filtered Yaw value drifts when use_mag=true about imu_tools

[idryanov]

Hello Mike,

I think you are using the IMU correctly . In my experience, using magnetic
readings indoors almost always to a bad performance, like the one you are
noticing. In my building, for example, all the door frames are metal, and
they are strongly magnetized. Also all the electrical wiring and lab
equipment machines produce strong electromagnetic currents.

In theory, you might be able to get better performance if you pre-filter
the magnetic reading, and only use it to correct when it's orientation and
magnitude look "reasonable". Even then, I'm not sure whether the quality
would be worth the effort.

On Sat, May 18, 2013 at 6:03 AM, Mike [email protected] wrote:

Hi,

I've started using the Xsens MTi-10 IMU for our project. I first use the
ros driver (https://github.com/ethz-asl/ethzasl_xsens_driver) for the imu
to get imu/data_raw and imu/mag published, so that your imu_tools can work.

But when I enabled the use_mag option, the output YAW value (I used tf to
convert your quaternion to RPY) drifts a lot when I move the IMU device
along a straight line, while the ROLL and PITCH values are quite stable.
Also, is the yaw a value relative to the earth north?

Is this an issue that cannot be avoided if the IMU is used indoors? 'cuz
the magnetic measurements are affected indoors?

Of course, if I don't use the mag, the large drift problem of yaw is no
longer there. But a slow accumulated drift is still there. (around 2
deg/min or so).

Please correct me if I'm using any parts in a wrong way...

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/10
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Ivan Dryanovski
The Graduate Center, City University of New York (CUNY)
CCNY Robotics Lab
http://robotics.ccny.cuny.edu/People/Dryanovski

[mickeyxu]

Thanks Ivan!
So, just to wrap up, would you suggest using the filter without fusing the magnetic readings, if placed indoors? In this case, what would you do to the accumulated drift in YAW?
I just want to gather some further ideas, since a drift of 2deg/min seems too large for the usage in my project...

[idryanov]

Yes, I would suggest using it without the magnetic readings.

Drift is a problem with many sensors - IMU, wheel odometers, etc. The
common way to correct that is to use a sensor which can observer the
environment to correct the drift - for example, a camera or a laser.
Algorithms like that fall in the SLAM category (if you don't have a prior
map) or Localization (if you have a map available)

On Sun, May 19, 2013 at 10:40 AM, Mike [email protected] wrote:

Thanks Ivan!
So, just to wrap up, would you suggest using the filter without fusing the
magnetic readings, if placed indoors? In this case, what would you do to
the accumulated drift in YAW?
I just want to gather some further ideas, since a drift of 2deg/min seems
too large for the usage in my project...

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/10#issuecomment-18118641
.

Ivan Dryanovski
The Graduate Center, City University of New York (CUNY)
CCNY Robotics Lab
http://robotics.ccny.cuny.edu/People/Dryanovski

[mickeyxu]

Thanks again!