Aerial photogrammetry chapter pptx-1.pdf

Haramaya University
CSSH
School of GeES
Department of Geo−Information Science
Aerial Photography and Photogrammetry (GISc3085)
By Kassaye Hussien (Ass. Professor)
June ,2021
1

Arial Photography and
Photogrammetry
Lessons
1. Photogrammetry
2. Principal design of aerial cameras
3. Internal camera geometry
4. Types of aerial photographs
5. Vertical aerial photographs
6. Stereo pair photographs
7. Photographic scale
8. Relief displacement
9. Image parallax
10. Air photo interpretation
11. Orthophoto
2
BY KASSAYE HUSSIEN

Objectives:
• Up on completion of the chapter you will be able to:
 Define photogrammetry,
Describe historical background of Aerial photography and
photogrammetry
Explain types of photogrammetry
Understand photogrammetric products
 Describe principal design of aerial cameras,
 Classify aerial photographs,
 Understand stereo-pair photographs,
 Define photographic scale,
 Describe relief displacement,
 Define image parallax,
 Describe airphoto interpretation techniques.
3

 What is Photogrammetry?
 Definition
 There is no universally accepted definition of
photogrammetry. The definition given below captures the
most important notion of photogrammetry.
 Photogrammetry - measuring from photographs
 The name “photogrammetry" is derived from the three Greek words
 photos – ‘light’
 gramma -that which is ‘letter or drawn or written"
 metron -to ‘measure’
•
4
1.Introduction

Cont…
 Photogrammetry is the technique of measuring objects
(2D or 3D) from photographs.
 Its most important feature is the fact, that the
objects are measured without being touched
 Photogrammetry → metric exploitation of imagery
5

Definition……
•Photogrammetry: is defined as the art, science or
technology of obtaining reliable information about physical
objects and the environment through processes of:
 recording,
 measuring, and
 interpreting photographic images
 Remember this: Photogrammetry is the metric
interpretation of image data
 Photogrammetry is a measurement technology in which
the three dimensional coordinates of points on an object
is determined.
 This is achieved by stereoscopy, which is measurements
made in two (or more) photographic images taken from
different positions (different views).
6

Cont.
•The imagery can be acquired by
 special aerial photo cameras
 video cameras
 digital cameras
 radiation sensors
• The imagery could be stored as
 conventional photographs in paper form(hardcopy)
 digital images on tape or СD(soft copy)
 The output of photogrammetry is typically a map, drawing,
measurement, or a 3D model of some real-world object
or scene.
7

• Two distinct areas are included within this definition of
Photogrammetry:
i. Metric Photogrammetry: which consists of making precise
measurements from photos and other information sources to
determine the relative locations of points.
• This enables finding distances, angles, areas, elevations,
and the sizes and shapes of objects.
ii. Interpretive Photogrammetry: deals principally in
recognizing & identifying objects and judging their
significance through careful and systematic analysis from
photographic images.
• When we can identify what we see on the photographs and
communicate this information to others, we are practicing air
photo interpretation.
8

Cont…
 These images created from satellite imagery which senses
energy in wavelengths.
 Forms basis for remote sensing (art or science of gathering
information about an object or image without actually
coming into physical contact).
 Photo interpretation involves in the study of photographic
images, while remote sensing involves not only the analysis
of photography but also the use of data collected from
remote sensing instruments.
9

Cont…
 In order to simplify understanding an abstract definition
and to get a quick grasp at the complex field of
photogrammetry, look to systems approach (Table. 1.1).
10

Cont..
data acquisition photogrammetric
procedures
photogrammetric
products
photographic products
enlargements/reductions
rectifier rectifications
orthophoto projector orthophotos
camera --->
photographs
comparator points
Stereo plotter DEMs, profiles, surfaces
scanner
analytical plotter maps
topographic maps
sensor ---> digital
imagery
softcopy workstation special maps
11
Table 1.1: Photogrammetry portrayed as systems approach. The input is usually
referred to as data acquisition, the “black box" involves photogrammetric
procedures and instruments; the output comprises photogrammetric products.

Cont…
 The first stereoplotters (Kelsh Plotter) where projection
stereoplotters
◦ they used only the light rays and optics to adjust the image
 The next was the analog stereoplotters
◦ they used more sophisticated optics to view the image.
 The analytical stereoplotter is used today.
◦ It incorporates a computer which does the work of
mathematically aligning the images so that they line up
properly.
◦ allows for storing the data and redrawing at any desired
scale.
12

Cont…
 A rectifier is kind of a copy machine for making plane
rectifications.
 Orthophoto projector generates orthophotos
 A comparator is a precise measuring instrument which lets
you measure points on a diapositive (photo coordinates).
◦ It is mainly used in aerial triangulation.
◦ In order to measure 3-D positions of points in a stereo model, a
stereo plotting instrument or stereo plotter for short, is used.
 An analytical plotter establishes the transformation
computationally. Both types of plotters are mainly used to
produce maps, DEMs and profiles.
13

CONT..
15
A. Analytical Stereoplotter
B. Kelsh Projection Stereoplotter

Data Acquisition…
 How can we get Data in RS? OR
 Describe the process of data acquisition in RS.
 How can we get data in Photogrammetry? Or
 Describe the process of data acquisition in PGM.
16

Data acquisition
 Data acquisition in photogrammetry is concerned with
obtaining reliable information about the properties of surfaces and
objects without physical contact with the objects which is, in
essence, the most obvious difference to surveying.
 The remotely received information can be grouped into four
categories:
 Geometric information involves the spatial position and the
shape of objects. It is the most important information source in
photogrammetry.
 Physical information refers to properties of electromagnetic
radiation, e.g., radiant energy, wavelength, and polarization.
 Semantic information is related to the meaning of an image. It
is usually obtained by interpreting the recorded data.
17

Cont…
 Temporal information is related to the change of an object in
time, usually obtained by comparing several images which were
recorded at different times.
 As indicated in Table 1.2 the remotely sensed objects may range
from planets to portions of the earth’s surface, to industrial parts,
historical buildings or human bodies.

