Visibility Surfaces

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Visibility Surfaces
Line-of-Sight Technical Working Group 23
September 2003 Doug Caldwell Topographic
Engineering Center
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Outline

• Complete Intervisibility Database Concept
• Computing Architecture
• Visibility Surface Metrics and Tactical Decision
  Aids

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Current Visibility Products
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Complete Intervisibility Database
Generate a Masked Area Plot of Every Point in
a DEM. Idea originated with Clark Raye and Bob
Richbourg (USMA) in early 1990s. They derived
products from the analysis, but did not retain
the masked area plots.
Multipoint-to-Multipoint
Point-to-Point Line-of-Sight
Point-to-Multipoint Masked Area Plot
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The Computational Challenge
Southwest Harbor, Maine USGS Digital Elevation
Model 336 Rows x 466 Columns 156,576 Masked Area
Plots
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A Multi-Computing Solution
http//www.cs.wisc.edu/condor/

• Utilizes wasted computer cycles on remote
  computers
• Does not require changes to existing code
• Runs on Windows or UNIX
• Previously solved problem requiring 10.9 years
• of CPU time in 7 days

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The Computing Architecture
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Cumulative Visibility
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
Visibility for Masked Area Plot at Each Grid
Point. May Be Measured as Count Area Percent
Total Area
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Slope of Cumulative Visibility
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
Slope of Cumulative Visibility for Masked Area
Plot at Each Grid Point. May Be Measured
as Degrees 0o 90o Percent 0 - Infinity
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Other Metrics
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
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Percent Target Visible
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
Percent of Target Feature Visible From Any
Location Measured as Percent 0 - 100
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Lack of Symmetry in Visibility
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
Occurs when observer and target height not equal
Target
Observer
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Least/Most Visible Route
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.
Least/Most Visible Route Cumulative visibility
used as a cost surface.
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Summary
Fragmentation (8-Connected)
Fragmentation records, for each point in the DEM,
the total number of connected regions contained
within the viewshed for each observer location at
that point. The lower value of this measure can
equal one, with higher values indicating
locations with greater masked area plot
fragmentation. Fragmentation is largely
controlled by the nature of the intervening
features. Fragmentation provides an indication of
the degree of connectedness of the viewsheds.

• Visibility surfaces provide insights into
  intervisibility characteristics of the terrain
  that are not available from line-of-sight or
  masked area plots.
• Calculation of visibility surfaces is
  computationally intensive and requires
  significant storage
• High Throughput Computing solutions, like Condor,
  address the computing issues.
• Creation and exploitation of visibility surfaces
  is an open research area.

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Visibility Surfaces

• Douglas R. Caldwell
• US Army Topographic Engineering Center
• 7701 Telegraph Road
• Alexandria, VA 22315
• Phone[phone] X2236
• Email Douglas.R.Caldwell_at_erdc.usace.army.mil