Progression Direction (PiG)

Calculates progression direction comparable to Vicon Plug-In-Gait (PiG).

Attributes

Attribute Default value Description Required 
name
 name of the element Yes
 
Position
 position trajectorie,  PiG uses LASI for lower body progession and C7 for upper body progression if no lower body progression exists. Yes

Notes

In Plug in Gait, the lower body Progression Direction is found by looking at the first and last valid position in a trial of the LASI marker. If the distance between the first and last valid position of the LASI marker is greater than a threshold of 800 mm, the X displacement of LASI is compared to its Y displacement. If the X displacement is greater, the subject is deemed to have been walking along the X axis, either positively or negatively, depending on the sign of the X offset. If the Y displacement is greater, the subject is deemed to have been walking along the Y axis, either positively or negatively, depending on the sign of the Y offset.
If the distance between the first and last frame of the LASI marker is less than a threshold of 800 mm however, the Progression Direction is calculated using the direction the pelvis is facing during the middle of the trial. This direction is calculated as a mean over 10% of the frames of the complete trial. Within these frames, only those which have data for all the pelvis markers are used. For each such frame, the rear pelvis position is calculated from either the SACR marker directly, or the centre point of the LPSI and RPSI markers. The front of the pelvis is calculated as the centre point between the LASI and RASI markers. The pelvis direction is calculated as the direction vector from the rear position to the front. This direction is then used in place of the LASI displacement, as described above and compared to the laboratory X and Y axes to choose the Progression Direction.

Following this definition, the Progression Direction in which the subject walks is assumed to be one of four possibilities; Global axes positive X, Global axes positive Y, Global axes negative X or Global axes negative Y and not diagonally to any of these, for example. In Plug in Gait, the upper body Progression Direction is adopted as the same as the lower body's Progression Direction, if it has one. If no lower body Progression Direction has been calculated, an upper body Progression Direction is independently calculated in just the same way as for the lower body. C7 is tested first to determine if the subject moved a distance greater than the threshold. If not, the other thorax markers T10 CLAV and STRN are used to determine the general direction the thorax faces from a mean of 10% of the frames in the middle of the trial. Once the Progression Direction along one of the four possible axes directions is determined, the Progression Frame is defined such that its X axis is oriented positively along this Progression Direction. The Z axis is always assumed to be directed vertically upwards and the Progression Frame is defined following the right-hand rule. The diagram below shows this clearly for each of four circumstances where a subject walks along the different axis directions.

Generated Trajectories

Trajectorie name type Description 


        		

        


        		

        


        		

      


    
  






Notes




<name>is the value of the elements name attribute.


  



Examples




  
<GaitProgressionDirection name="GaitProgessionDirectionPiG">LASI</GaitDirecxtionProgression>