Fig 4. Schematic for tangent and angle computation.

The black curved line represents the junction and the black arrows tagged by ${\widehat{\mathbf{n}}}_{\mathbf{i}}$, ${\widehat{\mathbf{n}}}_{\mathbf{j}}$, and ${\widehat{\mathbf{n}}}_{\mathbf{k}}$ represent the normal vector of each membrane face. The red vector $\widehat{\mathbf{m}}$ is an approximation to the junction’s tangent vector. The blue plane represents the perpendicular plane to the red vector $\widehat{\mathbf{m}}$. The blue vectors are the projected normals, which lie in the plane normal to $\widehat{\mathbf{m}}$, and thus are coplanar. On the right, we demonstrate that the angle of intersections can be calculated from the tangent vectors ${\widehat{\mathbf{t}}}_{\mathbf{i}}$, ${\widehat{\mathbf{t}}}_{\mathbf{j}}$, and ${\widehat{\mathbf{t}}}_{\mathbf{k}}$ from each membrane normal to the junction.