3D Motion Capture of 6 objects

fanky

Hi,
I have been motion tracking six "lamps" in a wave pendulum for a large stage construction (see link) with one camera from above. Now we would like to develope the project and make a 3D tracking, where each lamp also get tracked at all time. Is there any affordable MoCap solution out there to do this. Im athinking of the following:

Inertial tracking would be great, and we can attach sensors to each lamp. I can though see a problem in that the lamps are rotating, which might be a bad thing for the sensors?

Optical solutions for 3D tracking, is there any that are affordable at aprox 1000 - 3000 dollar?

Example of the stage and lamps/pendulums:
https://youtu.be/x_o1wvVqMb0

Fred

@fanky most optical tracking systems that can handle that much movement speed and space are going to cost 10 times that budget. One experiment that might be interesting and cheap is to buy a joystick controller, open it and remove the springs that pull the joystick back to center and try attach the top of the cable (where it is mounted to the truss) to the joy stick. If it does not interfere with the movement too much it will give you an xy angle of the lamp cable, when you know the length of the cable this can let you calculate the position in 3d space.

Other than that you could try to use trackers from an HTC vive set, these are a bit heavy and this would require some work, but you can use the vive system without a headset (https://vvvv.org/blog/using-ht...) they are a bit of a pain to use but give fast and accurate positions in 3d space. This could come in your budget but would also be a bit of a pain to run and setup.

fanky

Thanks @fred for your input, i know you have great experience in this field!

2D tracking is already solved with a Allied Vision Guppy camera which works excellent, and since the artist is doing arial tricks flying in the "lamps" the joystick aproach wont work :-).

If the budget would be able to stretch a lot - maybe 10 times as you suggest, what kind of system do you think would be the best option for this kind of tracking?

Woland

@fanky

https://blacktrax.cast-soft.com/

mark_m

@fanky

I don't have a solution for you, but just to say that I love this kind of work! I've worked a lot with jugglers, and have been fascinated by the progress of pendulum, or horizontal, juggling since the application of Siteswap notation to the work. Would love to see what you're doing visually with this work. Will you let me know any performance dates, or a link to the company website? Thanks!

Fred

@fanky the cheapest solutions are from optirack https://optitrack.com/ you

could maybe do this with an 8 camera system, but each bulb would need a rigid body or active marker.

The blacktrack system that @Woland mentioned is just repackaged optirack hardware and software with an extra layer of software over the top. No extra functionality and way more expensive. Not sure why it gets press but it does have some kind of integration with expensive media servers. The cameras and the software are generally lagging behind what optirack actually has.

The optirack site has a kind of system builder to see what kind of system for what kind of space you might need. You would be looking at upwards of 20k and then you need to work out a way to tour it, flight cases, setup time etc.

Due to the fact that you will need markers you could take a good look at an HTC vive pro with trackers, it is really a viable solution and very accurate.

Watching the video a bit more, I don't see how adding some kind of small X/y joystick to where the lamp cables are mounted would get in the way of anything. The lamps would not have to strain on it, just have it move with the cables.

Fred

Woland

@fred said:

The blacktrack system that @Woland mentioned

I mention BlackTrax because we have native support for it in Isadora 3 now.

Fred

@woland aha, well for posterity here is an app that will convert optitrack natnet output to osc and has a format designed to work with isadora.

https://github.com/tecartlab/a...

Woland

@fred said:

@woland aha, well for posterity here is an app that will convert optitrack natnet output to osc and has a format designed to work with isadora.

@mark Native plugin time?

Fred

@woland out of curiosity, how does the native black trax work? I don't see an actor in version 3. One of my main questions for with of these integration is Isadora's ability to deal with 3d positions, AFAIK there is no Quaternion or 4x4 Matrix support so moving things around in 3D means using Euler angles and positions that are pretty limited. As there are already a bunch of bridges available for these tracking systems, I would say that native plugins would not be a priority, but better 3d orientation would be really cool.

Woland

@fred said:

I don't see an actor in version 3.

We've got a plugin that Mark demo'd at the Werkstatt. We're in the process of creating documentation and a demo video/file for it.

@Fred said:

out of curiosity, how does the native black trax work?

Steam power? Not sure, Mark is the brains of the operation.

@Fred said:

better 3d orientation would be really cool

Certainly a tall order, but duly-noted.

@Fred said:

I would say that native plugins would not be a priority

When they're easy to make, adding native plugins to the program is a good way for us to simplify workflow for our users, so for us it sometimes is a priority. Also, having a native plugin instead of presenting workflows to our users that necessitate the use third-party software means we're more in control and less likely to have the "standard" way of interfacing X system with Isadora break because other software that was required no longer functions properly.

barneybroomer

One problem you might run into capturing this stage in real time is the distance from the Optitrack camera's to the play field. The lightbulbs travel to the outer corners of a theatre, so keep in mind if you want to track it good the camera's also need a distance to track it right. Maybe the the lightbulbs can be outfitted with IR emitters as well, and track those with IR cams in XYZ cam with IR filter instead of emitting the whole area with IR and track the bulbs.

DusX

Watching the video, I think I most like Freds Idea of tracking the original angle and calculating the position.
It won't be exact, since the power cords bend at times, but it seems like it has the potential of being pretty good, and could be achieved for a relatively low cost.
Not sure what other hardware aside from Joysticks would help with this approach, but I think its worth some consideration.

DusX

@fred said:

AFAIK there is no Quaternion or 4x4 Matrix support

not natively, but JS support can be achieved by loading appropriate libraries. (a quick search turned some up, I haven't need to use any myself so I can't make a recommendation)

Fred

@dusx yes, I have done this, libraries are not needed to do the maths, but on the end we can only draw with Euler.