Now we are standing in the music-related motion capture
laboratory here at the Department of Musicology.
And in this lab we are studying music-created body movements
with different types of technologies and methods.
There are different methods when we study music-related body
movement.
We typically work with camera-based systems
and also with sensor-based systems.
And today we're going to show you different types of these
systems-- how we work with them, and how we also analyse
the data.
First, now, we're going to look at one system
that we call an optical marker-based motion capture
system.
And here we have one of these cameras.
We have many of these cameras around the space.
And they each send out infrared light
being reflected on the marker.
Something like this that Christian has on.
So when we work with this, we typically take on a suit,
as we're going to do, and then we work in the space and record
the body movement, and then we analyse it afterwards.
So let's try.
So the idea, now, is that we put these reflective markers
on all the body joints so that we are
able to track them separately.
And then from the front and the back,
it's also important to be able to differentiate
the different sides.
So we typically put, for example, one here,
but also a symmetrical one so it's
possible to see that this is the backside of the body.
This optical motion capture system
is extremely sensitive to motion.
so that means that we need to calibrate it each time we use
it to really get good results.
So this is where my reference system
will be because I record the x, y, and z positions in space.
So there are three axes that we record,
and they are based in this frame.
And then I have this wand with markers on it
and with a very specific length, so it's
possible to measure exactly how good and precise the system is
at any point in time.
So now we are ready to start real recording.
Here we can see all the images from each of the cameras,
and I also have a 3D representation
of the space in question.
And then we are ready to record.
1, 2, 3, go.
And as we see here in this overview,
we get all the dots from all the different cameras,
and then they can be combined into a 3D image like this.
And the nice thing about such a system like we have here,
we're able to move around and look
at the movements of the body from different angles
and perspectives, and even zoom in on details.
So now we're looking at the recording of your movements.
And if I start the playback here,
we can take a look at the different markers.
And the nice thing about such a motion capture system
is that we're able to rotate around and look at this
from different perspectives.
Another thing is that we can also turn on trajectory
so we can actually look at how the movements are changing
over time.
And this also makes it easy to isolate out, say,
the vertical component of movement if we're
interested in that, and also to calculate the velocity
and acceleration rotation.
Let's try to do that.
So we can, for example, take out one of these markers
and look at a plot of the set position, which
is the up and down movement of this particular marker-- where
you can see this repetitive pattern over time
in the up and down moment.
So to try to summarise then, from your experience,
what are the good things about working in a lab like this,
and are there any bad ones?
Well the main advantage of working
with this type of motion capture system
is the high accuracy you get from the recordings.
You're able to record the markers down
to a 0.1 millimetre position, which is state of the art,
really.
And also at very high speeds.
Very high speeds.
Up to 500 Hz is no problem.
Even more is actually possible.
The downside is really that you need a big space
to be able to do it-- preferably a fixed location
where the motion capture system can be attached because it
takes a long time to set it up, and to calibrate,
and also even to put on the suit like this.
So to try to summarise then, this type of motion capture lab
is, in many ways, the best you can do when it comes to getting
very, very good and accurate results,
but if we want to be more flexible when we work
with music-related body movement,
we need to use other techniques.