User's Manual

Document MV0319P.N

MVN User Manual

111

19.6.2 Bony/anatomical landmarks

The positions of bony/anatomical landmarks with respect to the joint origin of the related segment are

presented in the MVNX file, see the <points>tag in the <segment>section. Segments are assumed to

be rigid bodies.

Positions of anatomical landmarks in the global frame (G) can be found by rotating the vector of the

landmark in the body frame (B) to the global frame and adding the global position of the origin.

*G G GB B GB

landmark origin

+ q q  p p x

Or in rotation matrix formulation:

G G GB B

landmark origin

+p p R x

The rotation from body to global (

q) and global position of the origin (

pos) are given in the MVNX file,

see next section.

Figure 67: a) Segment coordinate system at each joint origin, as is used in MVN. b) Joint centers

connected, forming a skeleton Legend: x: red, y: green, z: blue

Note that positions of anatomical landmarks are not measured directly as they are with optical

measurement systems. They are computed using the measured accelerations, angular velocities and

rotations in combination with the biomechanical model. Relevant points are used for the detection of

contacts with the external world and as an indication for scaling of segment lengths.

The MVN character mesh (only for visualization) is an abstract representation of the human skeleton;

therefore not all anatomical landmarks are exactly on the mesh. The ribcage is connected to T8 and will

move accordingly.