Motion capture, also known as mocap, has become an essential tool in sectors such as sports, healthcare, and industry. It allows analyzing how the body or objects move, providing key information to improve performance, optimize processes, and prevent injuries.
There are two main technologies for motion capture: inertial measurement unit (IMU)-based systems and optical camera-based systems. Although both aim to record movement accurately, they do so in very different ways. In this article, we explain their characteristics, advantages, limitations, and use cases to help you decide which one is best suited to your needs.
IMU systems: inertial sensors
IMU systems consist of small sensors that include accelerometers, gyroscopes, and magnetometers. These sensors are placed at strategic points on the body, either via suits, straps, or adhesives, and record movement in real time.
How they work
Each sensor measures changes in the acceleration and orientation of the body part on which it is mounted. By combining the data from all the sensors, the software reconstructs a three-dimensional model of the complete movement. They don’t require cameras or a controlled space.
Advantages
Portability: they can be used anywhere, whether on a soccer field, in a gym, or in a small clinic.
- Quick installation: sensor placement is simple and requires no complex calibrations.
- Affordable cost: in general, IMU systems are more economical than optical ones.
- Independence from visibility: the sensors continue to function even if some body parts are obscured.
Limitations
- Lower absolute accuracy: although adequate for training and clinical use, it does not match the accuracy of optical systems.
- Accumulated drift: in long sessions, the sensors can accumulate small deviations.
- Dependence on correct placement: improper alignment can affect data quality
Optical systems: 3D cameras
Optical systems use multiple high-speed cameras that capture movement from different angles. Reflective markers are placed on the body, or markerless systems are used to reconstruct the body’s 3D shape and position.
How it works
The cameras simultaneously record the position of the markers or the body, and the software combines the different perspectives to generate an accurate three-dimensional model.
Advantages
- High precision: optical systems provide extremely reliable and detailed results, suitable for scientific research and clinical analysis.
- Reproducible results: allow movements to be compared over time with great accuracy.
- Widespread use in film and video games: it is the preferred technology for high-quality animations.
Limitations
- High cost: both the hardware and installation require a significant investment.
- Need for a controlled environment: they require a laboratory or room that is equipped and calibrated.
- Occlusion issues: if the markers are not visible to the cameras, the capture may be affected.
System comparison
| Feature | IMU (Inertial Sensors) | Optical (3D Cameras) |
|---|---|---|
| Precision | Good, suitable for sports and outpatient clinic | Very high, laboratory standard |
| Portability | High, can be used in any environment | Limited, requires fixed installation |
| Cost | More economical | More expensive |
| Infrastructure | Portable sensors without cameras | Multiple cameras and calibrated room |
| Installation time | Minutes | Hours |
| Ideal applications | Sports training, mobile clinics, flexible industry | Gait Labs, clinical research, film, animation |
When to use each system
- Optical systems: ideal when maximum precision is required in a controlled environment, such as hospitals, gait analysis laboratories, or research studies.
- IMU systems: suitable when portability and flexibility are paramount, for example in sports training, outpatient rehabilitation, or motion analysis in an industrial plant.
- Combination of both: in some cases, combining IMU and optical systems allows leveraging laboratory precision and field mobility, offering a comprehensive approach.
The choice between IMU and optical systems depends on the specific needs of each user or project. IMUs offer mobility and ease of use, while optical systems provide maximum precision and detail. Understanding the characteristics of each technology makes it easier to choose and allows motion capture to be optimised for the objective, whether it’s improving performance, analysing patients’ gait, or controlling industrial processes.
If you’d like to evaluate which motion capture system best suits your needs, you can request a demonstration from STT Systems, and our team will advise you on the most appropriate solution for sports, healthcare, or industry.