In the same way that it is possible to map the sphere of our planet on two dimensions to produce a planisphere, we can map the sphere of the visual world. The first step is to project all the elements of the scene on the interior of a sphere (the center of the sphere is the camara lens). Then this sphere is mapped in two dimensions to create the Visual Planisphere
This image shows the product of mapping the sphere of a given space. N is the nadir and Z the zenith.