This document discusses aerial photogrammetry and provides definitions of key terms. It describes how aerial photographs are taken from aircraft and used to create topographic maps. The process involves establishing ground control points, planning flights and photography with proper overlap, interpreting photographs, using stereoscopes to view overlapping image pairs in 3D, and constructing maps through cartography. Precise measurement of ground coordinates is enabled through analyzing parallax differences between corresponding points in stereoscopic image pairs.

1. AERIAL PHOTOGRAMMETRY
MODULE - IV
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By
Abdul Mujeeb
Asst Prof.
Dept Civil Engineering
KVGCE

2. Photogrammetry
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3. Photogrammetry
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4. Photogrammetry
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21. Aerial Photogrammetry
•It is branch of Photogrammetry wherein photographs
are taken by camera mounted in aircraft flying over
the area.
•Mapping from this best mapping procedure for large
projects.
•Major users are civilian and military mapping
agencies of government.
• Used successfully for maps varying in scale from 1:1,00
0,000 1:120 with contour intervals as small as 1 foot.
• Topographic mapping is the most common form. – U.S.
G.S updated and done this way.
• Used to reconstruct a scaled 3-dimensional optical mode
l of the lands surface using a stereoplotter.
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25. Topographic mapping
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26. Architectural drawings from photogr
aphic measurements
Then Now 26

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28. Close range photogrammetry
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32. Orthophotographs
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33. Comparison of Map and Orthophot
ograph
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35. Engineering Construction
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37. Aerial Camera
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38. Essential Parts
• Lens Assembly-Lenses, Diaphragm,
Shutter and filter
• The camera cone
• Focal plane
• Camera body
• Drive mechanism
• Magazine
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39. Shutter- Controls interval of time during which
light is allowed to pass through lens.
Diaphragm- Placed between lens elements and
acts as physical opening of lens system. Can
be rotated to increase or decrease size of
opening to control rays to pass through lens.
Filter- Colored glass placed in front of lens to
filter stray light in atmosphere and also flying
particles.
Camera cone-Supports entire lens including
the filter 39

40. Focal plane-Collimation marks at upper
surface of the cone.
Camera body- Part of camera provided at top
of cone.
Drive mechanism- It is housed in camera body
and is used for winding, tripping the shutter,
operating vacuum system for flattening film,
winding the film.
Magazine- Holds exposed and unexposed
films and houses the film flattening device at
focal plane. 40

41. Aerial Camera
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42. Definitions
►Vertical photograph-Made with camera axis coinciding
with direction of gravity
►Tilted photograph- Made with camera axis
unintentionally tilted from vertical by small amount
(less than 3°)
►Oblique photograph- Made with camera axis directed
intentionally between horizontal and vertical.
►Perspective projection- It is produced by straight lines
radiating from common point and passing through
point on the sphere to plane of projection
(Ex:Photograph)
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44. ►Exposure station (o) : The point in the atmosphere
occupied by center of camera lenses at instance of
photography.
►Flying height : Vertical distance between exposure
station and mean sea level or any other datum.
►Flight line: Line traced by exposure station in
atmosphere ( track of aircraft)
►Focal length-It is distance between nodal point of lens
to plane of photograph(OK)
►Photo principal plane (k) It is point on photograph
obtained by projecting camera axis to intersect at a
point on photograph known as photo principal point(k)
►Camera axis extended up to ground, the point
obtained on ground is called Ground Principal point (K)44