 The generic name for data acquisition devices is sensor,
consisting of an optical and detector system. The sensor is
mounted on a platform.
 The most typical sensors are cameras where photographic
material serves as detectors. They are mounted on airplanes as
the most common platforms.
 Table 1.2 summarizes the different objects and platforms and
associates them to different applications of photogrammetry.
18

Cont…
object sensor platform specialization
planet space vehicle Space Photogrammetry (d >30km)
earth’s surface airplane space vehicle Aerial Photogrammetry (2km -10km)
industrial part tripod Industrial Photogrammetry
historical building tripod Architectural photogrammetry
human body tripod Biostereometrics
19
Table 1.2
Close Range (d <10m) andTerrestrial PGM (10m -100m)
On the basis of platforms or camera location

Check Points
 What is photogrammetry (PGM)?
 Compare and contrast RS and PGM?
 Explain the differences between metric and interpretative
photogrammetry.
 Describe the types of PGM On the basis of orientation of
camera axis, sensor system used, principle of recreating
geometry, procedure involved for reducing the data from
photographs and Applications Point of View (Reading
Assignment).
 Discuss the importance of photogrammetry in geographic
information systems.
 List field of studies that intensively apply PGM.
20

Fundamental principle of Photogrammetry
 The fundamental principle used by photogrammetry is
triangulation.
 Triangulation is the principle used by both photogrammetry
and theodolites to produce 3-dimensional point
measurements.
 By taking photographs from at least two different locations,
so-called “lines of sight” can be developed from each camera
to points on the object.
 These lines of sight (sometimes called rays owing to their
optical nature) are mathematically intersected to produce
the 3-dimensional coordinates of the points of interest.
21

CONT…
 Aerial Triangulation (AT) in Photogrammetry is
methods of determine and calculate 3D object coordinates
by photogrammetric means, by using photographs exposed
from different positions, covering the same object.
◦ measure several unknown point clearly visible in
the aerial triangulation in a stereo instrument.
◦ the inputs for aerial triangulation
 Scanned Images
 Camera Report
 Ground Control Data/ Ground Control Point
22

Cont…
 AerialTriangulation is classified three categories:
◦ Analogue Aerial Triangulation
◦ Semi Analytical Aerial Triangulation
◦ Analytical Aerial Triangulation
◦ Digital Aerial Triangulation (automation)
23

Cont…
 Advantages AT
 Minimizing delays and hardships due to adverse weather
condition.
 Access to much of the property within the project area is
not required.
 Field surveying in difficult area, such as Marshes, Extreme
slope, volcanic areas, hazardous rock formation, etc; can be
minimized.
24

Cont…
 Triangulation is also the principle used by theodolites for 3D
coordinate measurement.
 If you are familiar with these instruments, you will find many
similarities (and some differences) between photogrammetry and
theodolites.
 Triangulation is also the way your two eyes work together to
gauge distance (called depth perception).
 Two eyes can measure relative distance to scene point,
using geometric triangulation
25

Check Points
 Explain triangulation.
 Describe advantages of AT.
 What are the inputs for AT
26

Assignment one (20%)
1.What is photogrammetry? (PGM) (1%)
2. Compare and contrast RS and PGM. (2%)
3. Explain the differences between metric and interpretative.
photogrammetry. (3%)
4. Describe the types of PGM On the basis of orientation of
camera axis, sensor system used, principle of recreating
geometry, procedure involved for reducing the data from
photographs and Applications Point ofView (5%).
5. Discuss the importance of photogrammetry in geographic
information systems. (5%)
6. List field of studies that intensively apply PGM. (1%)
7. Explain triangulation. (1%)
8. Describe advantages of AT. (1%)
9. What are the inputs for AT. (1%)
27

Photogrammetry versus Remote Sensing
 The principle difference between photogrammetry and remote
sensing is in the application;
 While photogrammetrists produce maps and precise three-
dimensional positions of points, remote sensing specialists
analyze and interpret images for deriving information about
the earth’s land and water areas.
 Photogrammetry is the science of measuring distances, angles,
areas, etc. in photographs. These measurements are then able to
be mathematically transferred into “real world” measurements.
 Given that these photogrammetrically derived real-world
measurements are gathered “remotely”, i.e. not “on the ground”
or “in the real world”, enables us to label it as “remote
sensing”.
 “Remote Sensing” on the other hand, can deal with all other
sensors (e.g. RADAR, SONAR, imaging, etc. and doesn’t
necessarily rely on spatial measurements as it’s main concern.
28

Cont…
 As depicted in Fig. 1.1 both disciplines are also related to
Geographic Information Systems (GIS)
◦ they provide GIS with essential information.
◦ Quite often, the core of topographic information is produced by
photogrammetrists in form of a digital map
29
Figure 1.1: Relationship of
photogrammetry, remote sensing and GIS.

