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GEOM30009: Imaging the Environment
Measuring 3D in images:
introduction to photogrammetry (and Lidar)
Kourosh Khoshelham
Measuring 3D in images
2
Topics
• Stereo viewing in overlapping images
• Concept of parallax
• Tools for measuring 3D in images
• Close range photogrammetry
• LiDAR
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Stereo viewing in overlapping images
Stereo (3D) viewingOverlapping photographs
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Acquisition of overlapping aerial images
Typically
60%~80%
overlap and
20%~30%
sidelap.
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Photogrammetric flight planning
Source: www.aibotix.com
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Concept of parallax
▪ Parallax is the relative
movement of objects in
overlapping images due to their
different distances from the
camera.
▪ Parallax in the direction of flight
line (x-parallax) is the basis for
measuring height in overlapping
images.
Parallax from a car window!
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Measuring parallax
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Tools for stereo viewing and 3D measurement
• (Digital) stereoplotters are
used for 3D measurement in
images and map production.
• Stereoplotters have tools for
3D viewing and digitization of
features.
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Tools for stereo viewing and 3D measurement
Types of stereo viewing systems:
• Anaglyphic
• Split-screen
• Active shuttering eyewear
• Active modulating panel
• Dual monitor
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The Power of Love (1922) was the first 3D feature film.
Source: thevintagenews.com
Anaglyphic Stereoscopic viewing
• The left image is displayed using
red color palette and the right image
is displayed using blue and/or green
color palette;
• Anaglyph glasses have a red filter
and a blue-green filter allowing the
left eye to see the left image and
the right eye to see the right image,
resulting in a stereoscopic (3D)
view;
• Simple and low cost but restricted
colour and problematic
superimposition.
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• The monitor is split into two
halves: the left image is
displayed in the left half and
the right image in the right
half;
• With the use of a stereoscope
mounted in front of the
monitor a stereoscopic model
can be viewed;
• Simple and cheap, but
restricted 3D viewing area;
only one viewer.
Split screen stereoscopic viewing
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• Consists of a monitor that displays the
two images alternately, an infra red (or
radio frequency) emitter and an eyewear
that can shut the view of each eye.
• The infra red emitter synchronizes the
eyewear shutters with the graphic
hardware of the display: when the left
image is displayed the view of the right
eye is shut, and when the right image is
displayed the view of the left eye is shut.
• Requires a 120+Hz monitor;
• Heavy eyewear, but good colour, 3D
effect and superimposition;
Shuttering
glasses
Infrared synchronizer
Active shuttering eyewear
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Active modulating panel (ZScreen)
• Consists of a monitor that displays
the two images alternately, a
polarization panel placed in front of
the monitor and polarized glasses;
• The polarization of the panel changes
at a rate synchronized with the
graphics processor that alternates
right and left image displays on the
screen of the monitor;
• Requires a 120+Hz monitor;
• Good color viewing, 3D effect and
superimposition; light-weight glasses.
modulating panel Polarized glasses
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• Consists of two LCD displays, a beam-
splitter mirror, and a pair of crossed
polarizing glasses;
• When the image from the upper display
is reflected off the mirror its polarization
changes by 90 degrees, whereas the
polarization of the lower image remains
unchanged;
• Using the polarized glasses the user
sees the left image with the left eye and
the right image with the right eye;
• Good colour and 3D effect, but bulky
and expensive, needs adjustment.
Crossed-
polarizing
glasses
Dual monitor
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Close range photogrammetry
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Close range photogrammetry
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Example 1: 3D reconstruction of the Royal Exhibition Building
Close range photogrammetry
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Example 2: 3D reconstruction of the teeth
Lidar
• LiDAR: Light Detection And Ranging
• Aka: laser scanning, laser ranging, laser altimetry
• State-of-the-art technology for 3D measurement and mapping of natural
and built environments
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Handheld &
Wearable
• Indoor mapping
• Utility mapping
• Asset tracking
• …
Different lidar platforms
Airborne*
• Terrain mapping
• 3D city modelling
• Vegetation analysis
• …
Terrestrial
• As-built BIM
• Heritage modelling
• Deformation
monitoring
• …
Mobile
• Mapping road
environments
• Autonomous
vehicles
• …
* Including drones. Spaceborne lidar also exists but does not include a scanner.
Lidar measurement principle
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Emitted
laser pulse
Returned
laser pulse
1) Lidar measures
distance based on time
of flight of the laser
pulse. It also records the
scan angle.
2) It reconstructs the
position vector using
the orientation of the
sensor measured by an
inertial measurement
unit (IMU).
3) It computes the 3D
position of the point
using the position of the
sensor measured by
GNSS.
Emitted
laser pulse
Returned
laser pulse
Roll
Pitch Yaw
Emitted
laser pulse
Returned
laser pulse
Example application: 3D terrain modelling
• Coastal zone management
– coastal erosion
– dune monitoring
• Water management
– water level decisions
– water board taxes
– flood (risk) assessment
• Insurance
• Avalanche risk assessment
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Example application: 3D city modelling
• urban planning
• real estate tax
• real estate agents
• telecommunications planning
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Example application: Corridor mapping
• roads
• railroads
• power lines
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Example application: archaeological mapping
• Archaeological
landscape structures