| // Copyright ©2021 The Gonum Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package r3_test |
| |
| import ( |
| "fmt" |
| "math" |
| |
| "gonum.org/v1/gonum/num/quat" |
| "gonum.org/v1/gonum/spatial/r3" |
| ) |
| |
| // euler returns an r3.Rotation that corresponds to the Euler |
| // angles alpha, beta and gamma which are rotations around the x, |
| // y and z axes respectively. The order of rotations is x, y, z; |
| // there are many conventions for this ordering. |
| func euler(alpha, beta, gamma float64) r3.Rotation { |
| // Note that this function can be algebraically simplified |
| // to reduce floating point operations, but is left in this |
| // form for clarity. |
| var rot1, rot2, rot3 quat.Number |
| rot1.Imag, rot1.Real = math.Sincos(alpha / 2) // x-axis rotation |
| rot2.Jmag, rot2.Real = math.Sincos(beta / 2) // y-axis rotation |
| rot3.Kmag, rot3.Real = math.Sincos(gamma / 2) // z-axis rotation |
| |
| return r3.Rotation(quat.Mul(rot3, quat.Mul(rot2, rot1))) // order of rotations |
| } |
| |
| func ExampleRotation_eulerAngles() { |
| // It is possible to interconvert between the quaternion representation |
| // of a rotation and Euler angles, but this leads to problems. |
| // |
| // The first of these is that there are a variety of conventions for |
| // application of the rotations. |
| // |
| // The more serious consequence of using Euler angles is that it is |
| // possible to put the rotation system into a singularity which results |
| // in loss of degrees of freedom and so causes gimbal lock. This happens |
| // when the second axis to be rotated around is rotated to 𝝿/2. |
| // |
| // See https://en.wikipedia.org/wiki/Euler_angles for more details. |
| |
| pt := r3.Vec{1, 0, 0} |
| |
| // For the Euler conversion function in this example, the second rotation |
| // is around the y-axis. |
| const singularY = math.Pi / 2 |
| |
| arb := math.Pi / 4 |
| |
| fmt.Printf("rotate around x-axis: %.2f\n", euler(arb, 0, 0).Rotate(pt)) |
| fmt.Printf("rotate around y-axis: %.2f\n", euler(0, arb, 0).Rotate(pt)) |
| fmt.Printf("rotate around z-axis: %.2f\n", euler(0, 0, arb).Rotate(pt)) |
| fmt.Printf("rotate around x+y-axes: %.2f\n", euler(arb, arb, 0).Rotate(pt)) |
| fmt.Printf("rotate around x+z-axes: %.2f\n", euler(arb, 0, arb).Rotate(pt)) |
| fmt.Printf("rotate around y+z-axes: %.2f\n", euler(0, arb, arb).Rotate(pt)) |
| |
| fmt.Printf("rotate around y-axis to singularity: %.2f\n", euler(0, singularY, 0).Rotate(pt)) |
| fmt.Printf("rotate around x+y-axes with singularity → gimbal lock: %.2f\n", euler(arb, singularY, 0).Rotate(pt)) |
| fmt.Printf("rotate around z+y-axes with singularity → gimbal lock: %.2f\n", euler(0, singularY, arb).Rotate(pt)) |
| fmt.Printf("rotate around all-axes with singularity → gimbal lock: %.2f\n", euler(arb, singularY, arb).Rotate(pt)) |
| |
| // Output: |
| // |
| // rotate around x-axis: {1.00 0.00 0.00} |
| // rotate around y-axis: {0.71 0.00 -0.71} |
| // rotate around z-axis: {0.71 0.71 0.00} |
| // rotate around x+y-axes: {0.71 0.00 -0.71} |
| // rotate around x+z-axes: {0.71 0.71 0.00} |
| // rotate around y+z-axes: {0.50 0.50 -0.71} |
| // rotate around y-axis to singularity: {0.00 0.00 -1.00} |
| // rotate around x+y-axes with singularity → gimbal lock: {0.00 0.00 -1.00} |
| // rotate around z+y-axes with singularity → gimbal lock: {0.00 0.00 -1.00} |
| // rotate around all-axes with singularity → gimbal lock: {0.00 0.00 -1.00} |
| } |