active tracker development at PLF

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leith
Posts: 192
Joined: Tue Jan 02, 2007 2:17 pm

active tracker development at PLF

Post by leith » Wed Jan 03, 2007 4:59 pm

I've been experimenting with my old trackers and some new techniques. I've never used them with natualpoint cameras before, so this was all new to me. I had been using them with standard DV camcorders previously.

I'm using 920nm LEDs that take about 1.5 volts and 50milliamps max. The camera seems to see them fine at this wavelength though I should probably go find some 850nm LEDs to compare.

Using the sanding technique, I've been able to get about 90 degrees of visibility at a distance of about 10 feet. At this distance, both movement speed, and angle of incidence have enough effect as to make the track unreliable outside those parameters.

I have tried an array of 4 LEDs (parallel) closely packed but have the same results. I had hoped that having a tracking area 4x as large, would result in better performance. However, as the array goes off angle, its larger surface area diminishes down to a mere 2x and the LEDs lose their throw. So, no better results for now.

I have tried using the array to light the interior of a particularly thin ping pong ball. However, it appears the LEDs are still too directional, and the ping pong ball does not seem to bounce light around all that well. I got almost identical results in fact.

There are two thing that could be tested at this point, with what I expect to have for the next few weeks. First, I can try an array of non-parallel LEDs where they are tilted out from the center say... 45degrees each. This should help with the incidence issue significantly.

I expect to receive a few samples of some wide throw LED's from Jim. I will need to see how they compare both due to their wider throw, and due to their better wavelength match.

I suspect, that I also need to play with the thresholding and exposure of the camera to find the optimal performance parameters and design. However, I think I'll hold off on that until I have a c:120 rather than these trackir cameras. If nothing else, the ability to see grayscale will help significantly in judging exposure, before thresholding is applied.

This is actually rather promising. If I'm getting 10' without tweaking, then I suspect I'll get much better once everything is sorted out.

-brad

leith
Posts: 192
Joined: Tue Jan 02, 2007 2:17 pm

Re: active tracker development at PLF

Post by leith » Fri Jan 05, 2007 5:49 pm

Jim,

I received the wide throw LEDs today. They look pretty interesting.

Before I start hooking them up to power supplies, I wanted to check with you. What are their specs? What is their min and max voltage. I don't want to burn them out.

thanks.

-brad

Jim
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Re: active tracker development at PLF

Post by Jim » Fri Jan 05, 2007 6:30 pm

Brad:

Yep, I owed you the spec sheet for the LEDs, thanks for the prodding.

http://www.clairex.com/datasheets/cle335_series.pdf

It is safe to assume 1.5V per LED and up to 100ma, but they will light up nicely with 20ma. Remember to use a current limiting resistor!

I am very curious to see what you think of them. They are expensive, about $1 each, but I like them a lot.

We have to get you a C:120 camera soon.

leith
Posts: 192
Joined: Tue Jan 02, 2007 2:17 pm

Re: active tracker development at PLF

Post by leith » Wed Jan 10, 2007 4:18 pm

I only just had enough time to do a preliminary test but I'm very impressed with the LEDs. I was able to get about 170 degrees of visibility total, at a distance of 16 feet. The only reason I stopped at 16, was the wall. I don't know if the angle of incidence falloff is due to the LED emission or simply due to the visibile surface area falling off. I'll run some more extensive and accurate tests later this week. It does seem however, that this LED is more than capable of the task. It has eliminated the angle of incidence and the distance from camera as tracking issues, to the point that the camera resolution is now the limiting factor in capture volume size/usability. And luckily... in the worst of situations, you just add more cameras. So... its looking good.

I'm going to perform more tests and then most likely proceed to final designs for trackers. I'm currious. Do you intend to manufacture active trackers for your system to sell along with your reflective markers? Also, what kind of performance have you been getting from the reflective markers regarding distance and such? Also, the videos posted on the web, of full body mocap, are those reflective or emissive (active) markers?

Thanks again. Those LEDs are great. I think I'm going to be ordering a bunch a couple of weeks from now.

-brad

Jim
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Re: active tracker development at PLF

Post by Jim » Fri Jan 12, 2007 5:30 pm

Brad:

Glad you like the LED, I thought you would!

The sample videos all show passive markers, ones that Yoshi made himself.

We do not plan on offering active markers for sale, but hey, if you make a cool design, and you like how it works, then perhaps I will make them in volume for you? I would rely on what you want for a product, as you are your own customer.

We have not had great distance success with the very small, less than 1/2", markers we are now selling, about 8' is it. We do plan on offering larger diameter markers soon, about 30 days from now, and we also are looking at an updated camera with more IR LEDs.

So, you really don't mind using active markers? I am slightly surprised by that.

leith
Posts: 192
Joined: Tue Jan 02, 2007 2:17 pm

Re: active tracker development at PLF

Post by leith » Fri Jan 12, 2007 5:59 pm

We'll most likely attempt to use both but I suspect the active markers will make up for the hassle at capture time, with better quality tracks at cleanup time.

Obviously for facial we'd go for retro reflective rather than active. But full body is going to be pushing the system pretty hard so I am guessing the active trackers will let us push it farther than reflective.

I actually asked two major vendors out here as to their experience with active trackers and neither of them had ever experimented with them (or so they told me). I was quite surprised. I would think they would have at least considered them, as cleanup continues to be the most time consuming part of the process for vendors and their clients.

At the very least, for tracking rigid bodies live on set (a service one vendor in particular offered as a specialization) I would think an active marker set would help deal with difficult lighting conditions.

Its all an experiment for now. We'll see what works best for us once we've got a system up and running. I'd rather build the active marker set and find its not useful, than never build it at all.

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