When working with the HoloLens flavor of mixed reality, the very element that makes it mixed reality is that the holograms understand where your walls, ceiling, and floor are. They can, if coded to do so, even distinguish between a chair and a table. They can hide behind walls or in other rooms. They can even physically react to surfaces in simulated ways, that appear authentic.

This illusion is created primarily with Spatial Mapping, a mesh representation of your surroundings. This is the main reason that your HoloLens has all those sensors. So, to say we are in the heart of the process would be a fair assessment.

Occlusion is what allows holograms to be hidden. The purpose of occlusion is to tell the HoloLens, based on the spatial map, when to draw a hologram and when it is hidden or occluded from view.

As we will see in this chapter, the spatial map also simplifies object placement, using the various surfaces as a point of reference.