How to Get 2D Drawings Out of 3D Models

How to get two-dimensional drawings to look like three-dimensional objects is a basic problem of drawing. A series of marks on a flat two-dimensional surface must create the illusion of reality where things have height, width and length. Rendering the volumes and planes of objects on a flat surface to fool the eye into thinking they're real has preoccupied draftsmen and artists since the days of cave painting. The discovery, or rediscovery, of the rules of linear perspective during the Renaissance was a major breakthrough in the development of illusionistic drawing. The geometry of objects in space and how they appear to the human eye were codified into a set of rules by Leon Battista Alberti in his 1435 book "On Painting."

Instructions

1. Set up the three-dimensional models you are going to render in two dimensions. Organize them into a tastefully arranged still life. Illuminate your models with natural sunlight or a strong source of artificial light. Have the light hit the objects from the right, left, or from above. Use a simple, uncluttered background for your drawing. Tape the drawing paper to your drawing board.

2. Observe the three-dimensional models closely to perceive their geometrical structure. See the basic shapes that make up more complex forms. Look very closely at the objects, your level of drawing is determined by your level of observation. See how the light falls on the models and casts shadows to define the volume of the shapes.
  
3. Use linear perspective to foreshorten your objects so they appear to recede into space. Draw simple compositions with one-point perspective using a single vanishing point on the horizon. Employ the technique of two-point perspective for more complicated drawings. Make all the lines of your objects converge on double vanishing points. Use consistent vanishing point trajectories for a consistent illusion of depth. Keep your lines even by using a straight edge tool.
  
4. Represent the pictorial effects of illumination on your models. Study the shadows closely. Use your darkest values for the umbra shadows on the edges of objects that are farthest from the light source. Draw the penumbra, or the secondary illuminated shadow that forms the midtone values. Use the contrast between light and dark to achieve a chiaroscuro, or volumetric affect.
  
5. Render shadows by blending adjacent tones with a paper stump or kneaded eraser for a smooth look. Draw with hatched strokes (short parallel lines) to suggest your forms and break up their outlines. Use cross-hatching to indicate shadowed areas. Angle the cross-hatched lines to follow the curvature and contours of your models. Use thicker lines in shadowed areas. Add your highlighted accents with an eraser to finish the drawing.
For more info- http://www.ehow.com/how_7852490_2d-drawings-out-3d-models.html