question about IMU data

[huanhexiao]

Hi authors, thanks for sharing ford avadata. i have som questions about the data:

1. IMU
   I extracted imu.csv from the .bag, whose linear accelaration is as following:
   

It seems too small and far away from gravity measurements 9.8m/s^2.
I've noticed some discussion about the transformation of imu.csv, but i cannot find where the script is.

2. GPS
   According to FordAV home page, "The GPS data provides the latitude, longitude and altitude of the body frame with respect to the WGS84 frame".
   My question is where the origin of the GPS data, body frame(rear axle center) or IMU center?

Could anyone do me a favor please?

[huanhexiao]

@ankitvora7 hi budy, i am confused with the acceleraion data, whether the gravity 9.8m/s^2 was removed from z-axis.
if i want to obtain a real-world data, should i simply add the gravity to z-axis?

[ankitvora7]

Hi @huanhexiao - The IMU data is processed data and as a result gravity is removed. You can add gravity vector after compensating for orientation.
To answer your second question, the origin of GPS data is the body frame.

[huanhexiao]

@ankitvora7 Thanks very much, that's helpful.
Another question, I find that IMU sampling interval is not uniform. Here is some cases:

In addition, there exsists some lost epoch:

[YanhaoZhang]

Hi @ankitvora7 I got the same question. May I know how is the gravity removed from the raw IMU data? Do you use some optimization approaches? If so, could you please provide some more details? Thank you.