Gnomonic projection
= Gnomonic projection
{title2=$(\xi,\eta)$}
{wiki}
The gnomonic projection intersects rays from a <sphere>’s centre with a tangent plane. If $\mathbf b$ is its unit normal and $\mathbf e,\mathbf n$ are tangent basis vectors, a direction $\mathbf s$ maps to $f(\mathbf s\cdot\mathbf e,\mathbf s\cdot\mathbf n)/(\mathbf s\cdot\mathbf b)$. It maps <great circle> arcs to straight lines and is singular at the tangent-plane horizon.