1.2 Historical Background
 Origin of photogrammetry
 aerial photography was the base for the emergence of
Photogrammetry.
 The First photographs taken in 1839
 Balloons, Kites, Pigeons were used to capture Photo
from air( till aeroplane were invented)
30
The English meteorologist E. D.
Archibald was among the first to
take successful photographs from
kites in 1882
He used a string of kites, with the
camera being attached to the last
1882
1858

Historical Background
Historical development of Aerial photograph
31
The first aerial photography taken
from an airplane was in 1909, by
Wilbur Wright.
1909
The first successful aerial
photograph from a rocket mounted
camera was taken by the Swedish
inventor, Alfred Nobel in 1897
1903
In 1903 the Bavarian Pigeon Corps used
pigeons to transmit messages and take
aerial photos. Julius Neubronne patented
the "breast mounted pigeon camera". The
camera weighed 70 grams and took
automatic exposures every 30 seconds.
1897

Cont.…
 The first photo ever taken from space on October 24, 1946
from a cool 65 miles up (104.607km), it was taken with a
35mm camera mounted on a V-2 missile launched from the
White Sands Missile Range in New Mexico.
32

Historical Background…
Satellites, Since 1972 (high resolution)
33

Check Points
 Explain the historical development of PGM
34

Photogrammetry
Photograph vs. Image
35

Historical development of Photogrammetry
 The development of photogrammetry clearly
depends on the general development of science
and technology.
 It is interesting to note that the four major phases
of photogrammetry are directly related to the
technological inventions of
 photography,
 airplanes,
 computers and electronics.
36

Check Points
 Explain the difference between photograph and Image
 Explain the historical advancement of PGM.
 Describe the relationships among PGM, RS and GIS?
37

1.3 Phases of Photogrammetry
A. First generation - Plane table photogrammetry
B. The second generation (analog photogrammetry)
C. Third Generation(Analytical)
D. The fourth generation( digital photogrammetry)
38

Phases of Photogrammetry:
 Phases of Photogrammetry:
A. First generation - Plane table photogrammetry
 Measurements made on a map on a table.
 Photographs used to extract angles.
 Photogrammetry had its beginning with the invention of
photography by Daguerre and Niepce in 1839
 First use of terrestrial photographs for topographic maps -
Laussedat, 1849 ‘Father of photogrammetry". City map of
Paris (1851).
 Film - Eastman, 1884.
39

Phases of Photogrammetry
 Major photogrammetric phases as a result of technological
innovations.
40

Phases of Photogrammetry….
B. The second generation (analoge photogrammetry) is
characterized by the invention of stereo photogrammetry by
Pulfrich (1901).
 This paved the way for the construction of the first
stereoplotter by Orel, in 1908.
 World War One was a major impetus(a driving force) to
development of aerial photography
 Airplanes and cameras became operational during the first
world war.
 Between the two world wars, the main foundations of aerial
survey techniques were built and they stand until today.
41

Analogue Photogrammetry
 Optical or mechanical instruments were used to
reconstruct three-dimensional geometry from two
overlapping photographs.
 The main product during this phase was topographic
maps
42
Optical Mechanical

Photogrammetry
 Aeroplane (Wright 1903). First aerial imagery from
aeroplane in 1909.
 The Wright brothers, Orville (August 19, 1871 –
January 30, 1948) and Wilbur (April 16, 1867 – May
30, 1912), were two American brothers, inventors.
43

Phases of Photogrammetry…..
C.Third Generation:
 With the advent of the computer, the third generation has
begun, under the motto of analytical photogrammetry
 Schmid was one of the first photogrammetrists who had
access to a computer.
 He developed the basis of analytical photogrammetry in the
fifties, using matrix algebra.
 For the first time a serious attempt was made to employ
adjustment theory to photogrammetric measurements
 Apart from aerial triangulation, the analytical plotter
(Helava 1957) is another major invention of the third
generation
 Analytical plotter - image-map coordinate transformation
by electronic computation
44

Phase of photogrammetry…..
Analytical Photogrammetry :
 The computer replaces some expensive optical and
mechanical components.
 The resulting devices were analog/digital hybrids.
 Analytical aerotriangulation, analytical plotters, and
orthophoto projectors were the main developments
during this phase.
 Outputs of analytical photogrammetry can be
topographic maps, but can also be digital products,
such as digital maps and DEMs
45

D.The fourth generation( digital photogrammetry)
is rapidly emerging as a new discipline in photogrammetry.
 In contrast to all other phases, digital images are used
instead of aerial photographs.
 With the availability of storage devices which permit rapid
access to digital imagery, and special microprocessor
chips, digital photogrammetry began in earnest only a few
years ago.
 The field is still in its infancy and has not yet made its way
into the photogrammetric practice.
46

 Digital photogrammetry:
 is applied to digital images that are stored and
processed on a computer.
 Digital photogrammetry is sometimes called softcopy
photogrammetry.
 The output products are in digital form, such as
digital maps, DEMs, and digital orthophotos saved on
computer storage media.
47

cont
 Single or pairs of digital images are loaded into a
computer with image processing capabilities.
 Images may be from satellite or airborne scanners,
CCD cameras or are conventional photographs
captured by a line scanner.
 Images are either displayed on the screen for operator
interpretation, enhanced by image processing or
subjected to image correlation in order to form a
digital elevation model (DEM) or extract details.
48

cont
 The inventions of the following devices have been
contributing the development of Digital
photogrammetry:
 Charge-Coupled Device (CCD) (Boyle, Smith 1969).
 Landsat (1972)
 Digital camera (Sesson (Eastman Kodak) 1975 - 0.01
Mpixels).
 Flash memory (Masuoka (Toshiba) 1980).
49

Why photogrammetry
 Extracting geometrical information and producing
maps.
 Cheaper than terrestrial methods.
 Extracting qualitative information.
 High speed of map generation.
50

Why photogrammetry……..
 Ideal technology when measuring objects such as
– Vast regions to be mapped
– Irregular shapes and
– Objects that are too
• Hot or cold
• Soft
• Delicate(very fine in texture)
• Inaccessible
• Toxic
• Radioactive to touch
51

