Before you begin, ensure you have downloaded the 6_DOF_Model data as described in About the model for this tutorial.
Start ProCalc, and on the Data Management tab, navigate to the 6_DOF_Model folder and double-click the trial called Static to load it.
The markers from the static trial are displayed in the 3D workspace:
To toggle the display of all the labels, select the option at the top right of the workspace, or press CTRL+SPACE.
To define the static model:
- At the top of the Variables tab, click the Create button , to create a new scheme. Name it appropriately, eg, 6DOF Shoe Model, and press the Enter key to accept the choice.
- At the bottom of the tab, click the Add button
to add a new variable. To define the ankle joint center as the half-way point between the lateral and medial malleolae (LANK and LMMA), do the following:
- In the text box for the variable's name, type LAJC.
- For the Function group, select Point and for the function Halfway between A and B.
The A and B drop-downs activate, and the type for these defaults to Point.
- Click on the two malleolae markers in the 3D workspace.
The left ankle joint center is defined.
- Click and to automatically define the right joint center based on what you chose for the left side. For the rest of this tutorial, you can use this trick to define all Right variables, based on already-defined Left ones – in the interests of readability it is not repeated every time.
- Define the foot coordinate system as being aligned with the laboratory coordinate system for the static trial, with origin at the ankle joint center. To do this:
- Click the button again to add another variable.
- Name the variable LeftFootAnatomical.
- Select the Segment group and the function Origin A, X-Axis=B, Z-Axis=B x C.
- Select A=LAJC, B=Lab X-Axis and C=Lab Y-Axis.
The coordinate system is displayed in the 3D workspace.
- Define the foot's technical coordinate system, ie, the one based on the marker clusters only. To do this:
- Click again.
- Name the variable LeftFootTechnical.
- Select Segment and From 3-marker cluster A, B, C.
- Select the three heel cluster markers LHEE_Upper, LHEE_Lower and LHEE_Lateral.
The technical coordinate system is displayed in the workspace – the orientation of this is not important.
- To save the variable scheme, click the button at the top of the tab.
- Click the Parameters tab. Click the Create button to create a new Parameter scheme, name it 6DOF Shoe Model, and press Enter.
Our aim is to calculate the transformation from the technical to the anatomical coordinate system and save this as a parameter, so that the same transformation can be used in the dynamic trial to get the anatomical coordinate system, even if the anatomical markers are no longer present. To do this:
- Create a parameter by clicking the Add button and entering LeftFootAnatomicalToTechnical.
- Select the Average function group and the function Variable A's local coordinates in Variable B [Event A, Event B].
- For the Type select Segment and select LeftFootAnatomical for A, LeftFootTechnical for B, First Valid Frame for Event A and Last Valid Frame for Event B.
Important: Ensure that the Model Parameter check box is selected.
This saves the parameter's value to a file which is subsequently used for the dynamic processing.
- After having defined this parameter for both the left and right sides, make sure that you click the button to save the parameter scheme.