The instructor is using a 3D object, such as a solid cube, to demonstrate how it can be viewed from different angles. When the cube is viewed parallel to the x,y plane, such as from directly above, the cube appears to be a 2-dimensional square. The same can said when viewed from the front and from the side, the cube's appearance is a 2D square. When the cube is viewed from an angle, such as the angle known as SW, you see the top, side and front all at the same time.
The ability to see three surfaces of the cube at the same time is an axonometrical view. The axonometrical views from a 3D cube are only possible when the cube is rotated around one or more of its axes to reveal more than one side.
Can you get axonometrical views from an object drawn in 3D? Yes, of course. Can you get axonometrical views from an object drawn in 2D? Yes, you still can.
By drawing lines at appropriate angles, you can create a 2D drawing that appears to be a cube. This 2D representation of a cube is considered an axonometrical 'drawing.' Why? Because the drawing, which uses angled lines, is displaying more than one side.
Print a 2D isometric drawing of cube, then print a 3D isometric view of the exact same cube, lay the printed sheets on a desk and, in theory, you won't be able to tell them apart.
To efficiently deal with axonometric views, AutoCAD uses tools such as UCS, named views, and the magic tool you allude to, the Viewcube. (Enter Viewcube on command line to see the magic.)
Back in the day, prior to the invention of AutoCAD, this was the way to draw 3D, using angled lines in a 2D drawing environment. Today, AutoCAD has enhanced 3D creation through technology. Whether isometric, dimetric or trimetric, the instructor is simply demonstrating how viewcube technology applies to axonometricals.
Chicagolooper
