The following examples use the markers related to the left shank illustrated below.

1. LMK: Left medial knee
2. LLK: Left lateral knee
3. LSK: Left shank
4. LMA: Left medial ankle
5. LLA: Left lateral ankle
6. LTUB: Left tibial tuberosity (shown projecting a shadow onto the plane)
7. LKJC: Left knee joint centre (landmark)

Landmark_MarkerSet.png{{/images/thumb/9/9e/Landmark_MarkerSet.png/300px-Landmark_MarkerSet.png

The landmark dialog can be broken into 3 sections:

1. Define Orientation
2. Offset
3. Calibration Only

Any time a landmark can be defined using Offsets in three directions, a user has the option to define the offsets manually (X/Y/Z or ML/AP/AXIAL) or they can use the “Offset to Existing Calibration Target or Landmark” option.

When a landmark is set to “Calibration Only” it means that the landmark will only exist in the calibration file. When this option is not checked, it means that the landmark will be created in the associated motion files.

If a landmark is created in the associated motion files, it can be used to track a segment or for other calculations.

Although there are many different ways to define a landmark, all of these methods result in a “virtual marker” whose position is calculated by Visual3D throughout motion trials.

Sample Landmark Definition (click to expand)

Example Using Starting Point (click to expand)

Other Examples:

• Virtual Lab Tutorial: The LAB_O, LAB_X, and LAB_Y landmarks in the virtual lab tutorial are defined in LAB space, where the offsets refer to the distance the landmarks are created in meters.
• The following two examples describe how to define landmarks that represent stair corners. The position of targets placed on the steps are calculated from dynamic trials is used to define the landmarks.
  • Using Motion Trial Example 1
  • Using Motion Trial Example2

Sample Landmark Definition (click to expand)

Other Examples:

• Create a landmark relative to the thigh segment using ML, AP, and AXIAL offsets as percents.
• Creating a landmark at the end of a segment that is tracked with the segment.
• Hip Joint Centers are often defined using regression equations which locate the hip joint centers in the pelvis coordinate system:
  • Bell and Brand Regression Equations
  • Hip Landmark from Custom Regression Equation
• A Knee Alignment Device (KAD) defines the joint centers by defining landmarks in the KAD segment coordinate system
• Create a Landmark Mimicking contralateral segment. This example uses several different types of landmarks, but the end result is a landmark created in the foot coordinate system.

Sample Landmark Definition (click to expand)

Sample Landmark Definition (click to expand)

Create landmark as a midpoint (click to expand)

Sample Landmark Definition (click to expand)

Other Examples:

• Digitized Landmarks are stored and tracked relative to tracking targets
• Functional Landmarks (Joints) are stored and tracked relative to tracking targets
• Muscle insertion points are stored and tracked relative to tracking targets

Landmark Definition (click to expand)

Example 1 (click to expand)

Other Examples:

• Create a Landmark Using two standing trials
  • Example 1
  • Example 2
• Example using a reference location
• Example defining a segment endpoint relative to 3 tracking targets

A target or landmark may be projected onto a line defined by two points.
Landmark_Type3_image.png{{/images/thumb/9/9f/Landmark_Type3_image.png/300px-Landmark_Type3_image.png Landmark_Type3_image_AltView.png]] Landmark_Type5_image_AltView.png{{/images/thumb/b/bd/Landmark_Type5_image_AltView.png/300px-Landmark_Type5_image_AltView.png?300×193]]

Landmark Definition (click to expand)

Example: Project the iliac crest target onto the plane defined by the R/LASIS and RPSIS (click to expand)

Other Examples:

• Project the hip joint onto a plane passing through the GT's
• Example 2: Project onto a principal plane of the lab

Digitized landmarks are defined using a digitized pointer and again result in a “virtual marker” being computed by Visual3D relative to the positions of other, existing markers. The goal of digitized landmarks is to allow users to track anatomical landmarks without having to place markers on that location. See instructions for using a digitizing pointer to learn more.

Functional landmarks indicate the locations of functional joints. Calculating functional joint positions requires movement of one segment relative to another segment. The chosen algorithm then searches for a point (or for a one degree of freedom joint, an axis) that is stationary relative to the 2 segments (or 2 sets of markers).

Visual3D's algorithms for computing functional joint positions are adapted from:

Schwartz MH, Rozumalski A (2005) A new method for estimating joint parameters from motion data. Journal of Biomechanics, 38, 107-116] and from Jensen E, Lugade V, Crenshaw J, Miller E, Kaufman K (2016) A principal component analysis approach to correcting the knee flexion axis during gait. Journal of Biomechanics, in press] See the in-depth explanation of functional joints to learn more.