When conducting a custom test with your HumanTrak system, you have the ability to take custom measurements – lengths and angles – directly on a test snapshot. Even though a snapshot is a 2D image, HumanTrak automatically scales your measurements so they reflect the real-world length. This useful tool can help you calculate limb length, distances between points/objects, or metrics involving specific angles.
How HumanTrak calculates length
Finds the right depth
Each snapshot is linked to a specific limb or side (e.g. left leg). HumanTrak uses the depth (z-value) of that limb – or the centre of mass for full-body views – to determine how far the measurement plane is from the camera.
Creates a virtual measurement plane
The system constructs a flat 2D plane at the same depth as the abovementioned z-value. This plane acts like a transparent sheet in space, perpendicular to the camera, on which your line or angle is drawn.
Measures using real-world scale
When you drag two points on this 2D plane, HumanTrak calculates the straight-line distance in pixels and then converts it into centimeters. It factors in field of view and depth to ensure the result reflects real-world scale, no matter the direction of measurement.
Calculate image-based measurements
To measure a custom angle or length, you will need a custom test created with an angle or length metric attached.
Follow the steps to run your custom test with an individual. After taking a snapshot at the desired position, you will be able to calculate an angle or length directly on the image.
Measure custom angles 
Click and drag the three points in turn to measure the angle from the common point. Once all three points have been placed, they may be individually selected and dragged to new positions.
→ Hold the Ctrl key while dragging the common point to toggle calculation of the reflex angle. Alternatively, double-click the common point.
→ Hold the Ctrl key while dragging the end points to snap it to the horizontal or vertical axis.
Measure custom lengths 
Click and drag the two points to measure the distance between them.
→ Hold the Ctrl key while dragging either point to snap it to the horizontal or vertical axis.
Length is measured at a scale determined by the body part of the selected metric, or from the centre of mass if no body part is selected.
Note: Custom length or distance measurements are limited to the vertical (top-to-bottom) and horizontal (side-to-side) axes. Measurements along the forward-backward axis are not currently supported.
Tips for accurate measurement
Do:
- Measure distances between body parts that are the same depth relative to the camera.
- Ensure the individual is directly facing the camera as much as possible when taking the snapshot.
- Confirm that you have selected the correct limb or side – this sets the z-value for scaling.
Don't:
- Measure distances between two points at different depths e.g. one closer to the camera and one further away. The system will over or underestimate the true distance.
- Move, tilt or rotate the camera between tests.
- Measure from the floor to a body point, unless you're certain the depth from camera is consistent.
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