Photogrammetric products
A.Planimetric maps –
Planimetric elements in geography are those features that
are independent of elevation, such as roads, building
footprints, and rivers and lakes. They are represented on
two-dimensional maps as they are seen from the air, or in
aerial photography. These features are often digitized from
orthorectified aerial photography into data layers that can
be used in analysis and cartographic outputs.
B.Topographic maps –
A type of map characterized by large-scale detail and
quantitative representation of relief, using contour lines.
Traditional definitions require a topographic map to show
both natural and man-made features. A topographic map is
typically published as a map series.
52

Photogrammetric products…..
 Photomap (Orthophotos)
 DEM/ DTM
 Virtual landscapes
 Nadir imagery is essential for mapping
 Overlap and side lap is required to give 3D information
 Note that
 Maps are the most prominent product of
photogrammetry.
 They are produced at various scales and degrees of
accuracies.
 Planimetric maps contain only the horizontal
position of ground features while topographic maps
include elevation data, usually in the form of contour
lines and spot elevations.
 Thematic maps emphasize one particular feature, e.g.,
transportation network.
53

1.4 Applications of photogrammetry
Topographical mapping:
• The plotting of map detail and contours is normally
carried out using aerial photogrammetric methods
• These methods are used for both original survey and
revision, and replace classical ground methods except
where the task is so small that flying is uneconomical
• The technique needs a certain amount of ground
surveyed control, but this requirement is being
continually reduced with the improvement of aerial
triangulation techniques to provide supplementary
control.
• A final Field check is necessary
54

Applications of photogrammetry
 Large Scale Plans:
• Large scale plans can be produced accurately and
quickly by air survey methods, but requires thorough
checking.
• by archaeologists to quickly produce plans of large
or complex sites
• by meteorologists as a way to determine the actual
wind speed of a tornado where objective weather
data cannot be obtained
• For large tasks such as road building and major
constructions, air survey methods are quicker and
cheaper than ground methods.
• profiles for determination of earthwork quantities can
be simply obtained using aerial photographs.
55

• Land use maps
• Hydrographical maps: mapping coast lines etc.,
• Exploration and reconnaissance
• Terrestrial and Scientific uses
– Detailed surveying of historic buildings
– Traffic accidents
– Medical applications etc.,
• Stereoscopic applications and measurements
56

• Cadastral Maps:
• Similar types and advantages compare to large scale
maps can be gained here.
• Ground techniques are accurate but not required in
all cases.
•Airphoto techniques provides necessary information
with adequate accuracy.
57

Check Points
 Discuss the photogrammetric applications in GIS. 5%
 Explain why photogrammetry is important field of study. 2%
 Explain the difference between photograph and Image.1%
 Explain the historical advancement of PGM. 4%
 Discus in brief, the phases of photogrammetry.5%
58

1.5 Basic Categories
► Photogrammetric Types from Applications Point
of View (d is distance from camera to object)
A. Close range d<10 m
B. Terrestrial Photogrammetry10 m<d<100 m
 Photographs are taken from fixed position on or
near the ground with camera distance settings to
finite values
C. Aerial Photogrammetry (Far range)2km<d<10
km
 Photographs are taken by a camera mounted in an
aircraft flying over the area with camera distance
setting to indefinite
D. Space Photogrammetry (Furthest Range) 30
km<d
59

Types of Photogrammetry…..
 Aerial and Space Photogrammetry
 Used for mapping Earth or planets
 Imaging system is based on an aircraft or spacecraft
 Target is the ground surface
 Image data is processed to create new spatial
information products
 Close range photogrammetry
 Used for industrial measurement
 Imaging system is handheld
 Target is the object being measured
 Image data is processed to make precise
measurements
60

Terrestrial Photogrammetry
Terrestrial:
62

Aerial Photogrammetry
Aerial Photo:
63

Space Photogrammetry
Space Photogrammetry:
64

Space Photogrammetry
Space Photogrammetry:
65

Activities
1.How archaeologists and meteorologists apply photogrammetry?
2.List and describe Photogrammetric Types from Applications Point of
view?
3.Discuss the relationship among RS,GIS, aerial photography and
photogrammetry.
4.Explain the evolution or historical development of Photogrammetry.
5.What are the most important products of photogrammetry?
6.Define photogrammetry.
7.Assume you are an expert of producing topographic map of Ethiopia. How
can you produce this extensive map?
66

Lesson 2. Camera
 most fundamental device in the field of photogrammetry
 It is the basic instrument which acquires images, from which
photogrammetric products are produced.
 Single-lens frame cameras are the most common cameras in
use today
 Imaging devices can be categorized according to how the
image is formed:
1.Frame cameras
2.strip cameras, linear array sensors, or pushbroom scanners
3.flying spot scanners or whiskbroom scanners
67

2.1. Principle design of aerial cameras
• Cameras are framing systems which acquire a snapshot of
an area (A), of the surface.
• Camera systems use a lens (B) (or system
of lenses collectively referred to as the optics)
to form an image at the focal plane (C), the
plane at which a film is placed and image
is registered.
• Cameras can be used on a variety
of platforms including ground-
based stages, helicopters, aircraft,
and spacecraft.
71

74
 Camera Body = houses camera driving mechanism, driving
monitor, operating handles and electrical connections, switches and
other accessories
 Film magazine – container of films
 Focal plane = all light ray through lens cone come to focus
 The focal length of the lens is the distance between the lens and
the image sensor.
 Diaphragm and Shutter regulate the amount of light which will
expose the photograph.
 Shutter controls the length of time that light is permitted to pass
through the lens.
 The lens cone assembly Contains the lens, shutter, and
diaphragm
 The filter serves three purposes:
 (1) It reduces the effect of atmospheric haze,
 (2) it helps provide uniform light distribution over the entire
format, and
 (3) it protects the lens from damage and dust.

