LSST Applications  21.0.0+04719a4bac,21.0.0-1-ga51b5d4+f5e6047307,21.0.0-11-g2b59f77+a9c1acf22d,21.0.0-11-ga42c5b2b+86977b0b17,21.0.0-12-gf4ce030+754bb092b1,21.0.0-13-g1721dae+dfd6acfe73,21.0.0-13-g3a573fe+0dbdb475db,21.0.0-15-g5a7caf0+8de75914b0,21.0.0-16-g0fb55c1+b60e2d390c,21.0.0-19-g4cded4ca+71a93a33c0,21.0.0-2-g103fe59+bb20972958,21.0.0-2-g45278ab+04719a4bac,21.0.0-2-g5242d73+3ad5d60fb1,21.0.0-2-g7f82c8f+8babb168e8,21.0.0-2-g8f08a60+06509c8b61,21.0.0-2-g8faa9b5+616205b9df,21.0.0-2-ga326454+8babb168e8,21.0.0-2-gde069b7+5e4aea9c2f,21.0.0-2-gecfae73+1d3a86e577,21.0.0-2-gfc62afb+3ad5d60fb1,21.0.0-25-g1d57be3cd+e73869a214,21.0.0-3-g357aad2+ed88757d29,21.0.0-3-g4a4ce7f+3ad5d60fb1,21.0.0-3-g4be5c26+3ad5d60fb1,21.0.0-3-g65f322c+e0b24896a3,21.0.0-3-g7d9da8d+616205b9df,21.0.0-3-ge02ed75+a9c1acf22d,21.0.0-4-g591bb35+a9c1acf22d,21.0.0-4-g65b4814+b60e2d390c,21.0.0-4-gccdca77+0de219a2bc,21.0.0-4-ge8a399c+6c55c39e83,21.0.0-5-gd00fb1e+6aa56f371b,21.0.0-6-gc675373+3ad5d60fb1,21.0.0-7-g04766d7+cd19d05db2,21.0.0-7-gdf92d54+04719a4bac,21.0.0-8-g5674e7b+d1bd76f71f,master-gac4afde19b+a9c1acf22d,v22.0.0.rc2,v22.0.x-gc9c83ed91b+4fb2b8f86e
LSST Data Management Base Package
utils.cc
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22 
25 
26 #include "lsst/sphgeom/utils.h"
27 
28 #include <cmath>
29 
31 
32 
33 namespace lsst {
34 namespace sphgeom {
35 
37  Vector3d const & a,
38  Vector3d const & b,
39  Vector3d const & n)
40 {
41  Vector3d vxn = v.cross(n);
42  if (vxn.dot(a) > 0.0 && vxn.dot(b) < 0.0) {
43  // v is in the lune defined by the half great circle passing through
44  // n and a and the half great circle passing through n and b, so p
45  // is in the interior of the great circle segment from a to b. The
46  // angle θ between p and v satisfies ‖v‖ ‖n‖ sin θ = |v·n|,
47  // and ‖v‖ ‖n‖ cos θ = ‖v × n‖. The desired squared chord length is
48  // 4 sin²(θ/2).
49  double s = std::fabs(v.dot(n));
50  double c = vxn.getNorm();
51  double theta = (c == 0.0) ? 0.5 * PI : std::atan(s / c);
52  double d = std::sin(0.5 * theta);
53  return 4.0 * d * d;
54  }
55  return 4.0;
56 }
57 
59  Vector3d const & a,
60  Vector3d const & b,
61  Vector3d const & n)
62 {
63  Vector3d vxn = v.cross(n);
64  if (vxn.dot(a) < 0.0 && vxn.dot(b) > 0.0) {
65  // v is in the lune defined by the half great circle passing through
66  // n and -a and the half great circle passing through n and -b, so p
67  // is in the interior of the great circle segment from a to b. The
68  // angle θ between p and v satisfies ‖v‖ ‖n‖ sin θ = |v·n|,
69  // and ‖v‖ ‖n‖ cos θ = -‖v × n‖. The desired squared chord length is
70  // 4 sin²(θ/2).
