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GIS _ Terrain Analysis

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					                           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
• to identify advanced methods of terrain
  analysis                                            3D
                   … improves communication & interaction
                  … is essential for environmental modelling
       … drives new methods of data capture & management
    we should not
    rush these
    things
  without some basic

spatial data
 modelling
         dimensionality
                    Entitation
• 2D       points, lines, areas
• 3D       volumes
• 2.5D     surfaces


        Data modelling
  geometry          not a problem
  topology          2D + above, below
  spatial concept   DEM, TIN, voxel
   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
Spatial analysis
                   in
                   2D
  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
           Spatial operators
    Berry, J.K., 1987, Fundamental operations in computer-
  assisted map analysis, International Journal of GIS 1 119-
                                                         36.

• Reclassifying maps
• Overlaying maps
• Proximity and connectivity
• Characterizing neighbourhoods
                        Reclassify
  • Change or create a new entity using
     spatial properties




Reclassify & then merge adjacent areas
with the same attribute i.e. change
geometry
         Overlay analysis
• Point in Polygon
• Polygon on Polygon
Polygon on Polygon overlay
for raster data
    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
      Contiguity analysis




Which states share a border with Missouri?
     Neighbourhood analysis
• Local operators calculate an output value
  based on the values of nearby locations

• Zonal operators
    – the area(s) of interest is defined by another data
      layer
• Focal operators
    – the area of interest is defined by a user-specified
      moving window
Focal operators
output at a location calculated
from the values at locations in
a window
               in
Terrain analysis
               2.5D
        DEM visualisations
        DTM
          1st order derivative
          2nd order derivative
1st order derivatives
2nd order derivatives
Terrain analysis




      watersh
      ed
Terrain analysis




viewshe
d
       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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posted:2/13/2012
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