High Accuracy Photogrammetric Mapping from Large Scale Aerial Photography

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High Accuracy Photogrammetric Mapping from Large
Scale Aerial Photography
Ron BergDeputy Chief Surveyor Ministry of
Transportation Geomatics Office October, 2004
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Outline

• MTO photogrammetric mapping background
• Bancroft pilot project
• Highway 417 implementation project
• Current projects
• Conclusions

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Accuracy Standards

• Based on the Scale of Photography
• Horizontal - 30 microns at photo scale
• for 13000 photography 69 cm
• for 11000 photography 63 cm
• for 1600 photography 6 2 cm
• Vertical - 30 microns (hard surfaces) and 75
  microns (soft surfaces) at photo scale
• for 13000 photography 69 cm and 623 cm
• for 11000 photography 63 cm and 68 cm
• for 1600 photography 6 2 cm and 6 5 cm

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Helicopter Methodology

• Aerial photography by helicopter allows
• Lower flying height (90m 150m)
• Larger photo scale (1600 11000)
• Higher accuracy (2cm - 8 cm)

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Photography Coverage
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13000 vs. 1600 photography
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MTO Objectives

• The objectives of using helicopter methods were
  to
• determine if ground survey accuracy could be
  achieved from the air
• get surveyors off the asphalt
• reduce or eliminate lane closures

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Bancroft Project
Highway 62
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Bell Jet Ranger 206B
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90 metre flying height
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Photogrammetric Mapping

• 5 - 10 times enlargement (zoom) is reasonable
  when viewing photography for photogrammetric
  mapping
• 1600 becomes 1120 at 5 times zoom
• The Vertical component is also exaggerated to aid
  measurement

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1600 Results

• Aerial triangulation showed maximum residuals
  less than 2 centimetres
• Control points set every 50 metres
• Coordinated by conventional levelling, total
  station and GPS.

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1600 Results

• Consultants were able to clearly define
• top of curb and edge of gutter
• gutter somewhat difficult due to poor contrast on
  concrete
• gas and water valves, overhead wire crossings
• wheel ruts and pavement variations
• They felt comfortable reading vertical
  differences of 15 - 20 millimetres

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MTO Audit Data
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Centreline
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Hard Surfaces
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Ground
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Potential Benefits

• Achieve ground survey accuracy from aerial
  methods
• Greatly reduce ground activity on travelled lanes
• increase safety for workers
• reduce traffic disruption
• Collect more information for less cost than
  ground survey

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Drawbacks

• Requires extensive ground control before
  photography is flown
• however most points can be set off travelled
  highway lanes
• More costly than 13000 mapping

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Implementation

• Implement the technology on a major highway where
  benefits can be realized
• 30 km of Highway 417 (Ottawa Queensway)
• The project was delayed due to restrictions on
  flying height over built up areas with a single
  engine helicopter.

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Flying Options

• Transport Canada gave us two options
• fly at 90 m with a single engine helicopter and
  full lane closures (i.e. shut down the highway
  NOT AN OPTION) or,
• fly at 150 m with a twin engine helicopter and no
  lane closures.

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Option 2

• We chose the second option, flying at 150m with a
  twin engine helicopter
• This would sacrifice 1-2 cm in accuracy but
  maintain our other objectives
• Get surveyors off the highway
• Minimize lane closures

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Development

• An Ontario firm has developed an aerial camera
  mount for a twin-engine helicopter which was
  approved by Transport Canada in March, 2003
• 30 km of Highway 417 through Ottawa was flown by
  helicopter at 11000 scale in May 2003

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Hwy 417Hwy 416 to Anderson Road
Start
End
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AT Results

• RMS VALUES OF RESIDUALS OF PHOTOGRAMMETRIC
  OBSERVATIONS
• image system terrain system
• image points
• obs x 17985 rms x 8.95 rms x
  0.009
• obs y 17985 rms y 11.29 rms y
  0.012
• RMS VALUES OF RESIDUALS OF NON-PHOTOGRAMMETRIC
  OBSERVATIONS
• image system terrain system
• control points
• obs x 477 rms x 10.96 rms x
  0.011
• obs y 477 rms y 11.29 rms
  y 0.012
• obs z 486 rms z 14.47 rms
  z 0.015

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AT Vertical Residuals
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Were Objectives Met?

• Accuracy
• MTO collected ground surveyed audit data
  throughout project.
• Comparisons are generally better than 4 cm on
  hard surfaces, 10 cm on soft surfaces.

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Were Objectives Met?

• Get surveyors off the asphalt
• Absolutely!
• Surveyors worked within the highway corridor to
  place control, but they accomplished this off
  traveled lanes.

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Were Objectives Met?

• Reduce or eliminate lane closures
• Lane closures were not required for the project.
  
• To survey this stretch using traditional
  methods would require months of lane closures.

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Were Objectives Met?

• Cost
• Substantially cheaper than traditional methods on
  this particular project.
• For MTO projects, this approach is less costly
  than traditional ground surveys that require
  extensive traffic control.

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Current Projects

• Highway 401 Kingston
• Highway 400/401 Interchange
• Highway 427/409 Interchange

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Highway 401 Kingston
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Highway 400/401
Highway 401
Highway 400
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Highway 427 Toronto
Pearson Airport
Highway 427
Highway 409
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Highway 401
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Conclusions

• Two MTO projects have been successfully
  completed. Three projects are in progress.
• The helicopter methodology can support pavement
  data collection accurate to 2 - 4 centimetres.
• This methodology is ideal for inaccessible areas,
  dangerous or high traffic volume areas and where
  extensive traffic control would be required to
  conduct ground surveys.

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Municipal Applications?

• High traffic volume roads
• Bridges
• Water treatment plants, hydro plants
• Dangerous or environmentally sensitive areas
• ???

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Consider Imagery
Aerial imagery and mapping should be considered
for many municipal applications

• Satellite
• Large projects
• Economical if in-stock
• Low resolution (1-100m)

• Aerial photography
• Small or large projects
• Ideal for corridors
• High to medium resolution (5 - 50 cm)

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Safer Surveying

• Other investigated technologies that improve
  worker safety
• Reflectorless total station
• Terrestrial laser
• Airborne lidar
• Airborne GPS photogrammetry
• ARAN vehicle (mobile video mapping)

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• MTOs Geomatics Office has conducted studies to
  examine the potential of using large scale aerial
  photography taken by low-flying helicopter to
  provide a high-accuracy photogrammetric mapping
  product suitable for detailed engineering design.
  Results from two projects indicate that high
  accuracy pavement data collection can be achieved
  without sending surveyors onto the travelled
  lanes, reducing field crew exposure to heavy
  traffic, thereby providing a safer, more
  efficient way of collecting the critical pavement
  data. Using this technology reduces the need for
  expensive and inconvenient traffic protection
  measures such as lane closures and use of blocker
  trucks, reducing traffic congestion and traffic
  control costs.