IMU queation

[Mohammed Elbes]

Hi,

 

Thank you very much for offering this great IMUSIM it is really of great benefit for all researchers in this field.

 

I had a question about the units of the return values of the functions :

 

measurementsAcc = imu.accelerometer.rawMeasurements        ----- is this in m/s^2?

 

measurementsMag = imu.magnetometer.rawMeasurements     ---- whats the unit for this?

 

measurementsGyro = imu.gyroscope.rawMeasurements            ----- is this in radians/second or degrees/second?

 

 

if I am using an IdealIMU, will the calibrated measurements be equal to the calibrated ones?

 

 

Thank you very much,

 

Mohammed

 

 

[Martin Ling]

On Sat, Dec 31, 2011 at 09:52:03PM -0500, Mohammed Elbes wrote:
>
> Thank you very much for offering this great IMUSIM it is really of great
> benefit for all researchers in this field.

Thank you!

> I had a question about the units of the return values of the functions :
>
> measurementsAcc = imu.accelerometer.rawMeasurements ----- is this in m/s^2?
> measurementsMag = imu.magnetometer.rawMeasurements ---- whats the unit for this?
> measurementsGyro = imu.gyroscope.rawMeasurements ----- is this in radians/second or degrees/second?

Accelerations are in m/s^2, magnetic field is in Tesla. These are the SI
units, and IMUSim uses SI units throughout. Angular rates are in radians/second.
This should have been better documented.

> if I am using an IdealIMU, will the calibrated measurements be equal to
> the calibrated ones?

I take it you mean the calibrated measurements will be equal to the raw
ones. If so, yes.

Martin

[MohammedElbes]

Thank you Martin for the quick reply!

I have another question about the asf/amc files from CMU into IMUSIM

These are the headers I have for amc and asf

AMC:

#!OML:ASF H:\Terrain\Patient Classification 1\Walking\steve\steve.ASF
:FULLY-SPECIFIED
:DEGREES
1
root 7.1998 15.3951 -37.2754 6.10139 -3.02043 2.41388
lowerback 1.84522 1.21672 -3.57218
upperback -3.25157 1.48783 0.131133
thorax -4.49007 0.86432 2.05063
lowerneck -10.3665 0.926344 -4.57102
.
.
.

ASF:
# AST/ASF file generated using VICON BodyLanguage
# -----------------------------------------------
:version 1.10
:name VICON
:units
mass 1.0
length 0.45
angle deg
:documentation
.ast/.asf automatically generated from VICON data using
VICON BodyBuilder and BodyLanguage model FoxedUp or
.
.
.

As you notice, the units in the asf file is in deg. my question is,
the IMU gyro output still in radian/second or in deg/second?

Thank you again!
Mohammed

[Martin Ling]

Hi Mohammed,

Sorry, your messages got held up in the moderation queue.

Yes, the gyro output is still in radians/second. The fact that the
ASF/AMC files have angles in degrees is taken care of at the time of
loading the files, when all the rotations given as Euler angles are
converted to the quaternions used in the SampledBodyModel.

After that everything works the same for any SampledBodyModel, no matter
what sort of format it was generated from.

In fact I've just spotted that the ASF/AMC importer code does not
actually check the angle units before conversion, it actually assumes
*all* ASF/AMC files are in degrees. So keep giving it files in degrees,
it will actually do the wrong thing if you give it files in radians.

I've never seen an ASF/AMC file in radians, but there might be some out
there, so that's a bug which should get fixed at some point.

Martin

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