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Spatial & Terrain Analysis

in 3D. Spatial & Terrain Analysis. Nigel Trodd Coventry University. Aim & objectives. To understand the application of 2D+ terrain analysis in GIS. to review methods of 2D spatial analysis to identify 1st and 2nd order derivatives of DEM data

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Spatial & Terrain Analysis

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  1. in 3D Spatial & Terrain Analysis Nigel Trodd Coventry University

  2. Aim & objectives • To understand the application of 2D+ terrain analysis in GIS • to review methods of 2D spatial analysis • to identify 1st and 2nd order derivatives of DEM data • to identify advanced methods of terrain analysis 3D … improves communication & interaction … is essential for environmental modelling … drives new methods of data capture & management

  3. we should not rush these things without some basic spatialdatamodelling

  4. dimensionality Entitation points, lines, areas volumes surfaces • 2D • 3D • 2.5D Data modelling geometry topology spatial concept not a problem 2D + above, below DEM, TIN, voxel

  5. Measurement of inherent properties • simple geometric measurements associated with objects Point – none! Line - length, mid-point Area - perimeter, area, centroid, shape Surface – mean, min, max, range, variance Volume – volume, centroid

  6. Spatial analysis in 2D

  7. Definition of spatial analysis • A method of analysis is spatial if the results depend on the locations of the objects being analyzed e.g. • move the objects and the results change Or • the analysis modifies geometry or creates new geometry

  8. Spatial operators Berry, J.K., 1987, Fundamental operations in computer-assisted map analysis, International Journal of GIS1 119-36. • Reclassifying maps • Overlaying maps • Proximity and connectivity • Characterizing neighbourhoods

  9. Reclassify • Change or create a new entity using spatial properties Reclassify & then merge adjacent areas with the same attribute i.e. change geometry

  10. Overlay analysis • Point in Polygon • Polygon on Polygon

  11. Polygon on Polygon overlay for raster data

  12. Proximity analysis: buffering • Create a new area within a user-defined distance of an existing entity e.g., to determine areas impacted by a proposed highway

  13. Contiguity analysis Which states share a border with Missouri?

  14. Neighbourhood analysis • Local operators calculate an output value based on the values of nearby locations • Zonal operators • Focal operators • the area(s) of interest is defined by another data layer • the area of interest is defined by a user-specified moving window

  15. Focal operators output at a location calculated from the values at locations in a window

  16. Terrain analysis DEM visualisations DTM 1st order derivative 2nd order derivative in 2.5D

  17. 1st order derivatives

  18. 2nd order derivatives

  19. Terrain analysis watershed

  20. Terrain analysis viewshed

  21. Summary & Conclusion • 3D GIS is appealing - but rarely implemented • 2.5D is frequently implemented using a surface entity type • Terrain analysis in 2.5D exploits multiple visualisations of a DEM and its’ 1st and 2nd order derivatives • 2.5D products make useful inputs to environmental models • Much (most?) terrain analysis still relies on spatial operations in 2D

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