Strange "blips" when using FOB

[theuberk]

Hi,

We've been using vizard with the flock of birds (with ERT) hardware for a few months now. Although for the most part it's working well, there are a few things that are happening that seem random and we cannot find the source of. One of these things is strange "blips" that occur sometimes when using the FOB. I've attached a link to a video to show you what I mean:

http://www.youtube.com/watch?v=gFm0TAO81WU

I have a feeling that this may just be some sort of interference by metals in the room, but I can't be sure. Do you know the source of this?

Thanks,
Robin

[farshizzo]

These glitches are most likely caused by your tracking system. Can you provide me with the raw data from the tracker instead of a video? I'm guessing that the magnetic field is being inverted for a frame, and this would be easy to tell if I have the actual numbers coming from the tracker.

[theuberk]

I'm not going to be able to test the hardware until thursday and I don't have the raw data from when the video was taken. I can get this data for you on thursday. If this is the source of the problem, what would be causing this inversion and do you know of any solutions?

[farshizzo]

Are the sensors far away from the ERT when the glitches happen? Keep in mind that the Flock of Birds tracker and other electromagnetic trackers become very jittery and unstable as you move the sensor far from the transmitter. If you need accurate measurements at large distances then you should look into optical tracking systems.

[theuberk]

Distance doesn't seem to be a factor in this particular case. Other strange things do happen when the sensor is far from the ERT but these glitches seem to happen even if the sensor is fairly close to the transmitter.

[theuberk]

Hi,

I just wanted to know if there is some sort of quick cure for the field being inverted. These blips and other strange things that seem like they are coming from the same source as these blips are happening periodically. We need to minimize this as much as possible as it is resulting in skewed data being collected. So, is there anything we can do about this without having to move to optical tracking (not in our budget)?

[mspusch]

did you ever try to move your setup to a different room/space and see if it works there?
also what about cell phones? are you keeping them away? this is all just theory, but I know off a group that has built a whole CAVE out of wood in order to avoid interference.

[theuberk]

We've tried it in three different rooms and these problems have occurred in each of them (one of them being a large open wood floor gym). We actually never thought about cell phones, but that seems like it could seriously effect it. We'll try turning them off. Also, would wood be a good way to block outside interference?

[mspusch]

another option is obviously that there is something wrong with your FOB.
do you get those jumps when you look at just the FOB data?
did you try contacting Ascension about it? Maybe they have seen this problem before.

we have not seen this exact problem before, just in general have seen the FOB be jittery when the sensors are more than 2-3 feet away from the receiver. jitter increases with distance.

as for a fix/workaround, you could intercept the FOB data in Vizard and write an algorithm that ignores sudden large changes by just interpolating and predicting the 'assumed' data for those intervals.
it looks like your 'jumps' are very short, so you would only have to interpolate for a few frames, as after that the data is good again.
there is a good chance that such a workaround will fix your problems well enough so that you can do your experiments without problems.

[theuberk]

Thanks for the quick replies.

Alright, I'll probably end up adding this algorithm, but before I do I want to make sure I absolutely have to. We're going to move all of our equipment (computer, FOB, etc.) farther away from the ERT. I wanted to know if any of the FOB equipment itself (i.e. the part you connect to the computer) could have an effect on the tracking field.

Also, is there any way that a large amount of external, electro-magnetic interference could have an effect on an InertiaCube 2?

Finally, what is the best material to stop electromagnetic waves from passing through it? If there is a very good material, we may be able to put a sort of barrier up between all of our equipment (computer, power cables, power bar, etc.) and the ERT to try to eliminate some interference from the equipment.

[theuberk]

I finally figured out the source of this problem. It was a conflict between the collision detection and the hardware. The hardware was setting the position of the mainview to a position that collided with the ground. Simply turning off mainview collisions fixed the problem.