Ben Stansfield

07-03-2003, 12:56 AM

Dear All,

I am reading the 'ISB recommendations for standardisation in the reporting

of kinematic data' (Wu and Cavanagh, Journal of Biomechanics, vol.28, No 10

pp1257-1261) and am finding it difficult to get the matrix product as given

in the paper (T1g).

>From my reading of the paper the order of rotations that is suggested to get

from one system to another is rotations about Z then Y then X. However, it

appears that the matrix given does the reverse order.

Am I correct in saying that to get from a local reference system to a global

one a rotation about the Z (Rz) followed by one about the Y (Ry) followed by

one about the X (Rx) would be calculated:

[G]=[Rx].[Ry].[Rz][L]=[T1g].[L]

Where:

[L] is the local co-ordinate system location

[G] is the global co-ordinate system location

[Rx],[Ry] and [Rz] are the rotation matrices representing rotations about

the relevant axis.

(note no translation in this example)

The matrix as given in the paper is calculated as:

[G]=[Rz].[Ry].[Rx].[L]=[T1g].[L]

Would this not mean that the first rotation was about the x-axis?

Your's in hope of clarification.

Ben Stansfield

PhD, CEng, MIMechE

Lecturer

Bioengineering Unit

University of Strathclyde, Wolfson Centre

106 Rottenrow, Glasgow, G4 0NW

Tel: ++44 (0)141 548 3031

Fax: ++44 (0)141 552 6098

MSc in Applied Biomechanics by Distance Learning:

http://www.strath.ac.uk/bioeng/pg-info/BioMechDist.htm

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I am reading the 'ISB recommendations for standardisation in the reporting

of kinematic data' (Wu and Cavanagh, Journal of Biomechanics, vol.28, No 10

pp1257-1261) and am finding it difficult to get the matrix product as given

in the paper (T1g).

>From my reading of the paper the order of rotations that is suggested to get

from one system to another is rotations about Z then Y then X. However, it

appears that the matrix given does the reverse order.

Am I correct in saying that to get from a local reference system to a global

one a rotation about the Z (Rz) followed by one about the Y (Ry) followed by

one about the X (Rx) would be calculated:

[G]=[Rx].[Ry].[Rz][L]=[T1g].[L]

Where:

[L] is the local co-ordinate system location

[G] is the global co-ordinate system location

[Rx],[Ry] and [Rz] are the rotation matrices representing rotations about

the relevant axis.

(note no translation in this example)

The matrix as given in the paper is calculated as:

[G]=[Rz].[Ry].[Rx].[L]=[T1g].[L]

Would this not mean that the first rotation was about the x-axis?

Your's in hope of clarification.

Ben Stansfield

PhD, CEng, MIMechE

Lecturer

Bioengineering Unit

University of Strathclyde, Wolfson Centre

106 Rottenrow, Glasgow, G4 0NW

Tel: ++44 (0)141 548 3031

Fax: ++44 (0)141 552 6098

MSc in Applied Biomechanics by Distance Learning:

http://www.strath.ac.uk/bioeng/pg-info/BioMechDist.htm

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To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl

For information and archives: http://isb.ri.ccf.org/biomch-l

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