diff --git a/src/geometry/rotation_specialization.rs b/src/geometry/rotation_specialization.rs index 1ea5cd92..b1ee8c82 100644 --- a/src/geometry/rotation_specialization.rs +++ b/src/geometry/rotation_specialization.rs @@ -979,6 +979,113 @@ impl Rotation3 { ) } } + + /// Represent this rotation as Euler angles. + /// + /// Returns the angles produced in the order provided by seq parameter, along with the + /// observability flag. If the rotation is gimbal locked, then the observability flag is false. + /// + /// Algorithm based on: + /// Malcolm D. Shuster, F. Landis Markley, “General formula for extraction the Euler + /// angles”, Journal of guidance, control, and dynamics, vol. 29.1, pp. 215-221. 2006, + /// and modified to be able to produce extrinsic rotations. + #[must_use] + pub fn euler_angles_ordered( + &self, + mut seq: [Unit>; 3], + extrinsic: bool, + ) -> (Vector3, bool) + where + T: RealField + Copy, + { + let mut angles = Vector3::zeros(); + let eps = T::from_subset(&1e-7); + let _2 = T::from_subset(&2.0); + + if extrinsic { + seq.reverse(); + } + + let [n1, n2, n3] = &seq; + + let n1_c_n2 = n1.cross(n2); + let s1 = n1_c_n2.dot(n3); + let c1 = n1.dot(n3); + let lambda = s1.atan2(c1); + + let mut c = Matrix3::zeros(); + c.column_mut(0).copy_from(n2); + c.column_mut(1).copy_from(&n1_c_n2); + c.column_mut(2).copy_from(n1); + c.transpose_mut(); + + let r1l = Matrix3::new( + T::one(), T::zero(), T::zero(), + T::zero(), c1, s1, + T::zero(), -s1, c1, + ); + let o_t = &c * self.matrix() * (c.transpose() * r1l); + angles.y = o_t.m33.acos(); + + let safe1 = angles.y.abs() >= eps; + let safe2 = (angles.y - T::pi()).abs() >= eps; + let observable = safe1 && safe2; + angles.y += lambda; + + if observable { + angles.x = o_t.m13.atan2(-o_t.m23); + angles.z = o_t.m31.atan2(o_t.m32); + } else { + // gimbal lock detected + if extrinsic { + // angle1 is initialized to zero + if !safe1 { + angles.z = (o_t.m12 - o_t.m21).atan2(o_t.m11 + o_t.m22); + } else { + angles.z = -(o_t.m12 + o_t.m21).atan2(o_t.m11 - o_t.m22); + }; + } else { + // angle3 is initialized to zero + if !safe1 { + angles.x = (o_t.m12 - o_t.m21).atan2(o_t.m11 + o_t.m22); + } else { + angles.x = (o_t.m12 + o_t.m21).atan2(o_t.m11 - o_t.m22); + }; + }; + }; + + let adjust = if seq[0] == seq[2] { + // lambda = 0, so ensure angle2 -> [0, pi] + angles.y < T::zero() || angles.y > T::pi() + } else { + // lamda = + or - pi/2, so ensure angle2 -> [-pi/2, pi/2] + angles.y < -T::frac_pi_2() || angles.y > T::frac_pi_2() + }; + + // dont adjust gimbal locked rotation + if adjust && observable { + angles.x += T::pi(); + angles.y = _2 * lambda - angles.y; + angles.z -= T::pi(); + } + + // ensure all angles are within [-pi, pi] + for angle in angles.as_mut_slice().iter_mut() { + if *angle < -T::pi() { + *angle += T::two_pi(); + } else if *angle > T::pi() { + *angle -= T::two_pi(); + } + } + + if extrinsic { + let tmp = angles.x; + angles.x = angles.z; + angles.z = tmp; + } + + (angles, observable) + } } #[cfg(feature = "rand-no-std")]