imusim coordinate system

[Gregory Allen]

I'm new to this, and here's a really basic question that I've been unable to answer from the tutorial and (seemingly relevant portions of) the documentation.

What coordinate system does IMUSim expect/assume? There are a number of different conventions in use out there.

I'm starting with sampled easting, northing, and altitude, and I want to make a SampledPositionTrajectory. How does IMUSim expect these to be mapped onto x, y, and z?

I also have sampled heading, roll, and pitch, and want to make a SampledRotationTrajectory. I need to use Quaternion.fromEuler, but this also depends on the convention.

Thanks,
-Greg

Gregory E. Allen, PhD, Engineering Scientist
Applied Research Laboratories: The University of Texas at Austin
512-835-3487

[Martin Ling]

Hi Greg,

In general the code assumes a north-east-down (NED) co-ordinate system,
i.e. positive X is north, positive Y is east, and positive Z is down.
We went with this as it is the common convention for aerospace
applications - presumably because the first two axes are
well-established for ground-based co-ordinates and the right hand rule
yields the third. However I always find it a bit counter-intuitive
having altitude be negative.

Note that some of the file formats understood by the simulator have
different conventions, in particular BVH and ASF/AMC files which are
used in animation. These use the common computer graphics co-ordinate
system where positive Y is up and Z is nominally "forwards" for a
character. When reading and writing these formats, the functions
convertNEDtoCG and convertCGtoNED are used internally to map between the
two systems such that "north" corresponds to "forwards".

It would be nice to eliminate the assumption of a NED system from the
code, and where required allow the user to specify the co-ordinate
system to be used explicitly.


Martin