What order are gimbal rotations applied in? Along what reference frame?

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Alexander Broekhof

I'm trying to compute gimbal pose based on image metadata. For example, I have this metadata, with the gimbal pointed straight down, traveling south:

```

   drone-dji:GimbalRollDegree="+180.00"
   drone-dji:GimbalYawDegree="+0.70"
   drone-dji:GimbalPitchDegree="-90.00"
   drone-dji:FlightRollDegree="+4.80"
   drone-dji:FlightYawDegree="-180.00"
   drone-dji:FlightPitchDegree="-3.10"

```

In this case, it makes sense to apply the roll first, then pitch, as that will put the gimbal in the intended position. When should yaw be applied? In the order stated here (RYP)? 

Also, I'm interpreting these rotations as being around the fixed NED axes. Is this correct? Or are the rotations applied on the local body frame?

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3 comments

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  • DJI Developer Support
    In this case, it makes sense to apply the roll first, then pitch, as that will put the gimbal in the intended position. When should yaw be applied? In the order stated here (RYP)? -->You can pass in three directions of angles at once and the camera will automatically handle the rotation sequence：Chapter 12: Gimbal and How to change the gimbal attitude? Also, I'm interpreting these rotations as being around the fixed NED axes. Is this correct? Or are the rotations applied on the local body frame? -->I'm not quite sure what coordinate system the metadata stores the values in, the angle passed in by SDK rotating head is using the NED coordinate system. From the data you gave, the values of dji:GimbalYawDegree and dji:FlightYawDegree differ a lot, and the gimbal angle of the metadata should be using the airframe coordinate system.
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  • Alexander Broekhof

    I'm not really concerned with setting the gimbal to a specific pose, but rather recovering the pose at image capture time from the metadata. Through trial and error, I've found that applying the rotations in RPY order achieves the best projection to known ground points, so I'm guessing that might be the correct order. This is using fixed NED axes. 

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  • DJI Developer Support
    If the RPY order can meet your needs, then there is nothing wrong with how you use it. You will get the same effect by using the RPY order and the rotate interface to rotate the head by passing in the angles of the three axes.
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