In tracker-less AR the user decide that where he/she wants to place the virtual object. How it works, is that the camera maps the real world into and augmented space and allows the customer to place digital content in the space and interact with it.
For that, depth-sensing cameras were introduced to add the perception of depth in cameras for better environment recognition and detection.
Then the customer can drop digital content on the ground and view it in their real-time environment. Tracker-less is used for those applications which do not require an “anchor” to the real world. It means that virtual/augmented objects will appear to “float” in mid-air. But there are also the possiblities to automatically place a 3D AR object onto a flat surface which increase realism, for instance placing a bag onto a table.