size(0.025, 0.35, 1.845);
CollisionGeometryPtr_t box_geo(
new fcl::Box<S>(box_size(0), box_size(1), box_size(2)));
Transform3<S> X_WB = Transform3<S>::Identity();
X_WB.matrix() << 6.1232339957367660359e-17, -1, 0, 0.80000000000000004441, 1,
6.1232339957367660359e-17, 0, -0.45750000000000001776, 0, 0, 1,
1.0224999999999999645, 0, 0, 0, 1;
fcl::CollisionObject<S> box(box_geo, X_WB);

fcl::DistanceRequest<S> request;
request.gjk_solver_type = GJKSolverType::GST_LIBCCD;
request.distance_tolerance = 9.9999999999999995475e-07;
request.enable_signed_distance = true;
fcl::DistanceResult<S> result;

EXPECT_NO_THROW(fcl::distance(&cylinder, &box, request, result));
EXPECT_NEAR(result.min_distance,
(result.nearest_points[0] - result.nearest_points[1]).norm(),
request.distance_tolerance);
// p_CPc is the position of the witness point Pc on the cylinder, measured
// and expressed in the cylinder frame C.
const Vector3<S> p_CPc = X_WC.inverse() * result.nearest_points[0];
EXPECT_LE(std::abs(p_CPc(2)), cylinder_length / 2);
EXPECT_LE(p_CPc.template head<2>().norm(), cylinder_radius);
// p_BPb is the position of the witness point Pb on the box, measured and
// expressed in the box frame B.
const Vector3<S> p_BPb = X_WB.inverse() * result.nearest_points[1];
EXPECT_TRUE((p_BPb.array().abs() <=
box_size.array() / 2 + 10 * std::numeric_limits<S>::epsilon())
.all());
}

//==============================================================================

GTEST_TEST(FCL_NEGATIVE_DISTANCE, sphere_sphere_ccd)
Expand All @@ -186,6 +286,16 @@ GTEST_TEST(FCL_NEGATIVE_DISTANCE, sphere_capsule_indep)
test_distance_spherecapsule<double>(GST_INDEP);
}

GTEST_TEST(FCL_SIGNED_DISTANCE, cylinder_sphere1_ccd)
{
test_distance_cylinder_sphere1<double>();
}

GTEST_TEST(FCL_SIGNED_DISTANCE, cylinder_box1_ccd)
{
test_distance_cylinder_box1<double>();
}

//==============================================================================
int main(int argc, char* argv[])
{
Expand Down

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