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Consider a right-hand coordinate system, N with basisvectors $\{\hat{x_N},\hat{y_N},\hat{z_N}\}$ where:

  • the x-axis is pointing north
  • the y-axis is pointing east

Consider an airplane with a right-hand coordinate system, B with basis vectors $\{\hat{x_B},\hat{y_B},\hat{z_B}\}$ where:

  • the x-axis is pointing towards the nose of the plane
  • the y-axis is pointing towards the right wing

Looking at an online Euler Angle Visualization Tool it seems that the definition of roll, pitch and yaw of the plane is ?:

  • the N basisvectors are first rotated yaw around the the z-axis
  • the new basisvectors are rotated pitch around the new y-axis
  • the new basisvectors are rotated roll around the new x-axis and the result is the B basis vectors:

$$ \begin{bmatrix} \hat{x_B} \\ \hat{y_B} \\ \hat{z_B} \end{bmatrix} =R_{BN}*\begin{bmatrix} \hat{x_N} \\ \hat{y_N} \\ \hat{z_N} \end{bmatrix} $$ where $$ R_{BN}=RX_{BN}(roll)*RY_{BN}(pitch)*RZ_{BN}(yaw) $$ enter image description here

I find that $$ RZ_{BN} = RZ^T $$ $$ RY_{BN} = RY^T $$ $$ RX_{BN} = RX^T $$ $$ R=RZ*RY*RX=R_{BN}^T $$ where RX, RY RZ and R are the standard rotation matrices used to convert a position from a rotated coordinate system to an unrotated: enter image description here Is this correct?

Next let us assume that roll, pitch and yaw is measured by an instrument (an Inertial Measurement Unit). We introduce a coordinate system for the instrument, I with basisvectors $\{\hat{x_I},\hat{y_I},\hat{z_I}\}$.

The instrument is rotated wrt to the airplane: $$ \begin{bmatrix} \hat{x_I} \\ \hat{y_I} \\ \hat{z_I} \end{bmatrix} =R_{IB}*\begin{bmatrix} \hat{x_B} \\ \hat{y_B} \\ \hat{z_B} \end{bmatrix} $$

Given a known $R_{IB}$ and a measurement from the instrument: $(yaw_i, pitch_i,roll_i)$ how can I find $(yaw, pitch,roll)$ of the airplane?

Andy
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    $$R_{IN} = RX_{IN}(roll_i) * RY_{IN}(pitch_i) * RZ_{IN}(yaw_i)$$ $$R_{BN} = R_{IN} * R_{IB}^T$$ $$pitch = \arcsin(-R_{BN}(2, 0))$$ $$roll = \arctan2(R_{BN}(2, 1), R_{BN}(2, 2))$$ $$yaw = \arctan2(R_{BN}(1, 0), R_{BN}(0, 0))$$ – rumathe Mar 19 '23 at 11:57
  • @rumathe: Should it not be: $roll=arctan2(R(2,1),R(2,2)) = arctan2(R_{BN}(1,2),R_{BN}(2,2))$? – Andy Mar 19 '23 at 12:42
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    You right, mistypo. – rumathe Mar 19 '23 at 12:45

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