Photogrammetry
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Quantitative Measurements from Aerial
Photography
Flightlines of Vertical Aerial Photography
Stereoscopic Vision and Stereoscopes
Photo Alignment for 3D Visualization
Orthophotographs and DEMs
Reminder: Read Chapter 7 (pp. 193-218) for next
class
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http://www.dailymotion.com/video/xc4ixx_weather
man-freaking-out-over-dc-sno_shortfilms
What Quantitative Measurements can be obtained
from a Single Vertical Aerial Photograph?
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Scale
Object length
Area of photography or feature
Perimeter of feature
What Quantitative Measurements can be obtained
using Overlapping Stereoscopic Aerial Photographs
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Precise planimetric locations
Precise object height
Planimetrically accurate orthophotographs
Digital Elevation Models (DEMs)
Slope and aspect derived from DEMs
Flightline of Vertical Aerial Photography
Flightline of Aerial Photography
Direction of Flight
Exposure station
#1
#2
#3
lens
altitude
above
ground
level, H
60% overlap
stereoscopic model
Coverage of photograph
terrain recorded on three
successive photographs
Jensen, 2000
Block of Vertical Aerial Photography
Block of Aerial Photography
Flightline #1
oblique ph otography may be
acquired at th e end of a
flig htlin e as the aircraft
banks to turn
Flightline #2
20 – 30%
sidelap
Flightline #3
Jensen, 2000
Block of Vertical Aerial
Photography Compiled
into an Uncontrolled
Photomosaic
Columbia, SC
Original scale = 1:6,000
Focal length = 6” (152.82 mm)
March 30, 1993
Jensen, 2000
Flightline #4
Photo #5
Columbia, SC
Original scale = 1:6,000
Focal length = 6” (152.82 mm)
March 30, 1993
Jensen, 2000
Line of flight
Geometry of
Overlapping Vertical
Aerial Photographs
Photo 2
y - axis
Photo 1
Fiducial
mark
x-axis
• Principal Points
Principal
Point of
Photo #2
PP
Principal
Point of
Photo #1
PP1
2
a.
b.
Photo 2
Photo 1
• Conjugate Principle Points
PP1
CPP2
PP2
CPP1
line of flight
Principal Point of
Pho to #1 equals
Conjugate Principal
Point of Photo #2
c.
Prin cip al Poin t of
Pho to #2 equals
Conjugate Principal
Point of Photo #1
60% overlap
stereoscopic model
Jensen, 2000
Geometry of A Vertical
Aerial Photograph
Obtained Over
Flat Terrain
Geometry of A Vertical Aerial Photograph
Collected Over Flat Terrain
Jensen, 2000
Enlargement of A Portion of
Flightline #4, Photo #5
Jensen, 2000
Geometry of A Vertical
Aerial Photograph
Collected Over Variable
Relief Terrain
Jensen, 2000
Measurement of Object Height From A Single
Aerial Photograph Based on Relief Displacement
Jensen, 2000
Measurement of Object Height From A Single Aerial
Photograph Based on Shadow Length on Level Terrain
Meas urement of the Height of
Objects Bas ed on Shadow Length
tan a =
=
oppos ite
Su
n's
ra y
adjacent
height, h
s hadow, L
s
h
a
h = L x tan a
s hadow
L
Jensen, 2000
Stereoscopic Vision
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What is stereoscopic vision and what is its
significance for remote sensing?
Stereoscopic Vision
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3-D effect occurs when an object is viewed from two
different, but overlapping, viewpoints
Human eyes – up to ~1,000 m
Aerial photography – two successive aerial photos
with at least 60% forward overlap will provide
stereoscopic aerial photography
Basis for 3-D effect
0.119”
59.1’
Parallactic Angles Used
During Depth Perception
Jensen, 2000
Stereoscopic
Viewing
Methods
Jensen, 2000
Stereoscopes
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Deflect our normally converging lines of sight so
each eye views a different image
Lens (pocket) stereoscope
Reflecting stereoscope
Zoom stereoscope
Stereoplotters
Photo Alignment
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Identify principal point of each photograph
Locate conjugate principal point (or point(s) that
corresponds to principal point on adjacent photos)
Align points with flight line (straight line)
Line of flight
Geometry of
Overlapping Vertical
Aerial Photographs
Photo 2
y - axis
Photo 1
Fiducial
mark
x-axis
• Principal Points
Principal
Point of
Photo #2
PP
Principal
Point of
Photo #1
PP1
2
a.
b.
Photo 2
Photo 1
• Conjugate Principle Points
PP1
CPP2
PP2
CPP1
line of flight
Principal Point of
Pho to #1 equals
Conjugate Principal
Point of Photo #2
c.
Prin cip al Poin t of
Pho to #2 equals
Conjugate Principal
Point of Photo #1
60% overlap
stereoscopic model
Jensen, 2000
Lens Stereoscope with Parallax Bar
Jensen, 2000
Stereoscopic Parallax Principles
Jensen, 2000