CARTOGRAPHICAL DATA TREATMENT ANALYSIS FOR REAL TIME THREE-DIMENSIONAL TERRAIN VISUALIZATION Flávio Luis de Mello & Luiz Felipe Coutinho Ferreira da Silva Divisão de Tecnologia da Informação - DTI & Seção de Engenharia Cartográfica - SE6 Centro Tecnológico do Exército - CTEx & Instituto Militar de Engenharia - IME

1 Summary 1. Introduction 2. Real Time Systems 3. The Terrain Mesh 4. The Cone Vision 5. The Triangulation Construction Study Case 6. Results 7. Conclusion

Introduction Alternative solution for the triangulation problem of altimetric data of cartographic features Main goal: allow data management obtain real time 3D terrain visualization from 2D topographic charts Application is supposed to be executed on low performance computers embedded on military tanks, vehicles and soldiers combat equipment The methodology is constrained by this obsolete hardware (upper bound: Pentium 300 MHz) 2

3 Real Time Systems Application metric: scene refresh rate Execution Time industrial and electrical plants, intensive therapy units elastic time response maritime traffic control, cosmic probes navigation snapshot response definition is not associated to the elapsed time, but to an opportune problem treatment Real time animation: over 12 fps

4 The Terrain Mesh Impossible to know exactly the heights of all points on a surface Attribute the same height to all neighboring points near a sample height Each point is connected using straight line segments in order to compose a triangle set, and each triangle vertex is raised until its corresponding height Each triangle vertex corresponds to a point measure on the object surface

4 The Terrain Mesh Impossible to know exactly the heights of all points on a surface Attribute the same height to all neighboring points near a sample height Each point is connected using straight line segments in order to compose a triangle set, and each triangle vertex is raised until its corresponding height Each triangle vertex corresponds to a point measure on the object surface Delaunay triangulation

5 The Cone Vision Scene vision composed by several layers Complex scenes If it is possible to determine the invisible geometries before being drawn, it would be possible simply to ignore them, thus preventing the unnecessary data processing

6 Spatial Indexing

7 The Triangulation Construction Study Case Piraquara Extract (MI SE), 1:25,000 2,478 points

8 The Triangulation Construction Study Case 2,478 points 5,173 triangles Piraquara Extract (MI SE), 1:25,000

8 The Triangulation Construction Study Case 2,478 points 5,173 triangles Piraquara Extract (MI SE), 1:25,000

9 Results The time spent by the graphical device to draw the scene over the monitor screen is inversely influenced by the quantity of geometrical primitives Frustum culling algorithm Douglas-Peucker generalization contributes for reducing the number of geometries necessary for the exhibition Altimetry data represents about 76% of all the map data (average)

10 Results points triangles Piraquara (MI SE), 1:25,000 Test = 1 GHz 233 MHz GeForce2 64MB PCI GeForce2 64MB AGP S3Virge 1MB PCI 1x1, 2x2, 4x4, 8x8, 16x16, 32x32, 64x64, 128x128

11 Results

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13 Conclusion It was possible to improve the application performance to higher values than the lower limits defined by classic animation literature The results analysis suggests that it is possible to create a real time 3D terrain visualization application based on the current available cartographic data and obsolete hardware Future work includes: remaining data layers, cartographic symbology, texture rendering, database transaction.

14 Questions _________ ____ ____________ ___ ________ ____ ______ ____________ _____ __________ ________ ____ _____