45. ►Plane defined by lens(O), ground nadir point (N) and
principal point produced to ground (K) ie plane NOK
►Nadir point (n)- Point where plumb line dropped front
nodal point intersects photograph
►Photo nadir point (N) : It is a point on photograph
obtained by dropping vertical line from camera center.
That plumb line extended up to ground gives Ground
Nadir Point (N)
►Tilt- Vertical angle by intersection at exposure station of
optical axis with plumb line- (angle kon=t )
►Principal line- Is the line of intersection of principal plane
with plane of photograph. Line joining principal point and
photo nadir point. (nk)
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46. ►Isocentre- Is the point in which bisector of angle of tilt
meets the photograph(oi). Isocentre lies on principal line at
distance of f*tan(t/2). In vertical photograph Isocentre and
photo nadir point coincide with principal point.
►Azimuth : (A) : Clockwise horizontal angle measured about
ground nadir point from true north to the principal plane of
photograph.(Ф )
►Swing (S) :-Angle measured in plane of photograph from +y
axis clockwise to photo nadir point.
►Horizon point (h) : It is point of intersection of horizontal
line through center of lenses and principal line (np) on
photograph.
►Axis of tilt:- It is line in plane of photograph perpendicular
to principal line at the Isocentre (i1 i i2)
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53. A vertical photograph
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57. An oblique photograph
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59. SCALE OF
VERTICAL PHOTOGRAPH
►Photograph is perspective projection, images of ground
points are displaced where there are variations in
ground elevations.
►Therefore there is no uniform scale between points on
photograph except points are at same elevations.
►If elevations of points vary, scale of vertical photograph
will vary from point to point on photograph.
► when ground is horizontal, all points having same
elevation, S=scale=map distance/ground distance
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63. Ground Co-ordinates
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66. • We have seen that if the photograph is truly vertical and
the ground is horizontal,
• the scale of the photograph ,will be uniform. Such a
photograph represents a true orthographic projection
• In actual practice, however, such conditions are never
fulfilled.
• When the ground is not. horizontal. the, scale of the
photograph varies from point to point and is not constant.
Since the photograph is perspective view, the ground relief
is shown in perspective on photograph.
• Every point on the phototroph is therefore displaced from
their true orthographic position. This displacement is
called relief displacement.
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73. OR LENGTH FROM GROUND CO-ORDINATES
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77. Procedure of Aerial Survey :-
The procedure of aerial survey consists of the followings
sections:
a) Establishing ground control
b) Flight planning and photography- Overlap
c) Photo interpretation
d) Stereoscopy
e) Construction of map and cartography
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78. • Ground control survey includes locating points on the
ground which can be identified on aerial photographs
• It is essential to establishing and orientation of photographs
on ground.
• Ground control extent depends on scale of map, navigation
control and cartographical process of producing maps
• Establishing ground points is divided in to 2 parts
(a) Basic control (b) Photo control
• Basic control- establishing triangulation stations, traverse
stations, azimuth marks, benchmarks etc.
• Photo control- establishing horizontal or elevations of
identified points in photograph w.r.t to basic control.
• These control introduces horizontal control and vertical
control- basic horizontal and vertical control, horizontal and
vertical photo control respectively
Establishing Ground Control
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79. • Elevations of vertical control points- carrying levels from
benchmarks.
• Horizontal photo control points are located w.r.t basic
control by third fourth order triangulation, third order
traversing, trigonometric levelling etc.
• Vertical photo control points are located by third order
leveling, fly leveling etc.
• Established in 2 methods (a) Post-marking (b) Pre-marking
• (a) Post-marking method- photo control points are selected
after aerial photography. Advantage- positive identification
and favorable location of points.
• (b) Pre-marking- photo control points are selected first &
then included in photograph.
• Marks on ground should be marked with paints, flags etc so
that they can be easily identified on photograph. 79

80. Flight planning consists of the following information :-
a) The area to be surveyed
b) Focal length of the camera
c) Scale of the photograph
d) Longitudinal and side overlap
e) Approximate ground speed of the aircraft in stable air.
The above information is required to find the altitude of the
aircraft above datum, time interval between the exposures, the
area covered by each photograph, number of photographs
number of strips and air base. To cover the entire terrain to be
surveyed, sufficient photographs with suitable overlap should
be taken.
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81. • When maps are prepared from
vertical photographs, plumb
points of preceding and succee
ding prints should visible in
each photograph.
• Photographs are taken in
intervals along each strip such
that desired overlap is obtained
in each strip.
• Strips are placed at
predetermined distances to get
desired overlap.
• Overlap of photograph in the di
rection of flight line is called
Overlap
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82. • Overlap of photograph in the
direction of flight line is called
longitudinal or forward or simply
overlap.
• Frequency of photography is
such a way that successive photo
graph have overlap of 55-65%.
• Fig shows flight lines and
longitudinal overlap having
overlap more than 50% and
alternate photograph having
overlap by another 10-30%.
• Overlap between adjacent flight
line is called lateral overlap or
side overlap. Side overlap is
about 15-35%.
• Fig shows overlap
between three flight
lines 82

