Spatial & Terrain Analysis

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# Spatial & Terrain Analysis - PowerPoint PPT Presentation

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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Presentation Transcript

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

spatialdatamodelling

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

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

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 GIS1 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
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
• 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 operators

output at a location calculated from the values at locations in a window

Terrain analysis

DEM visualisations

DTM

1st order derivative

2nd order derivative

in 2.5D

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