u42-TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS

# u42-TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS - UNIT...

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Sheet1 Page 1 UNIT 42 - TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS <toc.html#UNIT42> UNIT 42 - TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS Compiled with assistance from John H. Ganter, University of Pennsylvania * A. INTRODUCTION <#SEC42.1> * B. VERTICAL DIMENSION ("3D") <#SEC42.2> o Uses of 3D representations <#SEC42.2.1> * C. CHARACTER OF THE PHENOMENON <#SEC42.3> o Distribution <#SEC42.3.1> o Topological complexity <#SEC42.3.2> o Geometric complexity <#SEC42.3.3> * D. METHODS OF REPRESENTATION <#SEC42.4> o 2 1/2 dimensions <#SEC42.4.1> o True three dimensional representations <#SEC42.4.2> o Summary <#SEC42.4.3> * E. TIME DEPENDENCE <#SEC42.5> o Possible models <#SEC42.5.1> o Summary <#SEC42.5.2> * REFERENCES <#SEC42.6> * DISCUSSION AND EXAM QUESTIONS <#SEC42.7> * NOTES <#SEC42.8> UNIT 42 - TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS Compiled with assistance from John H. Ganter, University of Pennsylvania A. INTRODUCTION <#OUT42.1> * although the vast majority of GISs currently work only in two dimensions, across the plane, certain applications require the addition of other dimensions, namely time or elevation/depth o most geological applications require a consideration of attributes in the vertical dimension as well as the horizontal ones o temporal variations are important in many economic and social studies o oceanographic and meteorological models need to consider variations both in the vertical and the temporal dimensions * this unit will look briefly at how these additional dimensions can

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Sheet1 Page 2 be incorporated into GISs B. VERTICAL DIMENSION ("3D") <#OUT42.2> * there are two very different ways of looking at representations of the vertical dimension (normally called the third dimension) in GIS * the most commonly recognized is a data structure where a z value (normally elevation) is recorded as an attribute for each data point (x,y) o these z values can be used in a perspective plot to create the appearance of 3 dimensions o this is not true three dimensional representation and is often referred to as "2 1/2 dimensions" overhead - Perspective plot - Tiefort Mountains, CA, same data used for graphics in Unit 11 * these 2 1/2D plots are an attractive way of displaying topography and other continuous surfaces from DEMs or TINs o perspective plots can be computed from any viewpoint o additional layers can be "draped" over the surface using color o "artist's impressions" can be created by converting classes (e.g. of land cover) to simulated trees, etc. o with powerful computers, it is possible to animate 2 1/2D plots to create simulations of flying over topography + "LA the Movie" was created by Jet Propulsion Lab, Pasadena CA, by draping a Landsat scene over a DEM of LA, then simulating the view from a moving aircraft * true three dimensional representations store data in structures that reference locations in 3D space (x,y,z) o here z is not an attribute but an element of the location of the point o this permits data to be recorded at several points with
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## This note was uploaded on 10/05/2010 for the course GEO 591 taught by Professor Davidm.mark during the Fall '10 term at SUNY Buffalo.

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u42-TEMPORAL AND THREE-DIMENSIONAL REPRESENTATIONS - UNIT...

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