anti anti - 3 months ago 23
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


But instead i get:

135,-180,0


Where am i going wrong here?

Answer

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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