Discussion:
[Rock-dev] Standard unit for IMU mangetometer values?
Leif Christensen
2014-07-07 12:47:25 UTC
Permalink
Hi,

do we have a standard unit / convention for magnetometer readings?

In the xsens_imu and imu_xsens drivers, we are just forwarding the
values from the xsens, which confirms to no standard at all (arbitrary
unit with 1 being the magnetic field strength at calibration time in
Enschede, Netherlands). The stim300, imu_kvh_1750 have no magnetometer
inside.

Some are using Tesla, some Gauss (10^-4 T).

Most of the time we are interested in the magnetic flux density of the
(distorted) earth magnetic field, which ranges from 30?T (equator) to 60
?T (pole).

Apart from being the derived SI unit, Tesla is a little bit unhandy for
these ranges, I think. But if we have a standard there, I would go with
that. If not, I would either propose ?T or Gauss.

Total magnetic field strength today in Bremen (IGRF11 model):
49429.8 nT
49.4298 ?T
0.494298 G
0.0000494298 T

LG,
Leif
--
Leif Christensen

DFKI Bremen
Robotics Innovation Center
Robert-Hooke-Stra?e 5
28359 Bremen, Germany

Phone: +49 (0)421 17845-4149
Fax: +49 (0)421 17845-4150
E-Mail: leif.christensen at dfki.de

Weitere Informationen: http://www.dfki.de/robotik
-----------------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Stra?e 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.: DE 148646973
Steuernummer: 19/673/0060/3
-----------------------------------------------------------------------
Steffen Planthaber
2014-07-07 13:07:21 UTC
Permalink
Hi,

As you mentioned we decided for SI units and we should stick to that.

As the value is a float anyways, I can't see any advantages in moving
from SI as "tansport unit".

Nevertheless it is unhandy. So I'd use the SI unit and add a getter
methods "toNanoTesla()" to get readable values (according to
base/time.toMilliseconds())

This way, the use of a non-SI unit is clearly visible in the source code.


Steffen
Post by Leif Christensen
Hi,
do we have a standard unit / convention for magnetometer readings?
In the xsens_imu and imu_xsens drivers, we are just forwarding the
values from the xsens, which confirms to no standard at all (arbitrary
unit with 1 being the magnetic field strength at calibration time in
Enschede, Netherlands). The stim300, imu_kvh_1750 have no magnetometer
inside.
Some are using Tesla, some Gauss (10^-4 T).
Most of the time we are interested in the magnetic flux density of the
(distorted) earth magnetic field, which ranges from 30?T (equator) to 60
?T (pole).
Apart from being the derived SI unit, Tesla is a little bit unhandy for
these ranges, I think. But if we have a standard there, I would go with
that. If not, I would either propose ?T or Gauss.
49429.8 nT
49.4298 ?T
0.494298 G
0.0000494298 T
LG,
Leif
--
Steffen Planthaber
Weltraumrobotik

Besuchsadresse der Nebengesch?ftstelle:
DFKI GmbH
Robotics Innovation Center
Robert-Hooke-Stra?e 5
28359 Bremen, Germany

Postadresse der Hauptgesch?ftsstelle Standort Bremen:
DFKI GmbH
Robotics Innovation Center
Robert-Hooke-Stra?e 1
28359 Bremen, Germany

Tel.: +49 421 178 45-4125
Zentrale: +49 421 178 45-0
Fax: +49 421 178 45-4150 (Faxe bitte namentlich kennzeichnen)
E-Mail: Steffen.Planthaber at dfki.de

Weitere Informationen: http://www.dfki.de/robotik
-----------------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Stra?e 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.: DE 148646973
Steuernummer: 19/673/0060/3
-----------------------------------------------------------------------
Sylvain Joyeux
2014-07-07 18:52:38 UTC
Permalink
On Mon, Jul 7, 2014 at 3:07 PM, Steffen Planthaber <
Post by Steffen Planthaber
As you mentioned we decided for SI units and we should stick to that.
As the value is a float anyways, I can't see any advantages in moving
from SI as "tansport unit".
Nevertheless it is unhandy. So I'd use the SI unit and add a getter
methods "toNanoTesla()" to get readable values (according to
base/time.toMilliseconds())
This way, the use of a non-SI unit is clearly visible in the source code.
+1

Sylvain
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Jan Christian Albiez
2014-07-07 18:57:20 UTC
Permalink
SI, always SI!!

If necessary with class/macros/functions for derivative units, but all transfer in SI.

SI is one of the french inventions, that really does make a lot of sense! 8)

blue skies
Jan
Post by Steffen Planthaber
As you mentioned we decided for SI units and we should stick to that.
As the value is a float anyways, I can't see any advantages in moving
from SI as "tansport unit".
Nevertheless it is unhandy. So I'd use the SI unit and add a getter
methods "toNanoTesla()" to get readable values (according to
base/time.toMilliseconds())
This way, the use of a non-SI unit is clearly visible in the source code.
+1
Sylvain
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Dr. Jan Christian Albiez
Senior Researcher - Brasilian Relation

DFKI Bremen
Robotics Innovation Center
Robert-Hooke-Stra?e 1, 28359 Bremen, Germany

Zentrale: +49 421 178 45 0
Email: jan.albiez at dfki.de

Further Information: http://www.dfki.de/robotics
----------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Stra?e 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.: DE 148646973
Steuernummer: 19/673/0060/3
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Leif Christensen
2014-07-08 09:09:53 UTC
Permalink
Post by Jan Christian Albiez
If necessary with class/macros/functions for derivative units, but all transfer in SI.
Unfortunate wording. Derivative SI units should definitely be ok. You
don't want to stick to SI basic units and express your battery voltage
in m^2*kg*s^-3*A^-1 but in Volt.

So I will stick to Tesla for magnetometer readings (and not kg?s^?2?A^?1).

So long,
Leif
--
Leif Christensen

DFKI Bremen
Robotics Innovation Center
Robert-Hooke-Stra?e 5
28359 Bremen, Germany

Phone: +49 (0)421 17845-4149
Fax: +49 (0)421 17845-4150
E-Mail: leif.christensen at dfki.de

Weitere Informationen: http://www.dfki.de/robotik
-----------------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Stra?e 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.: DE 148646973
Steuernummer: 19/673/0060/3
-----------------------------------------------------------------------
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