How are defined yaw, pitch, roll?

Assuming that the camera is mounted such that the x axis of the camera points towards the right wing, the y axis is pointing towards the tail and the lens is pointing down, the yaw, pitch, roll angles are defined as follows:

Yaw

• If yaw = 0° and the camera is looking to the ground (i.e. nadir), it means that the top of the images points to the north.
• If yaw = 90° and the camera is looking nadir, it means that the top of the images points to the east.
• If yaw = 270 and the camera is looking nadir, it means that the top of the images points to the west.

Pitch

• If pitch = 0, it means that the camera is looking down (i.e. nadir).
• If pitch = 90, it means that the camera is looking forward.

Roll

• If using a gimbal, this value is usually 0.

Some more examples:

• yaw = 0, pitch = 0, roll = 0 means: the camera is nadir (looking down perpendicular to the ground), the top of the image points to the north
• yaw = 0, pitch = 90, roll = 0 means: the camera is looking forward from the drone, towards north
• yaw = 90, pitch = 0, roll = 0 means: the camera is nadir (looking down perpendicular to the ground), the top of the image points to the east

For more information on how to convert yaw, pitch, roll to omega, phi, kappa: How to convert (yaw, pitch, roll) to (omega, phi, kappa)?.