number of devices

New project for OpenCap, which is a new software package to estimate 3D human movement dynamics from smartphone videos. OpenCap strongly relies on OpenSim.
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marios giannakopoylos
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Joined: Mon May 13, 2024 8:02 am

number of devices

Post by marios giannakopoylos » Mon Jan 13, 2025 7:25 am

Hey there ! I wanted to ask if there is an optimal number of ios devices for a change of direction tasks (especially 180 degrees ) ? Is there any difference between 2 or 3 for example ? Thanks a lot !

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Matt Petrucci
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Joined: Fri Feb 24, 2012 11:49 am

Re: number of devices

Post by Matt Petrucci » Tue Jan 14, 2025 2:45 pm

Hi Marios,

I would suspect that 3 cameras would be better for this type of collection. 2 could work, but you would probably run into some problems with occlusions.

Hope this helps,
Matt

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Laura Rathmair
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Joined: Tue Nov 05, 2024 2:52 am

Re: number of devices

Post by Laura Rathmair » Thu Jan 16, 2025 6:06 am

Hi,
I wanted to post a follow-up question here:

I have recorded some walking trials with a setup of four iPhones, but I've run into a problem. Two front-facing cameras can see the subject at all times, but as the person enters the capture volume of two cameras, which have been placed viewing the saggital plane, some models are shaky shortly after they enter the latter two cameras. This is not consistent, however- some trials work just fine.
Could this problem occur because the capture volume should be similar for all cameras?

Is there any way to ignore the videos of the two side-facing cameras and just use the two which view the person from the front?

kind regards,

Laura

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Matt Petrucci
Posts: 250
Joined: Fri Feb 24, 2012 11:49 am

Re: number of devices

Post by Matt Petrucci » Tue Jan 21, 2025 1:25 pm

Hi Laura,

In general, the best way to prevent this is to setup your cameras such that the person starts and ends within the cameras at all time. https://www.youtube.com/watch?v=LPHeq7bxP38

We don't currently have an option to reprocess in the web app, but if you are able to setup processing locally: https://github.com/stanfordnmbl/opencap ... ne-locally.

Then you can change how many cameras are used https://github.com/stanfordnmbl/opencap ... ics.py#L91 and https://github.com/stanfordnmbl/opencap ... cs.py#L156.

Hope this helps,
Matt

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