Automating Landscape Illustration with Pen and Ink Style Rendering

This paper introduces object space procedures for extracting silhouettes, slope lines, and drainage features from digital elevation models (DEMs) to direct the rendering of landform features in the style of pen-and-ink landscape illustrations. Unlike image space procedures which generally extract feature information through 2-dimensional (2D) rendered image processing techniques, object space procedures operate directly on 3-dimensional (3D) surface models. The ultimate goal of this work is to produce fully automated tools that can imitate the styles characterized by the traditional pen-andink techniques of Lobeck, Imhof, Raisz, and other scientific illustrators to bring the beauty of their effective and economical visual techniques to automated cartographic environments. Through the implementation of a Java 3D application programming interface (API) prototype, a testing platform was established for the application of stylistic elements to linework representing surface form lines. This paper explores the aesthetic effects of silhouette lines, creases, and slope lines on the rendering of terrain features. It also introduces the use of adaptively resampled triangulated irregular networks (TINs) as a basis for perspective rendering applications. Cartography and Geographic Information Science, Vol. 36, No. 1, 2009, pp. 117-128 Introduction The art of perspective landscape illustration has a long history in the study and description of landforms and their underlying geological structures. Imhof (2007, pp. 1-14) traced its development from Mesopotamian relief representations through Renaissance copper engravings and on to modern illustrations derived from topographic map construction. Flemer (1895) provided an exhaustive treatment of the theory and photographic technology supporting ground-based, perspective imaging of landforms. His work specifies methods for capturing panoramic images based on numerous individual photographs with known fields of view, and for constructing topographic maps from the panoramas. Raisz, himself one of the foremost practitioners of block and landform diagram construction, attributed the modern introduction and perfection of this form to the work of Grove Karl Gilbert and William Morris Davis (Raisz 1948, p. 301-308). Armin Lobeck, whose Block Diagrams has remained one of the most influential guides to their manual construction, argued that these penand-ink illustrations gain much of their effectiveness from their visual simplicity (Lobeck 1958, p. 1). This research explores the application of Lobeck’s aesthetic to the automatic construction of perspective landscape illustrations from digital elevation models (DEMs) under the rubric of non-photorealistic rendering. It reviews earlier work on automated systems, introduces a new testing platform for stylistic experimentation, presents the relevant underlying algorithms for the production of the major visual elements, and discusses the contributions of these elements to good expression of landscape form. Previous Related Work Over the past decade, the rapid development cycle of fast, relatively inexpensive graphics processing chips, along with concomitant developments in 3D application programming interfaces (APIs), has fostered a period of intense growth in perspective rendering applications in cartography, GIS, and in non-geographic disciplines. Much of this work has been related to realistic renderings of landscapes, whether for gaming, site planning, or other uses that require a relatively “complete” description of a scene. Kennelly and Kimerling (2006) noted that another rendering paradigm, non-photorealistic rendering (NPR), provides a close analogy to the construction of traditional landscape line drawings by fostering the communication of specific, often scientific information through a language composed of symbols with well understood meanings. The goals of NPR are consistent with those of cartographic forms that use the rules and conJames E. Mower, University at Albany, Department of Geography and Planning, AS 218, University at Albany, Albany, New York 12222 USA. E-mail: . Tel: 518-442-4779; Fax: 518-442-4742.