A designer needs the ability to sketch out and explore design intentions through the development of basic volumetric forms. A sketch exploration can be developed quickly and manipulated instantly, and is essential for forming a clear concept for the development of a design to follow. In the early stages this representation can take the form of an isometric or simple one-point perspective sketch. You will often find it useful to sketch out your proposals before attempting to model a scheme in CAD.
A simple axonometric/perspective sketch that analytically explores an object in three dimensions.
A 3D sketch model created out of scrap ...