# GIS _ Terrain Analysis by hcj

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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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