# Normalized Joint Angle - Method 1

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One method for setting the Ankle Joint Angle to Zero degrees in the standing trial is to define the Segment Coordinate System for the Virtual Foot Segment to be aligned precisely with the Segment Coordinate System for the Shank. This can be accomplished by using the same proximal and distal targets.

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: Construct Right Shank Segment

Create Right Shank Segment:

1. In the Segments tab, from the Segment Name pulldown select Right Shank.
2. Click on the Create Segment button.
3. In the Right Shank tab, enter these values:
 Define Proximal Joint and Radius    Lateral: RLK     Joint: None     Medial: RMK         Radius: numbers grayed out    Define Distal Joint and Radius    Lateral: RLA     Joint: None     Medial: RMA         Radius: numbers grayed out    Extra Target to Define Orientation    Location: None     None    Select Tracking Targets:      Check RSK1, RSK2, RSK3, RSK4
4. Click on Build Model. A 3D image of the shank will appear
5. Click on Close Tab before proceeding.

## Step 2: Construct Right Virtual Foot Segment

Create Right Virtual Foot Segment:

1. In the Segments tab, type Right Virtual Foot in the Segment Name box.
2. Check Kinematic Only
3. Click on the Create Segment button.
4. In the Right Virtual Foot tab, enter these values:
 Define Proximal Joint and Radius    Lateral: RLK     Joint: None     Medial: RMK         Radius: numbers grayed out    Define Distal Joint and Radius    Lateral: RLA     Joint: None     Medial: RMA         Radius: numbers grayed out    Extra Target to Define Orientation    Location: None     None    Select Tracking Targets:      Check RFT1, RFT2, RFT3
5. Click on Build Model. Since it is a Kinematic Only segment, no new image will be appear. Note that the coordinate system for the right virtual foot segment is the same as the right shank segment.
6. Click on Close Tab before proceeding.

Note: that having the two segment coordinate systems perfectly aligned means that the segments have identical orientation in the standing trial and hence have a joint angle of zero degrees.

## Step 3: 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:

1. In the Model menu, select Compute Model Based Data.
2. In the dialog enter the following:
 Data Name    Right Ankle Angle    Model based Item Properties    Joint_Angle    Segment    Right Foot    Reference Segment    Right Shank
3. Click on Create
4. Click on Close before proceeding.

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

1. In the Model menu, select Compute Model Based Data.
2. In the dialog enter the following:
 Data Name    Right Ankle Angle Virtual Foot    Model based Item Properties    Joint_Angle    Segment    Right Virtual Foot    Reference Segment    Right Shank
3. Click on Create
4. Click on Close before proceeding.
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### Graph the Angles for Comparison

Now let's graph the two angles and compare their signals.