Wrong number of markers being detected?

HeroFay
Posts: 17
Joined: Thu Oct 08, 2009 11:10 pm

Wrong number of markers being detected?

Post by HeroFay » Wed Nov 11, 2009 7:47 pm

In Arena software, we were having with the wrong number of markers being detected (39 or 40 instead of 38). And the number keep changing among 38/39/40.

Why this happens and how can we correct or eliminate this problem?

Thanks!

HeroFay
Posts: 17
Joined: Thu Oct 08, 2009 11:10 pm

Re: Wrong number of markers being detected?

Post by HeroFay » Wed Nov 11, 2009 7:48 pm

In addition, besides scaling the height and length of the arms, how important is it to pose the skeleton to match the marker set (i.e. in terms of how it affects the quality of the mocap data collected)?

Many Thanks!

VincentG
Posts: 7728
Joined: Mon Jul 17, 2006 5:00 am
Location: Corvallis, Oregon

Re: Wrong number of markers being detected?

Post by VincentG » Thu Nov 12, 2009 12:02 pm

Are they extra markers being detected near other markers, or from other places within the capture area?

Could they be reflections of reflective material, or jewelry?

What type of results are you getting from the calibration?

How many cameras are you using?

What is your camera setup like?

You want the skeleton to match up with the marker placement, as the points can cause the capture to introduce errors into the data.

HeroFay
Posts: 17
Joined: Thu Oct 08, 2009 11:10 pm

Re: Wrong number of markers being detected?

Post by HeroFay » Thu Nov 12, 2009 12:50 pm

We are using 12 cameras in total, 8 up high and 4 down load. The calibration result says excellent, and I think it is fine.

We observed that, one of the marker on the right shoulder is detected as two in Arena software. Once we remove that one, it shows like 37, but when we put it back, it is like 39/40.

VincentG
Posts: 7728
Joined: Mon Jul 17, 2006 5:00 am
Location: Corvallis, Oregon

Re: Wrong number of markers being detected?

Post by VincentG » Thu Nov 12, 2009 12:53 pm

How much lower are the bottom cameras?

The calibration could be slightly off, even with a reading of excellent.

HeroFay
Posts: 17
Joined: Thu Oct 08, 2009 11:10 pm

Re: Wrong number of markers being detected?

Post by HeroFay » Thu Nov 12, 2009 1:02 pm

The bottom ones are like at 1 meter high positions.

In terms of calibration, this is also what we think would be the cause. This happens when we used the old calibration result, and did not recalibrate again because we believed the camera doesn't move. Is it true that the re-calibration even for slightly change matters a lot?

Thanks in advance!

VincentG
Posts: 7728
Joined: Mon Jul 17, 2006 5:00 am
Location: Corvallis, Oregon

Re: Wrong number of markers being detected?

Post by VincentG » Thu Nov 12, 2009 4:54 pm

Yes, everytime the cameras are moved you need to recalibrate.

The lower cameras should be 2-2.5 feet below the upper cameras. At 1 meter, they are way too low.

CDMoran
Posts: 12
Joined: Tue Aug 25, 2009 9:09 am

Re: Wrong number of markers being detected?

Post by CDMoran » Fri Nov 13, 2009 1:36 am

I had a similar problem when I first started using my system with 6 cameras. With the defualt exposure settings I was getting reflections from the backs of the rigid body hand markers. That was probably made worse by the fact that I have long arms and was working in a non optimal space so my hands were a little closer to the cameras than would be normal. Reducing the exposure setting and moving so that in the T-pose my hands were not lined up with the camreas light source solved the issue.

HeroFay
Posts: 17
Joined: Thu Oct 08, 2009 11:10 pm

Re: Wrong number of markers being detected?

Post by HeroFay » Fri Nov 13, 2009 2:19 pm

How important are the calibrations of cameras/skeleton affecting to overall mocap quality? Is there any metric to measure it?

Asking this question is because I usually see some errors happened and the character in Arena has wrong joints (in red color during mocap) in places. So, I really wonder how to do with this error.

Thank you very much.

VincentG
Posts: 7728
Joined: Mon Jul 17, 2006 5:00 am
Location: Corvallis, Oregon

Re: Wrong number of markers being detected?

Post by VincentG » Fri Nov 13, 2009 2:27 pm

Yes, a bad calibration, or skeleton marker placement can gratly effect the data quality that you get..

You can send copies of your calibration, t-pose file - skl file, and some captured pt2 data to support.

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