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

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