Overview of the different coordinates in use and the transformations between them. Bottom centre is a schematic representation of a void in real space in the true cosmology. The overall shape of the void is spherical, as expected from statistical isotropy. In the top panel (red), we apply a redshift-space distortion, which elongates the void along the line of sight. The right-hand side shows what happens when the wrong cosmology is assumed in the analysis, while the left-hand side shows voids from a simulation used to obtain templates, which are spherically symmetric but whose sizes may vary in simulations with different cosmologies.