The Alexandria Digital Earth Prototype Michael F. Goodchild University of California Santa Barbara

Outline n The grid n Digital Earth –geolibraries

Grid issues n Primitive elements –quadrilaterals –triangles –hexagons n Fast rendering n Hierarchical nesting n Consistency –no interruptions, major distortions

More issues n Uniformity –topology –area –shape n Identification –unique –single string –sequential –explicit resolution

The Platonic solids n Tetrahedron n Cube –quadrilaterals n Octahedron –triangles n Dodecahedron n Icosahedron –triangles

Discrete global grid based on the Icosahedron (20 triangles, 1:4 recursive subdivision) Ross Heikes and David Randall, Colorado State University

Digital Earth n An instance of massive integrated representations –Digital Galaxy –Digital Human –Digital Los Angeles n Possibly distributed –transparent to the user

Perspectives on Digital Earth n 1. An immersive environment –“I believe we need a 'Digital Earth'. A multi- resolution, three-dimensional representation of the planet, into which we can embed vast quantities of geo-referenced data.” U.S. Vice President Gore, 1/98 n Spin, zoom, pan –"fly-by" technology

Immersive environments n Head-mounted devices n Immersadesk n The "cave" n Standard computer displays –2D window on manipulable 3D objects –Nick Faust, Georgia Tech –SRI Digital Earth, Terravision –powerful processors, 3D graphics

Perspectives on Digital Earth n 2. A metaphor for organizing information n The geolibrary –a library that is searchable by geographic location –"what have you got about there?" –physically impossible but feasible in a digital world

NRC report n "Distributed Geolibraries: Spatial Information Resources"

Perspectives on Digital Earth n 3. A collection of knowledge about the Earth's dynamics –the processes that create and modify the landscape n Dynamics or statics? –most GIS data are cross-sectional time- slices < providing facts –understanding of the Earth must focus on processes

A dynamic Digital Earth n Simulations of past and future conditions n A library of simulation models –applied to local conditions represented by data n A tool with enormous educational value