The quick sketch technique

Above about the quick sketch technique.

When drawing, a basic understanding of the rules of perspective is essential if you are to achieve a realistic effect. Only once you have learned these rules you can begin to distort or exaggerate them in order to accentuate elements of your design. There are three basic forms of perspective (one, two and three point). There are also three main elements present in each of these (the vanishing point, convergence lines and horizon line). This tutorial shows the basics behind one and two point perspective only, three-point perspective being a technique that automotive sketching does not require.
Horizon Line: This line, as its name suggests, describes the horizon, which is always considered to be at eye level. For instance, an object sited above the horizon line is above the viewer's eye level and will therefore show its underside.
Vanishing Points: Sited on the horizon line these are the points where all convergence lines meet. Although always on the horizon, their position on the horizon depends on the viewer's angle to the viewed object.
Convergence Lines: All parallel lines in a scene will always appear to converge to a single point (the vanishing points). The exception to this rule is that lines viewed in parallel or perpendicular to the viewer will not converge. In one and two point perspective you can also consider all vertical lines as non-converging lines.
One Point Perspective: One point perspective is evident when the object being viewed lies parallel or perpendicular to the viewer. This means that only lines travelling towards or away from the viewer appear to converge to a single vanishing point on the horizon. Picture one shows how this makes for a very simple version of perspective, which is especially useful for sketching quick side views of a vehicle.
Two Point Perspective: When the object being viewed lies at an angle to the viewer, as in the second sketch example, all the horizontal lines appear to converge. This therefore introduces a second vanishing point on the horizon. Where the vanishing points fall on the horizon line depends on the angle of the object to the viewer. Looking at picture two you can see that if the vehicle were turned so that more of the side was visible, then the right vanishing point would move to the right and out of the image.
Wheel Ellipses: Getting correct ellipses when drawing a car is probably the hardest part of perspective. Getting it absolutely correct will probably not add anything to your drawing, but getting it wrong however will make your drawing look very odd. If you look at a circle at an angle of 90 degrees then what you see is indeed a circle. Once you start to reduce the angle you view the circle from, it starts to appear to be an ellipse. An ellipse has a Major Axis and a Minor Axis. In picture three you can see where these are situated on an ellipse. The Major Axis divides the ellipse into two equal halves along the longest dimension, whilst the Minor Axis divides the ellipse into two equal halves along its shortest dimension. Although not technically complete (the full explanation is long, more complicated and not generally required when sketching) a good rule of thumb is that you should always align the Minor Axis with the axle of your vehicle. The Major Axis, and therefore the longest dimension of the ellipses should therefore run perpendicular to your axle line. Finally, how do you ensure that the angle of your ellipse is correct? There is a method using construction boxes, but in practice you should not need this for sketching. If you ensure that you have got all of the above correct then the angle, or width of your ellipse hopefully should be self-evident.