Lecture 17 Terrain modelling: applications

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Lecture 17Terrain modelling applications

• Outline
• introduction
• access modelling
• landscape evaluation

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Introduction

• Many applications of terrain models
• visualisation covered already
• hillshading and orthographic views
• animation and photorealism
• others
• access modelling
• visibility analysis and landscape evaluation
• slope and hazard mapping
• hydrological modelling

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Access modelling

• Terrain is a vital element for realistic access
  models
• flat, boundless plains of Weberian industrial
  location analysis just dont exist!
• need to take terrain-based costs into account
• Slope as push/pull factor
• Barrier features
• additional layer in GIS access models

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Distance models

• Isotropic distance models
• dont take cost factors into account
• e.g. eucdistance in GRID or buffer in Arc/Info
• Anisotropic distance models
• take cost factors into account
• e.g. costdistance in GRID

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Example distance model output
Buffer zones
Distance surface
Anisotropic surface
Residuals
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Routing models

• Cost or friction surfaces can be used to
  calculate shortest path between two points
• Euclidean model takes only distance into account
• result is straight line or as the crow flies
• anisotropic model takes cost or friction surface
  into account
• may be positive (push) or negative (pull)
• uses cost of traversing a cell in a particular
  direction to identify least accumulative cost
  route
• result is unlikely to be a straight line

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Example routing output
Crianlarich-Benmore circular walk
Minimum distance/time surface
Check-points
Actual route
Predicted route
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Case study modelling remoteness

• Off-road accessibility is function of
• distance from nearest road
• slope relative to direction of travel
• ground conditions (trafficability)
• barrier features (rivers, lakes, cliffs, etc.)
• Combine within anisotropic access model as cost
  or friction surfaces

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Question

• What other cost factors might we include in a
  model of off-road accessibility?

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Remoteness model

• Combined model integrating
• Dijkstras Shortest Path Algorithm
• calculate shortest path from origin to any
  destination based on relative costs of movement
  through set of cells between origin and
  destination
• Naismiths Rule (1892)
• an hour for every three miles on the map, with
  an additional hour for every 2,000 feet of
  ascent
• -10 minutes/300 m descent for slopes 5gt12 10
  minutes/300 m descent for slopes gt12

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Results

• Naismith's/Dijkstra's model used to model
  relative remoteness of Cairngorms area under
  different scenarios
• with and without mountain-bike access along
  trails
• before and after proposed ski funicular
• ArcGIS alternative Costpath
• calculates the least-accumulative-cost distance
  over cost surface from source cell(s) accounting
  for surface distance and horizontal/vertical cost
  factors.

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What if? modelling of Mountain bike
restrictions Mar Lodge estate
With mountain bike use along track from Linn of
Dee
Without mountain bike use along track from Linn
of Dee
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Effects of the Cairngorm Ski Funicular
With parking restrictions at the Day Lodge and
along access road
Without parking restrictions at the Day Lodge or
along access road
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Visibility analysis

• Use of DTM to calculate viewshed of particular
  point
• where can point X be seen from on surface Y?
• what part of surface Y can be seen from point X?
• Multiple point viewsheds combined to calculate
  viewshed of line and area features
• where and part of feature X be seen on surface Y?
• what part of surface Y can be seen from which
  point on feature X?

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Calculating viewsheds

• Uses line of sight from observer point to terrain
  surface to calculate intervisibility matrix
• visible parts of terrain surface
• non-visible areas (i.e. dead areas)
• Use of observation point and terrain offsets
• e.g. height of person or observation tower
• e.g. height of wind turbine or other feature

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Calculating an inter-visibility matrix
Offset a
Offset b
v
v
v
nv
nv
nv
without offset b
with offset b
not visible
visible
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Example viewsheds
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Uses of visibility analysis

• Many different uses
• visual impact analysis
• landscape evaluation
• siting of observation towers and cellular
  communications masts
• modelling coverage of cellular communications
• military applications
• virtual GIS

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Wind farm impact assessment
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Landscape evaluation of Scotland
Intervisibility matrix (After Miller)
50m DEM
Littons 1968 scenic assessment
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Landscape evaluation of Britain
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Visual impact of human features
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Cell phone coverage
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Military applications
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Virtual GIS
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Conclusions

• Many uses for DEMs in environmental applications
  of GIS
• key variable determining accessibility
• important landscape variable
• controlling factor in gravity hazards including
  flooding, avalanches, landslides, etc.

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Practical

• Visibility assessment
• Task Calculate viewshed of a wind farm
• Data The following datasets are provided
• Digital elevation model (50m resolution 150,000
  OS Panorama data)
• Wind farm turbine location(s)
• ITE LCM90 data

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Practical

• Steps
• Display DEM and turbine locations in ArcMap or
  GRID
• Calculate viewshed of wind turbines using both 1
  and 16 turbines assuming a turbine height of 30m
  using visibility
• Display results in ArcMap or GRID

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Learning outcomes

• Familiarity with the VISIBILITY command in
  Arc/Info
• Experience with developing impact assessments
  based on environmental variables

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Useful web links

• Access modelling
• http//www.geogr.ku.dk/dkgs/image/pub_pdf/artikler
  /2002/GT2002_05tb.pdf
• Archaeology and viewshed analysis
• http//www.casa.arizona.edu/MPP/viewshed/vspaper.h
  tml
• Scenic highway designation
• http//crssa.rutgers.edu/projects/highway/highway.
  html

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Next week

• Hydrological modelling
• Basics of hydrology
• Creating hydrologically correct DEMs
• Modelling catchment variables
• Practical
• Derive stream network from DEM