System and a method for motion tracking using a calibration unit
The invention relates to motion tracking system ( 10 ) for tracking a movement of an object (P) in a three-dimensional space, the said object being composed of object portions having individual dimensions and mutual proportions and being sequentially interconnected by joints the system comprising orientation measurement units (S 1 , S 3 , . . . SN) for measuring data related to at least orientation of the object portions, wherein the orientation measurement units are arranged in positional and orientational relationships with respective object portions and having at least orientational parameters; a processor ( 3, 5 ) for receiving data from the orientation measurement units, the said processor comprising a module for deriving orientation and/or position information of the object portions using the received data and a calibration unit ( 7 ) arranged to calculate calibration values based on received data and pre-determined constraints for determining at least the mutual proportions of the object portions and orientational parameters of the orientation measurement units based on received data, pre-determined constrains and additional input data. The invention further relates to a method for tracking a movement of an object, a medical rehabilitation system and an animation system.
1. A motion tracking system for tracking a movement of an object in a three-dimensional space, the object being composed of object portions having individual dimensions and mutual proportions and being sequentially interconnected by joints, the system comprising:
orientation measurement units for measuring data related to at least an orientation of the object portions, wherein the orientation measurement units are arranged in positional and orientational relationships with respective object portions and having at least orientational parameters;
a processor for receiving data from the orientation measurement units, the processor comprising a module for deriving orientation and/or position information of the object portions using the received data, characterized in that
the processor further comprises a calibration unit arranged to calculate calibration values for determining at least mutual proportions of the object portions and at least orientational parameters of the orientation measurement units based on received data, predetermined constraints and additional input data comprising knowledge about a distance between at least two points and/or knowledge about an acceleration of at least two object portions connected by a joint.
2. A motion tracking system according to claim 1 , wherein the pre-determined constraints comprise geometrical and/or mechanical constraints pertaining to the sequential interconnection of the object portions.
3. A system according to claim 1 , wherein the predetermined constraints are statistically expressed.
4. A system according to claim 1 , the measurement data further relating to the position and/or orientation of the orientation measurement unit, wherein the calibration unit is further arranged to statistically express the parameters of the orientation measurement units.
5. A system according to claim 3 , wherein the calibration unit is further arranged to calculate a statistical error assignable to an individual parameter conceived to be determined.
6. A system according to claim 5 , wherein the calibration unit is further arranged to assign a weighting factor to an individual dimension and/or mutual proportion in relation with the calculated statistical error.
7. A system according to claim 6 , further comprising a control unit arranged to control the processor for discarding measurement data from an orientation measurement unit which provides data used for calculation of a parameter with a reduced weighting factor.
8. A system according to claim 1 , wherein the calibration unit is arranged to use a pre-defined model of the object for determining dimension and/or mutual proportion of the object portions and/or orientational parameters of the orientation measurement units.
9. A system according to claim 8 , wherein the calibration unit is further arranged to use an estimate of parameters of the orientation measurement units.
10. A system according to claim 8 , wherein the individual dimensions and/or mutual proportions of the object portions are a-priori correlated.
11. A system according to claim 1 , wherein the orientation measuring device comprises an inertial sensing unit.
12. A system according to claim 11 , wherein the orientation measurement unit is further assigned with positional parameters, the measurement data comprising acceleration data, measured at least with respect to two points definable of the respective body portions connected by at least one joint, the calibration unit being further arranged to calculate calibration values for determining individual dimensions of the object portions and positional parameters of the orientation measurement units based on received data, pre-determined constraints and additional input data.
13. A system, according to claim 1 , wherein the calibration unit is arranged to operate iteratively.
14. A method for tracking a movement of an object being composed of object portions having individual dimensions and mutual proportions and being sequentially interconnected by joints in a three-dimensional space, comprising:
measuring data related to at least an orientation of the object portions with orientation measurement units, wherein the orientation measurement units are arranged in positional and orientational relationships with respective object portions having at least orientational parameters;
receiving data from the orientation measurement units;
deriving orientation and/or position information of the object portions using the received data;
calculating calibration values for determining at least mutual proportions of the object portions and at least orientational parameters of the orientation measurement units based on received data, predetermined constraints and additional input data comprising knowledge about a distance between at least two points and/or knowledge about an acceleration of at least two object portions connected by a joint.
15. A method according to claim 14 , wherein for the pre-determined constraint knowledge about geometrical and/or mechanical constraints pertaining to the sequential interconnection of the object portions is selected.
16. A method according to claim 14 , wherein the predetermined constraints are statistically expressed.
17. A method according to claim 14 , the measurement data further relating to the position and/or orientation of the orientation measurement unit, wherein the parameters of the orientation measurement units are statistically expressed.
18. A method according to claim 16 , wherein a statistical error assignable to an individual dimension and/or mutual proportion is calculated.
19. A method according to claim 18 , wherein a weighting factor for the individual dimension and/or mutual proportion is assigned in relation with the calculated statistical error.
20. A method according to claim 19 , wherein measurement data leading to a calculation of a parameter with a reduced weighting factor is discarded.
21. A method according to claim 14 , wherein a predefined model of the object is used for determining individual dimensions and/or mutual proportions of the object portions and/or parameters of the orientation measurement units.
22. A method according to claim 21 , wherein an estimate of parameters of the orientation measurement units is used.
23. A method according to claim 21 , wherein the individual parameters of the object portions are a-priori correlated.
24. A method according to claim 14 , wherein the measuring data are obtained using an orientation measuring device comprises, preferably an inertial measurement unit.
25. A method according to claim 24 , wherein the orientation measurement unit is further assigned with positional parameters, the measurement data comprising acceleration data measured at least with respect to two points defined on respective body portions connected by at least one joint, the calibration unit calculating calibration values for determining individual dimensions of the object portions and positional parameters of the orientation measurement units based on received data and predetermined constraints.
26. A method, according to claim 14 , wherein the method steps are carried out iteratively.
27. A medical rehabilitation system comprising the motion tracking system according to claim 1 .
28. An animation system comprising the motion tracking system according to claim 1 .
29. A gaming system comprising a computer and the motion tracking system according to claim 1 .