This article explains how to use an arbitrary scale in your virtual Unity scene despite Vuforia Engine requiring all targets to be configured accurately in meter scale.
Vuforia Engine requires the size of all targets to be defined in meters. It is important that the size is configured as accurately as possible since it is used to compute the pose of the target – its position and orientation in space.
Vuforia Fusion unites tracking information from the camera feed and the device sensors. If the size of a target is not configured correctly, poses computed from the camera image and the sensors do not match, which will cause various tracking issues.
Starting with Vuforia 9.0, there is a simple mechanism to transform all Vuforia Targets into whatever virtual scene scale you are using. It is called Virtual Scene Scale Factor and can be found in the Vuforia Configuration.
Setting the Physical Scale of a Model Target
The physical size of a target is set in the dataset, but can also be configured in the Unity inspector for a particular target: