Overview

The Leap Motion Controller tracks hands and fingers and reports position, velocity, and orientation with low latency and good accuracy. The controller can be used on a tabletop or mounted on a VR headset.

The Leap Motion controller system consists of a hardware device and a software component which runs as a service or daemon on the host computer. The software component analyses images produced by the hardware and sends tracking information to applications. The Leap motion Unreal plugin connects to this service and translates the tracking data into the Unreal coordinate system.

Coordinate Systems

The Unreal Engine uses a left-handed convention for its coordinate system, wheras the Leap Motion API uses a right-handed convention. Unreal also uses a default unit of centimeters, wheras the Leap Motion API uses millimeters. The plugin automatically transforms the tracking data to use the left-handed coordinate system and scales distance values to centimeters.

https://di4564baj7skl.cloudfront.net/documentation/v2/images/unreal/Unreal_Axes.png

The Unreal left-handed coordinate system superimposed on the Leap Motion device in its desktop orientation.

When you place a LeapMotionControllerActor object in a scene the 3D hands created by the plugin are aligned to the local coordinate system of that object.

When you turn on HMD mode in the plugin, the plugin rotates the 3D hands to maintain the proper orientation to the Unreal world.

https://di4564baj7skl.cloudfront.net/documentation/v2/images/unreal/HMD_Unreal_Axes.png

The Unreal coordinate system in relationship to the Leap Motion device in HMD mode.

Hand Tracking

The Leap Motion controller uses optical sensors and infrared light. The sensors have a field of view of about 150 degrees. The effective range of the Leap Motion Controller extends from approximately 3 to 60 centimeters above the device (1 inch to 2 feet).

https://di4564baj7skl.cloudfront.net/documentation/v2/images/Leap_View.jpg

The Leap Motion controller’s view of your hands in desktop mode

Detection and tracking work best when the controller has a clear, high-contrast view of an object’s silhouette. The Leap Motion software combines its sensor data with an internal model of the human hand to help cope with challenging tracking conditions.

https://di4564baj7skl.cloudfront.net/documentation/v2/images/VR-distance.png

Particularly in HMD mode, you should ensure that there is less distance between the sensor and your hands then between your hands and any background objects or walls.