# Quantitative motion analysis

In addition to qualitative analysis techniques, such as the Labanotation and Laban Movement Analysis, there are also numerous methods and technologies for numerical recording of music-related motion, or what is often called "motion capture".

Very generally, we may talk about two main types of technologies: 

- camera-based systems
- sensor-based systems

and each of these have many sub-categories. 

###  Camera-based systems

The great thing about cameras is that they are an easy, fast, cheap and not the least *available* solution to working systematically with the study of music-related motion. Nowadays, everyone has access to high quality video cameras even in their mobile phones, and the cost of professional-quality video cameras is also within the reach for many. 

But in the world of motion capture, there are many other types of camera-based systems beyond regular cameras. There are often two variables that will need to be taken into account: 

1. whether we are using cameras that capture the same thing that we see, or cameras that record for example only infrared light. The latter can for example be very useful if we want to study people dancing in a dark club.

2. whether we are using markers on the body or not. Markers can help identify people or specific body parts in a much more detailed way than a markerless system can. Of course, putting markers on the body makes the whole setup much more complex. 

We are later going to look at demonstrations of how both regular cameras and a more advanced camera-based motion capture system can be used to capture human motion. 

### Sensor-based Motion Capture

The second main type of motion capture systems, is the one built around *sensors*. Here again there are a number of different types of technologies: 

- acoustic
- mechanical
- magnetic
- inertial
- electrical

Common to all of these is that they require to put the sensors on the body of the people to be studied, which makes them less attractive for many musical applications. However, as the technologies are constantly getting smaller, faster and more reliable, they are still very interesting. 

In this course we will demonstrate only one of these systems: the inertial ones. 
 
##  Summary

To summarise, there are a number of analytical approaches and technologies available for studying music-related motion, ranging from: 

- qualitative to quantitative
- cheap to expensive
- small to large
- simple to advanced

It is impossible to give one answer to what type of method or technology to use, they all have their strengths and weaknesses. For that reason it is important to decide on the right analysis method for the question at hand. The perhaps most important factor that should be taken into account is whether to work in a controlled/laboratory setting or in a more ecological setting, such as a concert hall. This will to a large extent guide which methods and tools to use. 

More specialised motion capture systems, like infrared, marker-based systems, electromagnetic systems and various types of inertial sensors, often provide high recording speeds, and high spatial accuracy and precision, but they also come with several drawbacks. Price is one, although such systems have quickly become more affordable. More problematic is that the person being studied has to wear markers/sensors on the body, something that may be both alienating to the performer and obtrusive to the motion being performed. This is particularly problematic when using electromagnetic and mechanical systems with fairly large and heavy sensors and cables. But also the lightweight reflective markers typically used in optical infrared systems are noticed by the performer, albeit to a lesser degree. 

The perhaps biggest challenge with the larger systems is the non-ecological setting they require. Small inertial systems, on the other hand, can be mobile, wireless, and more or less invisible, although the physical sensors need to be placed on the body. So if the aim is to study musicians in a real-world concert situation, plain video recordings may be the only realistic solution.