2.2. Internal camera geometry
• Lens: the most important and expensive component and is
used for projecting an optical image onto the film.
• Focal length (principal distance) together
with the flying height, it determines the photo
scale.
• The focal length also determines the angle
of view of the camera and determines the area "seen" by the
camera.
• Position of principal point is defined by fiducial marks,
mounted on the frame of the camera.
• Fiducial marks are also
required to align(arrange) photos
for stereoviewing.
75

Photo Scale
 Map scale
 S (Scale) = MD (Map Distance)/GD (Ground Distance)
 Photo Scale
 S = PD (Photo Distance)/GD
77
(When Computation of scale from terrain level).
(When the ground elevation is at sea level, h becomes zero)

2.3.Types of Camera
Types of Camera:
 Aerial cameras can be classified in a number of ways:
1. By lens type: single lens, multiple lens.
2. By angular field: normal angle-up to 75ᵒ; wide angle-
75ᵒ to 100ᵒ;and, super wide angle-100ᵒ and above.
3. By focal length: short-up to 6 inches; normal-6 to 12
inches; and, long-more than 12 inches.
4. By use: reconnaissance, mapping and special
78

Check Points and Assignment 2 (25%)
1.Name and briefly describe the main parts of a frame aerial
mapping camera.4%
2. List and briefly describe the three geometric categories of
imaging devices.4%
3. Explain why photogrammetry is important field of study.
2%
4. Explain the difference between photograph and Image.1%
5. Explain the historical advancement of PGM. 4%
6. Discus in brief, the phases of photogrammetry.3%
7. Discuss the difference among ground based, aerial and
Space photographs.3%
8. Explain the advantages of aerial photographs.2%
9. Discuss the difference between swath and nadir.2%
79

Lesson 3.Aerial Photography
 The term "photography" is derived from two Greek
words meaning "light"(photo) and "writing" (graphien).
 Photography is production of permanent images by means of
the action of light on sensitized surfaces (film or array inside
a camera), which finally giving rise to a new form of visual
art.
 Aerial Photography means photography from the air
 Aerial photography is the taking of photographs of the
ground from an elevated/direct-down position.
 Usually the camera is not supported by a ground-based
structure 80

 Platforms for aerial photography include:
 fixed-wing aircraft,
 helicopters,
 multirotor Unmanned Aircraft Systems (UAS),
 balloons,
 blimps and dirigibles (airships),
 rockets, pigeons, kites, parachutes, stand-alone
telescoping and vehicle-mounted poles.
 Mounted cameras may be triggered (cause to function)
remotely or automatically; hand-held photographs may be
taken by a photographer.
81

Aerial photography ……
Note Aerial photography should not be confused with air-to-
air photography, where one or more aircraft are used as chase
planes that "chase" and photograph other aircraft in flight.
83

Historical Background of Aerial photography
Read Historical Background of photogrammetry.
Assignment two
1.Discuss the history of Aerial photography.
2.Discuss the difference among ground based, aerial and
Space photographs.
3.Explain the advantages of aerial photographs.
4.List the components of aerial camera.
5.Discuss the difference between swath and nadir.
84

3.2 Advantages of Aerial Photography
 Advantages of Aerial Photography over Ground-Based
Observation:
 Aerial photography offers an improved vantage point.
 Aerial photography has the capability to stop action.
 It provides a permanent recording.
 It has broader spectral sensitivity than the human eye.
 It has better spatial resolution and geometric fidelity
(reliability) than many ground-based sensing methods.
85

3.3 Applications of Aerial Photography…..
 Applications of Aerial Photography:
 Land-Use Planning and Mapping
 Geologic Mapping
 Archaeology
 Species Habitat Mapping
 Integration of Aerial Photography into GIS
 Digital Image Processing
86

3.4 Characteristics of Aerial Photography…
1. Synoptic Viewpoint:
 Aerial photographs give a bird's eye view of large areas
enabling us to see surface features in their spatial context
(general view of a whole).
 They enable the detection of small scale features and
spatial relationships that would not be found on ground.
87

Characteristics of Aerial Photography…
2.Time freezing ability:
 They are virtually permanent records of the existing
conditions on the Earth’s surface at one point in time, and
used as an historical document.
3. Capability to stop action:
 They provides a stop action view of dynamic conditions
and are useful in studying dynamic phenomena such as
flooding, moving wildlife traffic, oil spills, forest fires
88

4.Three dimensional perspective:
 It provides a stereoscopic view of the Earth’s surface and
make it possible to take measurements horizontally and
vertically
 a characteristic that is lacking for the majority of remotely
sensed data.
5. Spectral and spatial resolution:
 Aerial photographs are sensitive to radiation in
wavelengths that are outside of the spectral sensitivity of
the human eye (0.3 μm to 0.9μm versus 0.4 μm to 0.7 μm).
89

6.They are sensitive to objects outside the spatial resolving
power of human eye.
7. Availability:
 Aerial photographs are readily available at a range of
scales for much of the world.
8. Economy:
 They are much cheaper than field surveys and are often
cheaper and more accurate than maps.
90

3.5 Types of aerial photographs
• Two types:
 Vertical aerial photographs( Axis of camera vertical < 3˚)
 Oblique aerial photographs(Axis of camera inclined to vertical line
> 3˚)
• Photographs that are tilted less than 3° off the vertical
are regarded as vertical.
•
91

Cont…
92
Camera axis < 3° inclined by 30° tilted by 60°

Cont…
•Vertical aerial photographs:
 Lens axis is perpendicular to the surface.
 It covers a relatively small area.
 The ground area covered by a single photograph
approximates the shape of a square or rectangle.
 Relief is not readily apparent.
 Distances and directions vary across the photograph
unless the ground is flat.
 It provides a bird’s-eye view of the area which is not the
normal view experienced by people in the area.
94

Types of aerial ...
• Oblique photographs are taken with the angle from the
vertical deliberately set somewhere between 3° and 90°.
•
95

