Normalizing the Normal Map

Abstract

Before becoming a cartographer, I made 3D graphics and animations. My favorite projects were those where I had to achieve my goals by using the tools available to me in ways that were very different from their intended purpose. As a cartographer, I’ve continued borrowing and “misusing” tools from computer graphics, especially the normal map. The more I use normal maps in cartography, the more I feel that they should be considered a common tool in both cartographic representation and GIS analyses. Unfortunately, up until recently there has been little mention of them in cartographic communities or scientific literature. I’d like to help popularize their misuse. Readers may already be familiar with the aspect-slope map (Figure 1), which represents surface orientation using two angular measurements. A normal map is the linear coordinate version of an aspect-slope map; it represents surface orientation using a type of 3D vector called a surface normal.