In mathematics, real projective space, denoted R P n {\displaystyle \mathbb {RP} ^{n}} or P n ( R ) , {\displaystyle \mathbb {P} _{n}(\mathbb {R} ),} is the topological space of lines passing through the origin 0 in the real space R n + 1 . {\displaystyle \mathbb {R} ^{n+1}.} It is a compact, smooth manifold of dimension n, and is a special case G r ( 1 , R n + 1 ) {\displaystyle \mathbf {Gr} (1,\mathbb {R} ^{n+1})} of a Grassmannian space.