It's Not What You Draw,It's What You Don't Draw

Abstract

The R graphics engine has new support for drawing complex paths via the functions polypath() and grid.path(). This article explains what is meant by a complex path and demonstrates the usefulness of complex paths in drawing non-trivial shapes, logos, customised data symbols, and maps. One of the design goals of the R graphics system (R Development Core Team, 2011) is to allow fine control over the small details of plots. One way that the R graphics system does this is by providing access to low-level generic graphics facilities, such as the ability to draw basic shapes and the ability to control apparently esoteric, but still useful, features of those shapes, such as the line end style used for drawing lines. In R version 2.12.0, another low-level graphics facility was added to R: the ability to draw complex paths (not just polygons). This article describes this new facility and presents some examples that show how complex paths might be useful. Drawing paths with holes The concept of a path is similar to the concept of a polygon: a path is defined by a series of (x,y) locations that describe the boundary of the path. For example, the following code defines a set of (x,y) locations that describe a simple triangle. > x y <c(.1, .8, .1) A triangle can be drawn from these locations using either the polypath() function from the graphics package or, as shown below and in Figure 1, using the grid.path() function from the grid package.