Rotation

1 Rotate with aligned axis

• 在3D坐标系下的旋转，可以是以一种分别沿着x-axis, y-axis, z-axis旋转$\alpha$, $\beta$, $\gamma$角度得到各自旋转，然后进行矩阵组合：

  

  

  • python code

  def rotate_with_aligned_axis(alpha, beta, gamma):
      alpha_rad = np.deg2rad(alpha)
      beta_rad = np.deg2rad(beta)
      gamma_rad = np.deg2rad(gamma)
  
      R_x = np.eye(4, dtype=np.float32)
      R_y = np.eye(4, dtype=np.float32)
      R_z = np.eye(4, dtype=np.float32)
  
      R_x[1, 1] = np.cos(alpha_rad); R_x[1, 2] = - np.sin(alpha_rad)
      R_x[2, 1] = np.sin(alpha_rad); R_x[2, 2] = np.cos(alpha_rad)
  
      R_y[0, 0] = np.cos(beta_rad); R_y[0, 2] = np.sin(beta_rad)
      R_y[2, 0] = - np.sin(beta_rad); R_y[2, 2] = np.cos(beta_rad)
  
      R_z[0, 0] = np.cos(gamma_rad); R_z[0, 2] = - np.sin(gamma_rad)
      R_z[1, 0] = np.sin(gamma_rad); R_z[1, 1] = np.cos(gamma_rad)
  
      return np.matmul(R_x, np.matmul(R_y, R_z))
  

2 Rotate with arbitrary axis

• 只是绕着aligned-axis旋转，会存在万向节锁的问题，如果绕着任意axis (vector in 3d) 旋转的话，更加高效。

• 绕任意轴旋转，根据罗德里戈公式（推导过程见旋转之二 - 三维空间中的旋转:罗德里格旋转公式）

  

  • python code

  def rotate_with_arbitrary_axis(axis, theta):
      theta_rad = np.deg2rad(theta)
      axis = axis / np.linalg.norm(axis)
      axis = np.reshape(axis, (3, 1))
  
      N = np.zeros(shape=(3, 3), dtype=np.float32)
      N[0, 1] = - axis[2]; N[0, 2] = axis[1]
      N[1, 0] = axis[2]; N[1, 2] = - axis[0]
      N[2, 0] = - axis[1]; N[2, 1] = axis[0]
  
      R = np.cos(theta_rad) * np.eye(3, dtype=np.float32) + (1 - np.cos(theta_rad)) * np.matmul(axis, axis.T) + np.sin(theta_rad) * N
  
      return R
  

3 Rotate from vFrom to vTo

• 在平常开发中，经常会有需要计算从一个向量vFrom到另一个向量vTo的旋转矩阵的情况，本着拿来主义，这里的公式是：

  

  • python code

  def rotate_vFrom_to_vTo(vFrom, vTo):
      vFrom = vFrom / np.linalg.norm(vFrom)
      vTo = vTo / np.linalg.norm(vTo)
  
      c = np.dot(vFrom, vTo)
      R = np.eye(3, dtype=np.float32)
  
      if np.abs(c - 1.0) < 1e-4 or np.abs(c + 1.0) < 1e-4:
          return R
      
      v = np.cross(vFrom, vTo)
      v_x = np.array([
          [0., -v[2], v[1]],
          [v[2], 0., -v[0]],
          [-v[1], v[0], 0.]
      ], dtype=np.float32)
  
      R += v_x + v_x @ v_x / (1 + c)
  
      return R
  

4 Rotate from one points set to another

• 经典面试问题：给你一堆点集$\mathbf{X}$, 再给你经过旋转、平移变换过后的点集$\mathbf{Y}$, 求从$\mathbf{X}$到$\mathbf{Y}$的旋转和平移。

• 参考论文Least-Squares Fitting of Two 3-D Point Sets, 求解步骤：

  

  • python code

  def compute_transformation(X, Y):
      """
      X -- [N, 3]
      Y -- [N, 3]
      return R|t
      """
      X_mean = np.mean(X, axis=0)
      Y_mean = np.mean(Y, axis=0)
  
      X_hat = X - X_mean
      Y_hat = Y - Y_mean
      s = np.sum(np.linalg.norm(Y_hat, axis=1), axis=0) / np.sum(np.linalg.norm(X_hat, axis=1), axis=0)
  
      A = s * X_hat.T @ Y_hat
      U, _, Vh = np.linalg.svd(A, full_matrices=True)
  
      R = Vh.T @ U.T
  
      t = Y_mean - s * R @ X_mean
  
      return s, R, t
  

5 Code url

• rotation.py

6. Reference

• 旋转之二 - 三维空间中的旋转:罗德里格旋转公式

• 旋转之三 - 旋转矩阵

• SVD的应用

• Calculate Rotation Matrix to align Vector A to Vector B in 3d?

• Least-Squares Fitting of Two 3-D Point Sets

标签：rad,Family,vTo,旋转,几何变换,vFrom,np,Rotation,axis
来源： https://www.cnblogs.com/XiWJ/p/16516020.html