Don't be confused with orthographic projection
orthographic are perspective projection are ways to transform 3d scene into a 2d surface.
Definition
Given an n-dimensional vector space
and a p-dimensional subspace of , and being an orthonormal basis for . Let be a vector in , the orthogonal projection of onto is given by
When we are doing orthogonal projection, we throw away the part of the vector that are not part of the subspace. Say if