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View Full Version : Re: genlocking digital camcorders and software genlock summery



Thomas Seeholzer
11-10-2003, 05:57 PM
Dear list

After reading Young-Hoo Kwon's summary I realized that additional
information might be necessary:

> SIMI computes the timeoffsets at the time of recording.
> I am not quite sure whether they used the software genlock
> method described above or something else.

and

> It appears to me that the software genlock method is the only solution
> for the digital camcorders at the moment.

SIMI-Motion does not use the DLT software genlock as mentioned in Kwon's
mail but it MEASURES the time offset between cameras in the DV signal
arriving at the Firewire port. Since Firewire is a serial bus a single
measurement is not accurate enough, but after a few seconds the data is
reliable with an accuracy of 1 ms.

There are several advantages compared to the DLT software genlock:
- Sync offsets are known immedialtely after stopping the capture process
- DLT computation needs additional information which bring in other errors
(calibration, marker detection etc.)
- No 3D calibration: This makes sense when you want to capture "multiple
2D", e.g. for a simple analysis from both lateral sides, where no common
markers are available and DLT will not be applicable.
- Synchronized data acquisition (EMG, force platforms), where video images
are sometimes used for informational purposes only (no 3D kinematics
needed).

Regards,
Thomas.

Thomas Seeholzer
SIMI Reality Motion Systems GmbH
Tel: +49 89 321459-0
Fax: +49 89 321459-16
Mail: seeholzer@simi.com
Web: http://www.simi.com


> -----Original Message-----
> From: Biomechanics and Movement Science listserver
> [mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of Young-Hoo Kwon, Ph.D.
> Sent: Monday, November 10, 2003 6:04 PM
..
>
> Now back to Kevin's question, I received another email from Thomas
> Seeholzer of SIMI. It sounds like the SIMI system solves this
> problem at
> the time of recording. SIMI computes the timeoffsets at the time of
> recording. I am not quite sure whether they used the software genlock
> method described above or something else.
>
> It appears to me that the software genlock method is the only solution
> for the digital camcorders at the moment.
..
>
> Young-Hoo Kwon
> ------------------------------------------------------
> - Young-Hoo Kwon, Ph.D.
> - Biomechanics Lab, Texas Woman's University
> - kwon3d@kwon3d.com
> - http://kwon3d.com
> ------------------------------------------------------
>

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