This page shows the coordinate system used in the Crazyflie® 2.x family.
The global coordinate system (X, Y, Z) is a fixed, right-handed frame. Its origin and orientation are established at initialization. How they are established depends on the setup:
- With external positioning (e.g. Lighthouse, mocap, UWB): the frame is defined by the positioning system’s calibration - including which way each axis points. Recalibrating the positioning system redefines the frame.
- Without external positioning (dead reckoning from optical flow / IMU): the drone’s initial position sets the origin and its heading sets the direction of global X. Roll and pitch are not inherited. Global Z is aligned with gravity (Z-up). Starting on a slope does not tilt the global frame.
The body coordinate system (x, y, z) is right-handed with x-forward, y-left, z-up.
The orientation of the body frame relative to the global frame is described by roll, pitch, and yaw (φ, θ, ψ). Each is a rotation about one body axis:
- roll (φ) is a rotation about the x-axis
- pitch (θ) is a rotation about the y-axis
- yaw (ψ) is a rotation about the z-axis
Applied in the ZYX order: yaw first, then pitch, then roll. The angles are not independent - the same three values applied in a different order describe a different orientation.
Viewed from the origin looking outward along the positive axis:
- roll (φ) is positive clockwise - a positive roll drops the drone’s right side.
- pitch (θ) is positive counter-clockwise - a positive pitch raises the drone’s nose.
- yaw (ψ) is positive clockwise - a positive yaw turns the drone’s nose to the left.
Note: pitch runs counter-clockwise only in the reported Euler angles - the estimator’s quaternion treats it clockwise, like roll and yaw, so the pitch it encodes has the opposite sign to attitude.pitch; negate the pitch when converting between the two, in either direction.
