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Hi. We're having some issues with our data in Arena, particularly during captures with multiple actors. We have a 24 camera setup. During capture, the data looks solid and we have no drop outs on the skeleton. However, when we reload the data to trajectorize and export, we are getting massive dropouts often across the entire body. It's often quite difficult to even find a single point in the take where all of the skeleton's limbs are correct at the same time.

Capturing a single actor seems far more reliable - our main issue seems to be with multiple actors and with takes where the actor is laying on the floor. We're just having problems figuring out why these takes appear to capture without any drop outs, but have so many when they are reloaded.

Any suggestions would be much appreciated!

Would you be willing to send the .skl files and an example .pt2 or two to support@naturalpoint.com? I can review the data for you and see if I can figure out where the breakage is occuring.

We're trying to get clearance to send some of the data through.

In the meantime, could you clarify whether the playback after capture should match the playback during capture, or is the skeleton position updated on the fly even after being captured?

Even after being captured, when you play back 2D takes (pt2 files), the marker data and skeleton solve are recalculated in real-time, on the fly. This is why we recommend starting every capture in a t-pose, as it gives the skeleton solver a neutral pose to start from. Once you trajectorize the marker data, it is saved as a pt3 file, which bakes in the 3D marker position and labeling. This binds the skeleton to the marker data and no longer requires the solver.

If you are having difficulties, you can always bring up frame 1, and press ctrl-r to reset the skeleton, then use the toolbar above the view window to move the skeleton into place, adjust to proper orientation, then frame forward and backward to set the skeleton to the markers. This will often times help the solver to properly set the skeleton. A video of this being done in Expression can be found here. The concepts are similar in Arena, except instead of a template, you're adjusting a skeleton, so you will have to potentially move the body/head/limbs to get them close enough to the position of the actor. Start by moving the hips into position, then work your way out.

Thanks, that's great - I'll have another look at this early next week and let you know how we get on.

For anyone else with this problem, we're now getting around the issue by trajectorising takes as we capture them during shoots. We find this is the best way to get clean data, but still have the original project files to go back to if required.

Obviously this means extra work during the shoot, but it's totally worth it for the time it saves messing about with data 'on the fly' post capture