Normalized Joint Angle  Method 2
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Normalized Joint Angle  Method 1 illustrated how to align a Virtual Foot Segment precisely with the Segment Coordinate System for the Shank. The example on this page shows how to create a virtual foot that is aligned with the lab floor. This example uses Tutorial2.cmo from the Visual3D Tutorial Files page. Download this file and follow the steps below.
Open the Tutorial2.cmo file, click on the Model tab. The model has been completely constructed.
Step 1: Create 3 Laboratory Landmarks
The first task is to project the markers that were used to define the foot onto the same plane (for convenience we will use the floor of the laboratory). To do so, we must create some laboratory landmarks.
Click on the Model tab and click on the Landmark Tab. Follow these steps to create these landmarks: Lab_Origin, Lab_X, and Lab_Y.
2. Create Lab_X landmark:

3. Create Lab_Y landmark:

Step 2: Create 3 floor projected foot landmarks
In this step, we will create 3 landmarks (RLA_Floor, RMA_Floor, and RFT1_Floor) that are the projection of the 3 markers used to define the foot (RLA, RMA, and RFT1) onto the floor. We will use the newly created Lab landmarks in Step 1 to project the foot markers on the floor.
1. Create RLA_Floor landmark:

2. Create RMA_Floor landmark:

3. Create RFT1_Floor landmark:

Step 3: Create Virtual Foot Segment Parallel to the Floor
The following method will not set the Ankle Joint Angle to Zero degrees in the standing trial, but it will create a segment coordinate system that is flat to the floor, which is convenient for describing the angle of the foot segment relative to the laboratory, and also produces an ankle joint angle that is close to zero in the standing posture (if the shank is vertical, the angle will be zero).
The following definition will create the Segment Coordinate System for the Virtual Foot Segment aligned parallel to the floor. This can be accomplished by using the projected landmarks just created in Step 2.
Create Right Virtual Foot Segment:

Step 4: Rotate Virtual Foot Segment Coordinate System
Note that the segment coordinate system is parallel to the floor with the zaxis in the plane of the floor rather than vertical (e.g. aligned moreorless with the shank coordinate system). To resolve this, we need to rotate the coordinate system.
Rotate Segment Coordinate System:

The coordinate system is now aligned with zaxis vertical.
Step 5: Plot Angles for Comparison
Let's plot both ankle joint angles (shank with respect to foot and shank with respect to virtual foot) to see the difference.
Create the angles
First, let's create the angles.
Create Right Ankle Angle  Right Foot with respect to Right Shank:

Create the Normalized Right joint angle  Right Virtual Foot with respect to Right Shank:

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Graph the Angles for Comparison
Now let's graph the two angles and compare their signals.
Graph the Right Ankle Angle and Right Ankle Angle Virtual Foot

The top graph represents ankle dorsi/plantarflexion angle. Two signals are shown. The top most signal is right ankle angle and the bottom signal is the normalized angle angle (wrt to virtual foot).
Other Normalization Methods
For another normalization method, go to Normalized Joint Angle  Method 1. In addition, there is a great tutorial Tutorial: Foot and Ankle Angles that discusses normalization.