3D Stereo Data for the
Estimation of Pavement Construction
Quantities and Costs
Mr. Donald L. Reid
Department of Public Works
Nashville Metropolitan Government
GIS-T
March 27, 2007
Existing Process
• Numerous issues with
existing pavement data
• Accurate data collection
entails a manual, costly, and
time consuming process
• Alternative method could be
to use stereogrammetric
feature collection based on
stereo imagery
What is Stereo Imagery
• When you look at an object
you see it from different
angles with each eye
• Your brain merges these
images into a single image
to provide you with depth
perception…the ability to
perceive distance
• This enables you in essence
to see in “3D”
What is Stereo Imagery (cont.)
• When aerial imagery is collected it is collected such
that each picture overlaps the previous one by 60%
• This overlap provides an area in the two images of the
same place from different angles
• Through a process called aero triangulation it is
possible to accurately determine the exact x,y
position of each pixel in the image
• The images can then be mathematically aligned along
the flight line using a process called epi-polar
correction to enable a stereo view
• This enables viewing and measurement in 3D
Stereo Overlap
Shot 1
Flight
Path
Stereo Overlap
Shot 2
Stereo Overlap
Shot 1
Flight
Path
Shot 2
Stereo Overlap
Shot 1
Flight
Path
Stereo Overlap
Area
Shot 2
Example of Stereo
Overlap Area
Two Ways to See
Imagery in Stereo
• In order to see in stereo, we must trick our brain to
see stereo images in a way similar to that which we
normally use
• One way to trick the brain is to use a concept called
anaglyph
– Anaglyph uses one blue sensitive image and one red
sensitive image
– Using red-blue glasses we trick the brain to see two
images at once and let the brain do its’ magic
Anaglyph stereo image of
downtown Nashville
Stereo Viewing Using
Shuttered Glasses
• Electronically shuttered
glasses alternate putting one
image in the left eye and the
other image in the right eye
• If done at a image refresh
rate the brain processes the
images just as it would if it
were viewing in real life
• Desktop photogrammetric
work stations usually use
this method
• This the method being used
in our pilot program
Stereo Imagery Database
• Properly registered stereo imagery is accurate to to
+/- 1pixel in the horizontal axis and 1.5 pixel in the
vertical axis
– The Nashville data set is accurate to +/- 6” in
horizontal and +/- 9” in vertical
• Typical extracted feature accuracies are similar to
image accuracy depending on operator and training
• Accuracy is generally uniform throughout the image
– Digital orthoimagery accuracy is subject to accuracy
of imagery used to create the ortho
Imagery Access
• Individual stereo image pairs can be accessed using
any georeferenced data layer
• For Nashville Metro we are currently using a map
layer as the access layer
• Nashville/Davidson County is 112GB and contains
approximately 1400 stereo pairs
Stereo Imagery Provides
Feature Extraction Source
Desktop stereo photogrammetry provides:
• Improved accuracy over digital orthophotography
• Ability to measure distance over the ground
• Ability to extract 3D planimetric features such as
roof elevation footprints
• Ability to extract digital elevation (DEM’s and
topographic contours) for specific areas
Nashville Project Status
• Stereo imagery data has been prepared and project
access files prepared
• Hardware and software are installed and working
properly
• Training has been completed
• Pavement data collection process has been defined
• Data collection commenced this week
Questions/Contacts
Mr. Don Reid, Project Manager, Nashville Metropolitan
Government/Public Works
1-615-880-1673, [email protected]
Mr. Jeff Deason, GIS Management, Collier Engineering
1-615- 331-1441, [email protected]
Mr. Lonnie Hearne, Stereo Software, SimWright Inc.
1-615-497-0569, [email protected]