Visual Analysis

1
Visual Analysis

• Determination of line of sight
• Viewshed mapping
• Visual impact modelling
• References
• Fisher, P.F. (1996) Extending the applicability
  of viewsheds in landscape planning,
  Photogrammetric Engineering and Remote Sensing,
  62297-302.
• Hadrian, D.R., Bishop I.D. and Mitcheltree, R.
  (1988) Automated mapping of visual impacts in
  utility corridors, Landscape and Urban Planning,
  16261-282.
• Bishop, I.D. (in press) Determination of
  thresholds of visual impact the case of wind
  turbines. Environment and Planning B Planning
  and Design

2
Line of sight

3
Visual Profile
4
Viewshed Parameters
5
Visibility Map

• Effect of screening
• Dealing with curvature
• Binary output
• Missing horizons
• Effect of DTM errors?
• see Fisher

6
Screening
7
Partial Screening
8
Curvature effects
d
(Rh)2 R2 d2 R2 2Rh h2 R2 d2 2Rh
d2 h d2 / 2R R radius of earth d distance
on surface h correction , difference between
actual Z and assumed Z
h
R
2
R
9
Earths Curvature
The formula used for the correction is Zactual
Zsurface - (DISTANCE2 / DIAMETEREarth) 0.13
(DISTANCE2 / DIAMETEREarth) where DISTANCE is
the planimetric distance between the observation
point and the observed point. The third term
accounts for the refraction of visible light.
The value used for the diameter of the Earth is
12,740,000 meters.
10
Visibility of tall objects

• h 0.87 d2 /D
• d sqrt(14.64h)
• h in m, d in km
• assuming observer and object at same elevation
  and flat surface between

11
Additional issues.

• Binary output
• Missing horizons
• Effect of DTM errors?

12
Composite Visual Assessment

• Multiple relevant view points
• visual features
• visual intrusions
• ground coverage

13
Visibility
14
Visual Prominence
15
Visual Models
16
Impact Modelling Factors

• Visual components
• Thresholds (size and contrast)
• Impact - Distance relationships
• Visual absorption
• Site sensitivities
• Observer sensitivities (activity dependent)

17
Thresholds
Bishop, I.D. (in press) Determination of
thresholds of visual impact the case of wind
turbines. Environment and Planning B Planning
and Design Shang, H.-D., and Bishop, I. D.
(2000) Visual thresholds for detection,
recognition and visual impact in landscape
settings Journal of Environmental Psychology 20,
125-140.
18
Quality Modelling Factors

• Visual quality contributors
• Distance zoning
• Model structures
• image based or map based
• location based or view based
• regression, neural net
• Need for public input
• http//www.geom.unimelb.edu.au/cgism/idb_papers/N
  N/Neural_net.html

19
Web based surveys
http//www.arbld.unimelb.edu.au/hbit/ http//www.
sli.unimelb.edu.au/survey/LSP97