Cont…
•They are termed
 low oblique if the horizon is not visible on the photograph
 high oblique if the horizon is visible.
• Low oblique photographs:
 The camera lens system is inclined by usually 30°.
 Covers a relatively small area.
 The ground area covered is trapezoidal
although the photograph is square.
Since scale varies over the photograph,
distances and directions are not true.
 Relief can be seen but it is distorted.
 The horizon is not visible.
 The objects have a more familiar view which resembles the view
the observer would get from a high vantage(places affording good
view) point such as a hill or the roof of a high building.
96

Types of aerial ...
• High oblique photographs:
 The camera is tilted about 60° from the vertical.
 The horizon is always visible.
 It covers a very large area.
 The ground view is trapezoidal
though the photograph is square.
 Familiarity of the view varies
depending on the height from which
the photograph was taken.
 Scale is variable therefore distance and directions on the
photograph are not true.
 Relief can be seen but it is sometimes distorted.
97

Types of aerial photographs:
In general we have two major Types of photographs
(categorized by tilt)
98

Types of aerial photographs:
99

Fig. Geometry of vertical, oblique and horizontal
photographs.
100
VERTICAL LOW OBLIQUE HIGH OSLIQUE HORIZONTAL

• Advantages of vertical photographs over oblique
 Vertical photographs give approximate uniform scale over
the photograph but oblique photos do not.
 Measuring distances and directions on vertical photos are
therefore easier and more accurate.
 In flat areas the vertical photos can almost be used as a
map.
 Since scale of the vertical photos is nearly constant, scale
and directions can be measured in the same
way as those on a map.
 Limited geometric distortions.
 Stereoscopic study on vertical photos
is more effective than on oblique photos.
Constant scale makes interpretation easier and tall buildings
do not hide data as they do on oblique photos.
101

• Advantages of oblique photographs over vertical
 Oblique photos give a more natural view of ground features
especially buildings, bridges etc.
 Oblique photos cover more ground area than vertical
photos from the same altitude and focal length.
 Oblique photos can give cover in areas where low cloud
might obscure(hidden) the ground using vertical photos.
 Determination of feature elevations is more accurate on
oblique photos than on vertical photos.
 Cameras can be cheaper since
photography not used for precision
photogrammetry.
 Tree canopy or other tall buildings
can mask detail on vertical photos which may be visible on
oblique photos.
102

3.6 Taking vertical aerial photographs
• When taking vertical aerial photographs, the aircraft
flies in a series of lines, each called a
flight run (A).
• Photos are taken in rapid succession
looking straight down at the ground,
often with a 60% overlap between next photos.
• The overlap ensures total coverage along a flight line
and also facilitates stereoscopic viewing.
•.
103

Lateral or Side overlap(Side Lap) and Forward Overlap (End Lap))
104
Lateral Overlap (Side Lap) Forward Overlap (End Lap)

TakingVertical Aerial Photograph
Tips!!
106

Basic geometry of a vertical aerial
photograph.
107

Illustration of imaging for a nadir-viewing camera
108

Focal Length, Coverage and Quality
 Focal length and quality of photo has direct relation
 Focal length and coverage has invers relation.
 Coverage = F(f,Al and Format of camera)
109

3.7 Stereo pair of photographs
• Successive photo pairs display the overlap region from
different perspectives and
• can be viewed through a device called a stereoscope to
see a three-dimensional view of the area, called a stereo
model.
• Two next images form a stereopair
(A)+(B) which allows to perceive a
stereo model within overlapping area
(C).
• Single image allows to measure planimetric (X,Y)
coordinates of an object.
• Stereopair allows to retrieve 3D coordinates (X,Y,Z) of
the object.
110

Overlap Between Runs
30% overlap between
runs or swaths
111
Run #1
Run #2

Presentation Assignment
1. Describe the difference between nadir and swath 1%
112
2.What is the primary difference between high and low
oblique aerial photographs? 1%
3. Define the following photogrammetric terms: end lap,
side lap, stereopair, exposure station, and flying height. 1%
4. Discuss the importance of photogrammetry in geographic
information systems. 3%
5. Presentation 4%

3.8 Photographic scale
• The amount of detail shown in an aerial photograph is
dependent, among other things, on the scale of
photograph.
• “photograph scale” is an expression that states one
unit / any unit/ of distance on a photograph represents a
specific number of units of actual ground distance.
• Scales may be expressed as unit equivalents,
representative fractions, or ratios.
1mm = 25m ( unit equivalent), or
1/25,000 (Representative Fraction), or
1:25,000 (Ratio).
• The scale of a vertical photograph approximately
equals to the ratio of the flying height above the ground
(H) and the focal length of the camera lens (f).
113

• For a vertical photograph taken over flat terrain, scale
is a function of the focal length (f) of the
camera used to acquire the image and
the flying height above the ground (H)
from which the image was taken.
114
H
f
S 
ave
ave
h
H
f
S


• If the photographed terrain varies in
elevation, object distance will also vary
and photo scale will like wise vary.
• Photo scale increases with increasing
terrain elevation and decreases with
decreasing terrain elevation.

