The External Positonal Device Tracker (EPDT) feature is part of the Vuforia Engine Driver Framework. The EPDT defines all the specifics required for Vuforia Engine to access external pose data.
Prior to the introduction of this feature, Vuforia Engine internally handled pose data acquisition. With EPDT, developers can define how Vuforia Engine acquires pose data. The EPDT must implement several APIs which Vuforia Engine uses to access the external system. For more information on how to create your own EPDT, refer to Creating a Custom Driver.
Vuforia Driver does not currently support Ground Plane. Additionally, EPDT results in ModelTargets operating less robustly. Vuforia Engine also provides a File Driver sample which demonstrates how to access image and pose data from external systems.