Used by permission. An example of the lines an illustrator would use to convey the shape of this airplane foot pedal. Changing which isolines are displayed can change the perception of the surface. The image on the right looks as if it has a deeper pit because the isolines go thru the maximum curvature point on the surface. Images courtesy of David Johnson.
Illustrators use lines to separate parts of objects and define important shape characteristics.
This photograph of a metal object shows the anisotropic reflections and the white edge highlights which illustrators sometimes depict. Illustrators combine edge lines with a specific type of shading. Shading in technical illustration brings out subtle shape attributes and provides information about material properties. For the Mesh Method, there are up to four dot products that need to be calculated per mesh point, only one per mesh point for Srf-Node Method. View of surface with silhouettes generated with mesh method.