Stereographic Projection in Spherical Coordinates

The stereographic projection of two antipodal points: \documentclass[ tikz ,border = 3.14mm ]{standalone} \usepackage{tikz-3dplot} \usetikzlibrary{ arrows.meta ,angles } \pgfmathdeclarefunction{sphereX}{2}{% % #1 - longitude % #1 - latitude \pgfmathparse{cos(#2) * cos(#1)}% } \pgfmathdeclarefunction{sphereY}{2}{% \pgfmathparse{cos(#2) * sin(#1)}% } \pgfmathdeclarefunction{sphereZ}{2}{%…