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Choosing an appropriate camera arrangement

When planning a new motion capture session, it is important to consider how to place your cameras.
OK. So we are doing a bit of different setups and different kind of recordings. And so what kind of recordings are you doing, Laura? Well, we’ve just been working on recordings of the string quartet. So in this case, we’re capturing the motion both of the musicians, for musicians, and at this point I was looking at their bow movements. And sometimes also the movements of their instruments. So what did you think when you were planning for placing the cameras in this setting? Yeah. It’s actually quite a complex setup with four musicians because well you have the musicians in their chairs, and their music stands, and their bows. And everybody is moving all the time.
So there’s a lot of possible sources of occlusion. Yeah. So it’s likely that the cameras are going to be blocked. The view of the markers are going to be blocked at some point. So you have to very strategically place the cameras at very different angles to make sure that you’re capturing every part, so capturing all around the four musicians, but then getting different angles so that when they move, the view of the markers will not disappear. So how many cameras should capture each marker at each time do you think ideally? At least two cameras. But ideally, you would like perhaps three or four, given that the musicians are going to be moving quite a lot. Exactly.
And what have you been looking to capture? Yeah. So I’ve been doing recordings of both musicians and dancers. And my dancers are really moving about. So first of all, I need quite a large space. And also, my cameras are placed at different heights. And also one thing to think about when you do recordings with dancers is that you have to remember that they may also move higher than the head if they have their hands up in the air. So that is also something that one have to remember when you place the cameras. Have you done something similar? I have with piano duos. In this case, we had two grand pianos that were facing each other.
So that the pianists were looking straight at each other across the two. So this meant that the two pianists were the length of two grand pianos apart from each other. And this is in kind of a constrained space. So it was necessary to cluster the cameras around the two musicians, four cameras and four cameras in that case, and make kind of two sub capture volumes. Cool.
So can you tell me why you have used this particular type of camera? So the reason why I used, or actually I used several systems. But I also used this one for capturing in the field. Because they are quite small. And but works very well I think. And they’re light and quite easy to put up. Yes. Yes, I’ve also used these outside of the lab. And it is quite easy to capture, actually, quite a large area even if they are very small. And when you set up your experiments, do you use this kind of thing, or do you use tripods? I use both.
But I use tripods as well because in some of the rooms that I’ve been, there it’s not really, yeah, anything else to attach them to. That works well as well. The only thing that you have to make sure is that the four is really stable. Because and also with the dancers, that the dancers don’t come so close. Because then they can start to move. And then it doesn’t work. So if there’s many people dancing, then the floor moves. Yeah, sometimes. So that is something to be aware of if you’re using tripods.

When planning a new motion capture session, it is important to consider how to place your cameras. Sometimes a creative camera arrangement is necessary to capture all of your markers well.

In this video, Laura and Mari discuss how to set up cameras for different capture scenarios. They explain some of the camera arrangements that they have used in their research. A few important questions are addressed:

  • How do you arrange cameras when capturing full-body motion, which has some very high markers (heads) and some very low markers (feet)?
  • How do you arrange cameras if your subjects will be placed far apart?
  • Why should you be careful about placing cameras on tripods?
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Motion Capture: The Art of Studying Human Activity

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