Euler angles or Tait-Bryan angles or yaw-pitch-roll?
The most intuitive way to describe orientation is through Euler angles. The 3 angles tell about successive rotations about fixed axes. In these free rotations, you can achieve any orientation from every other. There are 12 possible combinations of these rotations. In 6 of them the first and third rotation is performed about the same axis (x-z-x, x-y-x, y-x-y, y-z-y, z-y-z, z-x-z) this convention was introduced by Leonhard Euler and these angles are called Euler angles. The other 6 possible combinations of rotations are about 3 different axes (x-y-z, x-z-y, y-x-z, y-z-x, z-y-x, z-x-y), called Tait-Bryan angles after their creators (these are also sometimes called Euler angles and to make it simpler will be included in this name).
Note that each of these rotations can be performed in the system associated with the object (extrinsic rotations) or in an external, static system (intrinsic rotations). The mutual equivalences are as follows (left - rotations about the internal axes, right - rotations in the external system)
Euler angles:
\begin{gather*} x_1-z'-x_2^{"}\ or\ x_2-z-x_1\\x_1-y'-x_2^{"}\ or\ x_2-y-x_1\\y_1-x'-y_2^{"}\ or\ y_2-x-y_1\\ y_1-z'-y_2^{"}\ or\ y_2-z-y_1\\z_1-y'-z_2^{"}\ or\ z_2-y-z_1\\ z_1-x'-z_2^{"}\ or\ z_2-x-z_1\\ \end{gather*}
Tait-Bryan angles:
\begin{gather*} x-y'-z^{"}\ or\ z-y-x\\ x-z'-y^{"}\ or\ y-z-x\\ y-x'-z^{"}\ or\ z-x-y\\ y-z'-x^{"}\ or\ x-z-y\\ z-y'-x^{"} \ ^*\ or\ x-y-z\\ z-x'-y^{"}\ or\ y-x-z\\ \end{gather*}
$^*$ this set of angles is also call yaw-pitch-roll angles and will be used in my project.
Below you can see how Euler angles work in a real situation:
Euler angles in body frames |
Euler angles in a world frame |
The first picture shows yaw-pitch-roll convention which is commonly used in aviation and aerospace because of the intuitive nature of its movements: at first, the aircraft positions itself on the runway (yaw angle change), then it starts to climb (pitch angle), and finally it adjusts the roll (roll angle). The only difference in the reference system used in aviation, from the one shown in this picture is the sign of the Z-axis. This has its justification, since the aircraft ascends and increases the pitch angle (at Z-axis pointing down). In the case of drones, it is not necessary to raise the "nose of plane" during take-off, so Z-axis directed upwards seems to be more intuitive. In addition, the forward movement of the drone forward involves tilting the front of the drone, which in the assumed reference system increases the angle of pitch. This arrangement seems to be the most intuitive for drones and will be used. To ensure readability of the equations, instead of the angles yaw, pitch, roll will be used greek letters: yaw = $\gamma$, pitch = $\beta$, roll = $\alpha$.
WHERE IS A CATCH?
Gimbal lock in a real situation |
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