Setting up Vanishing Points Tutorial

Something that came up in the midst of Pencil King's Perspective Challenge - there's lots of resources out there on how to draw boxes and so forth but the basic setup of a perspective picture is a bit more mysterious.  In order to avoid distortion - usually, things looking "squished" because the vanishing points are too close together - you MUST put them fairly far apart. But HOW far apart?? This method solves that problem by working backwards to establish the cone of vision and from there find the station point and the minimum distance for the vanishing points.