anti - 1 year ago 77
C# Question

# Find the rotational difference between two quaternions to calibrate two coordinate systems

I need to offset streaming quaternion data by a specific amount. To do this I plan to get the difference between the 2, then offset the first by the second.

I am having trouble finding the difference between the 2.

Using this converter.

I am running this code:

``````public void convertQuat180()
{
Quaternion q = new Quaternion(0.65328f, 0.2706f, 0.65328f, -0.2706f); //45,180,0

Quaternion q180 = new Quaternion(0.70711f, 0, 0.70711f, 0);  // 0,90,0

Quaternion result = q180 * Quaternion.Inverse(q);

Console.WriteLine(result);
}
``````

I would expect
`result`
to be:

``````(euler) diff = 45, 90 , 0
``````

``````135,-180,0
``````

Where am i going wrong here?

What you want is a transformation of coordinate systems. You have a rotation measured by the sensor `RS` and a rotation of the camera `RC`. Both are related by a constant (let's call it) offset `RO`:

``````RS = RC * RO
``````

Or alternatively

``````RC = RS * RO^-1
``````

During your calibration procedure, you acquire `RS` and `RC`. Then, you can calculate the offset as:

``````RO = RC^-1 * RS
RO^-1 = RS^-1 * RC
``````

Just calculate the one that you will use more often (probably `RO^-1` because you want to get the camera rotation from the sensor rotation).

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