3.10. Image Displacement
 The difference between an accurate planimeteric
map and a vertical aerial photograph lies in the
fact that the former depicts all features at their
correct horizontal position whereas the images on
the latter are generally displaced from their true
plane position because of (causes of image
displacement):
 (i)Photographic deficiencies ;
 (ii) Ground relief ;
 (iii) and Tilt of the camera.
115

cont
3.11. Displacement due to Photographic Deficiencies
 Displacement due to photographic deficiencies can be
caused by:
 inferior lens,
 faulty assemblage of camera,
 faulty shutter,
 film shrinkage and
 the failure of the film-flattening mechanism at the
camera focal plane.
 These deficiencies may result in a noticeable lack of
sharpness in the images
116

3.12. Relief Displacement
•.
117
• The figure shows displacement due to relief in a single
photograph. (A) as the photograph is taken, (B) as the
photograph appears.
 Variations in ground relief is the most significant source of image
displacement on vertical aerial photographs.
 The image of any feature lying above or below the horizontal ground
surface (datum plane) would be displaced on a vertical aerial photograph
from its true plan position.

cont
 Relief displacement is the shift or displacement in the
photographic position of an image caused by the relief
of the object, i.e., its elevation above or below a
selected datum.
 This displacement is outward for objects above the
datum and inward for objects below the datum
d = relief displacement (mm)
r = radial distance from nadir (mm)
h = height of the terrain above reference plane (m)
H = flight altitude above reference plane (m)
118

cont
• The direction of displacement is Radial from the Nadir(N)
of the photograph
• In a truly vertical photograph where nadir (N) coincides
with principal point (PP) of the photograph, the following
facts will hold good:
1.The topographic displacement varies directly with the height
of the object and the distance between the object and the
principal point (nadir).
2.Relief displacement is radial from the nadir and all objects of
the same height and equidistance from the nadir in any
direction will be displaced the same amount.
3.There is no displacement at nadir.
4.Objects projecting above a selected datum are displaced
radially outward from the optical centre of the photo principal
point (PP) on a line passing through the true plane position of'
the object.
119

cont
5.Relief displacement varies inversely with the height of
the photography. Greater will be the flying height lesser
displacement:
6.Relief displacement varies directly with the height of
the object. Taller objects are displaced more than shorter
objects.
120

• As the distance from the principal point increases, the
relief displacement increases.
• Objects not under the principal point will lean
outward.
• Towers A and B are equally high, but placed at
different distances from the nadir point, thus have
different relief displacements.
• Objects directly below center
of camera lens (i.e. at the nadir)
will have only their tops visible.
121
• Relief displacement increases
as the elevation of the point
increase.

3.13 Image Parallax
• Image Parallax is an apparent displacement of an object when seen from
two different points.
•In case of aerial photographs an object is viewed or photographed from
two different positions.
•Consequently, an apparent shift in the position of that object takes place,
which is referred to as parallaxes displacement.
•Parallax refers to the apparent change in relative positions of stationary
objects caused by a change in viewing position.
• The change in position of an image from one photograph to the next
caused by the aircraft’s motion is termed stereoscopic parallax or simply
parallax.
• Parallax of any point is directly related to the elevation of the point, and
that parallax is greater for high points than low points.
• Variation of parallax with elevation provides the fundamental basis for
determining elevations of points from photographic measurements (3D
view).
122

cont
 Types of Parallax
 Parallax is of two types:
1. Absolute parallax (X-parallax) –
 displacement along or parallel to the line of flight and
is represented by the algebraic difference of the
distances of corresponding images from their
respective nadirs when measured parallel to the line of
flight.
2. Y-parallax –
 displacement at right angles to the line of flight.
 Y-parallax is not commonly used in aerial
photography for forestry purposes
124

• The absolute stereoscopic parallax (x-parallax) P at a
point is defined to be the algebraic difference, measured
parallel to the line of flight, of the distances of the two
images from their respective principal points.
125
• Displacement in stereoscopic
pairs of photographs. A) as the
photographs are taken, B) as
the photos appear. Similar
triangles are used to derive the
basic parallax formula .
where:
h = height of object
H = flying height of the aircraft above
the base of the object
P = absolute stereoscopic parallax at
the base of the object
dP = parallax difference between the top of the object and the base of the
object.

• Aerial photographs have the following advantages over
maps:
 It provides a current pictorial view as opposed to a
symbolic representation of the survey area
 It is more readily obtained, the mapping process
which often includes aerial photography, can take
months to complete.
 It can be used to provide information of inaccessible
areas.
 It shows things that are often omitted from maps.
 It provides a permanent synoptic(wide view) record
of an area which can be used to compare with earlier
or later photographs to monitor changes in an area.
126

• The following are disadvantages of photographs
compared to maps:
Position location and scale are only approximate.
Ground features are difficult to identify or interpret
without the symbols that appear on maps
Some features are obscured(being out of sight) by
other ground detail, buildings in forests for example.
Obtaining relief information requires stereoscopic
overlapping photographs and a stereoscope.
The absence of contrasting colour or tone makes
interpretation difficult in poor lighting conditions.
There is no marginal data to assist in its
interpretation.
It requires skill and training to use effectively.
127

4. Air photo Interpretation
• Aerial photographs contain a detailed record of features
on the ground at the time of data acquisition.
• Photographic interpretation is the act of examining
photographic images for the purpose of identifying
objects and judging their significance.
• Success in photo interpretation varies with:
 training and experience of the interpreter
 nature of the objects or phenomena being interpreted
quality of the photographs being utilized
• A photo interpreter systematically examines the photos
and, frequently, other supporting materials such as maps
and reports of field observations.
128

4.1 Elements of Airphoto Interpretation
• A systematic study of aerial photographs usually
involves several basic characteristics of features shown
on a photograph.
• The exact characteristics useful for any specific task
depend on the field of application.
• Most applications consider the following basic
characteristics, or variation of them:
 Shape
 Size
 Pattern
 Tone
 Texture
 Shadow
 Site
 Association
129

i. Shape: refers to the general form, configuration, or
outline of individual objects.
• Many features possess characteristic shapes that
readily identify the features.
• In the case of stereoscopic photographs, the object’s
height also defines its shape.
• Anthropogenic features usually appear as straight or
smooth curved lines, while natural features usually
appear to be irregular.
• Some of the most prominent man-made features are
highways, railroads, bridges, canals, and buildings.
• For example, a railroad is usually readily distinguished
from a highway because its shape consists of long
straight tangents and gentle curves as opposed to the
curvy shape of a highway.
130

