Spatial & Terrain Analysis Nigel Trodd Coventry University in in 3D 3D
Jan 03, 2016
Spatial & Terrain Analysis
Nigel Trodd
Coventry University
in in 3D3D
Aim & objectives
•To understand the application of 2D+ terrain analysis in GIS
… improves communication & interaction
… is essential for environmental modelling
… drives new methods of data capture & management
33DD
• to review methods of 2D spatial analysis• to identify 1st and 2nd order derivatives
of DEM data• to identify advanced methods of terrain
analysis
we should not we should not rush these rush these thingsthings
without some basic
spatialspatial datadata modellingmodelling
dimensionality
• 2D• 3D• 2.5D
Entitationpoints, lines, areasvolumessurfaces
not a problem2D + above, belowDEM, TIN, voxel
Data modellinggeometrytopologyspatial concept
Measurement of inherent properties
• simple geometric measurements associated with objects
Point – none!Line - length, mid-pointArea - perimeter, area, centroid, shapeSurface – mean, min, max, range,
varianceVolume – volume, centroid
Spatial analysisin 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
changeOr– 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 entitye.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
• 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
Focal operatorsoutput at a location calculated from the values at locations in a window
Terrain analysisin 2.5DDEM visualisations
DTM1st order derivative
2nd order derivative
1st order derivatives
2nd order derivatives
Terrain analysis
watershed
viewshed
Terrain analysis
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