Topological properties of the so-called "plane at infinity". When 3D-Euclidean geometry is extended with ideal points at infinity, a whole "plane at infinity" is added to the geometry.
Apart from metric properties it has become a 3D projective space and 
the plane at infinity is a regular projective plane.   
On the other hand we experience infinity as a "sphere" around us at infinite distance.
I mean in the real world.
Does anybody have suggestions on how to bring the view of a plane and a sphere together, looking at topological properties of the "plane at infinity"?
Put in other words: what kind of topological model for the "plane at infinity" would be appropiate?

Think of a family of all lines passing through a point in $\mathbb{R}^3$. Now start moving this point to infinity. In the limit the family turns into a family of parallel lines. By definition, the plane at infinity is the set of these families, it's a projective plane, not an ordinary Euclidean plane. 
Different families have different directions so it seems that we can use the sphere to represent them. However, antipodal directions produce the same family of parallel lines, so we would have to identify antipodal points on the sphere to represent the plane at infinity faithfully. And that's a standard way to describe the projective plane. Many topological properties of the projective plane can be established by using this construction of it as a quotient of the sphere.