131
This is a baseball diamond next to a track and field area.

ii. Size: of objects on photographs must be considered in
the context of the photo scale.
• In the use of size as a diagnostic characteristic both the
relative and absolute sizes of objects can be important.
• The size of objects can be important in discrimination of
objects and features (cars vs. trucks or buses; bush vs.
trees, etc.).
• The size of unknown objects on a photograph, as
determined from the scale of the photograph or a
comparison with known objects of known size, gives a
clue to their identity.
• For example, in a built-up area the smaller buildings are
usually dwellings, and the larger buildings are
commercial or community buildings.
132

iii. Pattern: relates to the spatial arrangement of objects.
• It is the regular arrangement of objects that can be
diagnostic of features on the landscape.
• The repetition of certain general forms or relationships
is characteristic of many objects
• Both man made & natural gives objects a pattern that
aids the photo interpreter in recognizing them.
• Pattern can be either man-made or natural.
• Pattern can also be very important in geologic or
geomorphologic analysis.
• Example, drainage pattern can tell the trained observer
a great deal about the lithology and structural patterns in
an area.
133

134
Pattern is another
principle that helps us
identify trees.
The man-made
patterns of fields,
orchards, and roads
contrast with
nature's patterns of
river and forest.

iv. Tone (colour): refers to colour or relative brightness
of objects on photographs.
• Tone can be defined as each distinguishable variation
from white to black.
• It is related to reflectance of light from objects.
• With out tonal differences, the shapes, patterns, &
textures of objects could not be discerned or detected.
135

v. Texture: is the frequency of tonal change on the
photographic image.
• It is a product of their individual shape, size, pattern,
shadow, and tone.
• As the scale of the photograph is reduced, the texture
of any given object or area becomes progressively finer
and ultimately disappears.
• An interpreter can often distinguish between features
with similar reflectance based on their texture
differences.
• An example would be the smooth texture of green
grass as contrasted with the rough texture of green tree
crowns on medium scale aerial photos.
136

vi. Shadows: are important to interpreters in two
opposing respects:
 the shape or outline of a shadow affords an impression of
the profile view of objects (which aids interpretation), and
 objects within shadows reflect little light and are difficult to
discern on photographs (which hinders interpretation)
• Shadows are very helpful in identifying features since
they show the familiar side view of the object.
• Some excellent examples are the shadows of water
towers or cooling towers and bridges.
• When viewed directly from above, only a round circle
or dot is seen, whereas the shadow shows the profile
and helps to identify the object.
• Relative lengths of shadows also usually give a good
indication of relative heights of objects; however the
length of a shadow will also depend on other factors
such as the time of day and year.
137

141
• Bridge (Shadow): Shadow is
another principle of photo
interpretation.
• An object's shadow often
gives us as much information
as the object itself.
• On this larger scale photo, it's
easy to see the design of the
steel superstructure and the
piers by looking at the
shadows.

vii. Site: refers to topographic or geographic location
and is particularly important aid in interpretation.
• Agricultural crops may like certain conditions.
• Man made features may also be found on rivers (e.g.
power plant) or on a hill top (observatory or radar
facility).
• For example, certain tree species would be expected to
occur on well-drained upland sites, whereas other tree
species would be expected to occur on poorly drained
lowland sites.
• Various tree species occur only in certain geographic
areas (e.g., “teff” occurs in “Kolla” but not in “Dega”).
142

viii. Association: refers to the occurrence of certain
features in relation to others.
• Quite often an object not easily recognized by itself
may be identified by its relative position to surrounding
objects.
• Naturally some features are found in association with
others.
• For example, a church with its compound might be
difficult if it is located in a forest, but would be easy to
identify if it is sited in an area of low forest cover.
• Schools at different levels typically have characteristic
playing fields, parking lots, and clusters of buildings in
urban areas.
143

144
This is an air port because
of its shape and because
there are air planes.

4.2 Airphoto interpretation keys
• Two general types of airphoto interpretation keys exist:
 Selective key
 Elimination key
• A selective key: contains numerous photographic
examples with supporting text.
• The interpreter simply selects that example that most
closely corresponds to the object he/she is trying to
identify, e.g. industries, landforms, etc.
• An elimination key: takes a hierarchical structure of a
set of alternatives in which the interpreter eliminates
various criteria from the classification.
• The interpreter follows a precise step-wise process that
leads to the elimination of all items except the one
(ones) that he/she is trying to identify.
145

4.3. Airphoto Interpretation Equipment
• Stereoscope: is an instrument which facilitates the
stereo viewing process.
146
Mirror stereoscope
Lens stereoscope
• Many applications of
aerial photography use
stereoscopic coverage
and stereo viewing.

Airphoto Interpretation Equipment
Tips!
Types of air photo interpretation:
1.Lens Type Stereoscope - is the simplest optical instrument for
viewing objects in three dimensions.
2.Prism Type Stereoscope - consists of two thin prisms which are
fixed in a stand and are used for viewing stereo-pairs.
3. Mirror Type Stereoscope(reflecting stereoscope) - The
superiority of this stereoscope over the other two types of
stereoscopes lies in the fact that it affords full separation of the
stereoscopic pair of photographs.
 And provides full view of the entire stereoscopic model under
normal observing (no magnification) conditions
147

5. Orthophoto
• Orthophoto combines the image characteristics of an
aerial photograph with the geometric qualities of a map.
• Unlike normal aerial photographs, distortions and
relief displacement are removed so ground features are
displayed in their true planimetrically correct position.
• Orthophotography is the process of making an
orthophoto.
• Accurate measurements of distance, area and
directions can be made, however
should not be used for detailed
photo interpretation due to a loss
in resolution.
148

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