71  double s = std::fabs(v.dot(n));
72  double c = - vxn.getNorm();
73  double d = std::sin(0.5 * std::atan2(s, c));
74  return 4.0 * d * d;
75  }
76  return 0.0;
77 }
78 
80  UnitVector3d const & v1,
81  UnitVector3d const & v2)
82 {
83  // For the details, see:
84  //
85  // The centroid and inertia tensor for a spherical triangle
86  // John E. Brock
87  // 1974, Naval Postgraduate School, Monterey Calif.
88  //
89  // https://openlibrary.org/books/OL25493734M/The_centroid_and_inertia_tensor_for_a_spherical_triangle
90 
91  Vector3d x01 = v0.robustCross(v1); // twice the cross product of v0 and v1
92  Vector3d x12 = v1.robustCross(v2);
93  Vector3d x20 = v2.robustCross(v0);
94  double s01 = 0.5 * x01.normalize(); // sine of the angle between v0 and v1
95  double s12 = 0.5 * x12.normalize();
96  double s20 = 0.5 * x20.normalize();
97  double c01 = v0.dot(v1); // cosine of the angle between v0 and v1
98  double c12 = v1.dot(v2);
99  double c20 = v2.dot(v0);
100  double a0 = (s12 == 0.0 && c12 == 0.0) ? 0.0 : std::atan2(s12, c12);
101  double a1 = (s20 == 0.0 && c20 == 0.0) ? 0.0 : std::atan2(s20, c20);
102  double a2 = (s01 == 0.0 && c01 == 0.0) ? 0.0 : std::atan2(s01, c01);
103  return 0.5 * (x01 * a2 + x12 * a0 + x20 * a1);
104 }
105 
106 }} // namespace lsst::sphgeom
table::Key< int > b
table::Key< int > a
This file declares a class for representing unit vectors in ℝ³.
T atan2(T... args)
T atan(T... args)
UnitVector3d is a unit vector in ℝ³ with components stored in double precision.
Definition: UnitVector3d.h:55
double dot(Vector3d const &v) const
dot returns the inner product of this unit vector and v.
Definition: UnitVector3d.h:152
Vector3d robustCross(UnitVector3d const &v) const
a.robustCross(b) is (b + a).cross(b - a) - twice the cross product of a and b.
Definition: UnitVector3d.h:161
Vector3d is a vector in ℝ³ with components stored in double precision.
Definition: Vector3d.h:44
double dot(Vector3d const &v) const
dot returns the inner product of this vector and v.
Definition: Vector3d.h:73
double getNorm() const
getNorm returns the L2 norm of this vector.
Definition: Vector3d.h:81
double normalize()
normalize scales this vector to have unit norm and returns its norm prior to scaling.
Definition: Vector3d.cc:41
Vector3d cross(Vector3d const &v) const
cross returns the cross product of this vector and v.
Definition: Vector3d.h:101
T fabs(T... args)
double getMaxSquaredChordLength(Vector3d const &v, Vector3d const &a, Vector3d const &b, Vector3d const &n)
Let p be the unit vector furthest from v that lies on the plane with normal n in the direction of the...
Definition: utils.cc:58
Vector3d getWeightedCentroid(UnitVector3d const &v0, UnitVector3d const &v1, UnitVector3d const &v2)
getWeightedCentroid returns the center of mass of the given spherical triangle (assuming a uniform ma...
Definition: utils.cc:79
double getMinSquaredChordLength(Vector3d const &v, Vector3d const &a, Vector3d const &b, Vector3d const &n)
Let p be the unit vector closest to v that lies on the plane with normal n in the direction of the cr...
Definition: utils.cc:36
constexpr double PI
Definition: constants.h:36
A base class for image defects.
T sin(T... args)
This file declares miscellaneous utility functions.