how to get 6dof data from all rigid bodies in one take?

[frusciante]

hi, i'm pretty much a beginner in this whole mocap thing.

i'm using arena with 16 cams and i would like to have at least 2 rigid bodies in one take (violincello playing movements analysis, violincello plus bow) for exporting in form of 6dof data for easy handling in matlab afterwards. all i can get till now is the 6dof data of only one rigid body (the one that was added first).. where's the clue to get both?
tia
paul

[VincentG]

Do you have a unique point configuration for each rigid body?

Which version of Arena?

[frusciante]

yes, all rigid bodies have unique point configuration and are recognized correctly in recording mode.
all i get in *.bvh seems to be the pivot data of one rigid body.

i will have to check the version of arena tomorrow since it's at my university.

[frusciante]

arena version is 1.5.0000

[frusciante]

ok i found out that there's a radio button ("BVH options") where i can choose which rigid body i want to export.

let's go one step back:

what is the easiest way in arena to export all captured marker-data (of at least two rigid bodies in one take) in order to import the data easily in matlab? it needn't be in realtime. i only get the origin/pivot 6dof data in my bvh-file. then i need to link this origin to all other markers of one rigid body seperately in matlab. this takes time and doesn't seem to be the best way.

any better solution?
do i get the data out of the *.c3d or *.fbx files?

[Seth Steiling]

.c3d will give you actual marker data, with each marker given a label based off of what you name the rigid body(ies) in ARENA. .fbx gives you both marker data and skeleton data, but it is specific to Autodesk applications, so will not suffice for you.

Between .bvh and .c3d, it's often a matter of preference or what your application supports. The former does the solving of the posi/ori data in ARENA, while the latter only solves and labels markers, and leaves the rigid body solving to your final application (where you would group the markers into rigid bodies after importing them via .c3d file).

For your specific purposes, unfortunately ARENA cannot export multiple rigid bodies in a single .bvh file. You would need to export them each individually and then load all of those files into MATLAB. .c3d will get all of the data out, but you will need to confirm that MATLAB can take in labeled markers and define rigid bodies from them. I'm not sure if that is the case. You might be able to find an .fbx importer for MATLAB too, which would be nice, but I'm not familiar with one.

[frusciante]

thanks for now!

i think this matlab toolbox looks nice for importing .c3d files:

https://www.jyu.fi/hum/laitokset/musiik ... captoolbox

btw, can you give me a short summary what do i need the software "tracking tools" for and whether it could be useful in my case? (no person-capturing, but multiple rigid bodies, analysis afterwards)
my university only has the arena software, it may be worth upgrading..?!

[Seth Steiling]

ARENA is primarily for capturing body motion. It includes a skeleton solver, which gives real-time skeleton solving in addition to hierarchical joint angle data via export. It does also do rigid body tracking, and can do so quite well. ARENA has more export options, supporting .c3d, .bvh, and .fbx.

Tracking Tools only tracks markers and rigid bodies. You can't create hierarchical collections of rigid bodies with it. But, it is very optimized for rigid body tracking, with an eye toward low latency for streaming purposes. Where ARENA is intended to be very simple to use, Tracking Tools is intended to open up numerous options for adjusting what the cameras track, how rigid bodies are solved, and how data is processed and streamed. Tracking Tools will save out .c3d and .csv files, but it also has more built in streaming options, with VRPN and trackd support build-in.

For your stated application (rigid body tracking only, for analytical purposes), Tracking Tools seems ideal. It will give you more control over your tracking parameters, and it offers more robust rigid body solving. But, you need to be sure that its methods of data export/streaming will work for you in MATLAB.