Perspective drawing, as like technical or instrumental drawing is governed by guidelines. Once you are able to understand and apply the rules, perspective drawing becomes easier to master. These rules are applicable to both Plan Projection and Direct Projection.
All parallel planes converge into their respective Vanishing Lines (VL) at visual infinity
The figure above shows how the planes that construct a 3-Dimensional form Width and Height, Depth and Height and Width and Depth, all converge into their respective vanishing lines at visual infinity.
The vanishing points for all rectangle forms will converge into the intersections of the Horizontal Vanishing Line and the Vertical Vanishing Line for the plane in which it lies.
All Parallel Lines converge into Vanishing Points (VP) on the Vanishing Line (VL) for the plane they represent.
Perhaps one of the most misunderstood aspects to perspective drawing is that this third guideline. Essentially, it means that perspective drawings can have more Vanishing Points (VP) than just the those where the vertical and horizontal planes intersect, that is, a one point perspective drawing can have more than one vanishing point and likewise, two point perspective drawings can have more than two vanishing points.
It should be assumed that each drawing plane can contain an infinite number of converging lines. These additional vanishing points exist when each set of converging lines require Vanishing Points (VP) on the Vanishing Lines they are located on. This guideline must be understood in order for the Vanishing Points (VP) of angular or diagonal features are located. This includes features such as the angular pitch of a roof, shadow casting and placing objects at angular views.