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84. Photographic interpretation
• Photographic interpretation means identifying and
recognizing objects in the aerial photograph and then
judging their significance in photograph.
• Applications- Identification of land form, study of site
conditions, density and type of vegetation cover, location of
site for boreholes etc.
• Oblique photos- easy to interpret- pictorial form
• Color photo- easy
• Requires training, experience, imagination, patience,
observation
• Characteristics of photo images- Shape , size, pattern,
shadow, texture, site (surroundings).
• Photo interpretation is done with using magnifiers.
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85. Stereoscopy and Parallax
•Stereoscopic vision- similar to
binocular vision, enables observer
to view an object or to be more
precise, 2 different perspectives of
an object, so as obtain mental
impression of 3 dimensional
image.
•Stereoscopic vision- third
dimension i.e. depth or height is
obtained by principle of parallax.
•Angle of Parallax- Apparent
movement of a point viewed first
with one eye and then with another
is known as parallax.
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87. Stereoscopic Fusion
• Principle of this vision can be applied to photogrammetry.
• If pair of photographs of objects are taken at two different
positions of camera and then viewed by an apparatus, in
which left eyes sees only left hand picture and right eye sees
only right hand picture. These 2 separate images are fused
together in brain to provide observer with spatial impression
• This is known as stereoscopic fusion and pairs of two such
photographs is known as stereopair.
• Devices used this are stereoscope and anaglyph.
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88. Stereoscope
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89. Anaglyph
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90. Stereoscope
• It is an instrument used for viewing stereopairs.
• They are designed for 2 purposes
1. Assist in presenting to the eyes of observer,the images of
pair of photographs so that it object in photograph visible
as same as it be natural vision.
2. To magnify the perception of depth.
• Two basic types of stereoscope are
(1) Mirror stereoscope (2) Lens stereoscope
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91. Mirror Stereoscope
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92. • Consists of small eye-
piece mirrors m and mꞌ
and M and Mꞌ which is
oriented 45° with plane of
photograph.
• Fig shows nail mounted
on timber block.
• Lens is kept first in
position of left eye and
then right eye,
photographs are taken.
• In photo head of nail is at
different positions
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93. • 2 negative prints are
placed in stereoscope.
• Images of nail are only
observed.
• Four mirrors transfer light
to eyes exactly as if it had
come from nail as shown
by dotted line.
• Convergence and retinal
disparity enables observer
to see nail in 3 dimensions
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94. Lens Stereoscope • Consists of single
magnifying lens for each
eye and no mirrors.
• Distance between 2 lenses
can be varied according to
distance between eyes of
observer.
• Distance between nodal
point and photograph
depends upon focal length
of lens.
• Disadvantage- strain to
eyes.
• Advantage- small in size,
easy to carry 94

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96. Parallax
• Parallax of a point is displacement of a image of
point in 2 successive exposures.
• Difference between displacements of images of two
points on successive exposures is called difference
in parallax.
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98. • This point to point difference in parallax between
points of stereopairs makes possible to view photos
stereoscopically to get impression of 3 dimensional
image of a terrain.
• Ideal conditions for getting aerial stereoscopic views
of ground surface
1. 2 photographs taken with suitable overlap
2. Elevations of camera positions remains same for
two exposures
3. Camera axis is vertical so that picture plane lies in
the same plane of horizontal plane.
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103. • Vertical photograph can be fitted together to form map like
photograph of ground.
• Getting series of such overlapping photographs is called
mosaic.
• It is a map substitute to varying degree of accuracy.
• If photographs are taken at different altitudes they do not fit
well. It is best to re-photograph to bring to proper scale.
• Controlled mosaic is obtained when photographs are
carefully assembled so that horizontal points agree with
previously plotted points.
• Uncontrolled mosaic- Assembled without any regards of
control.
• Index mosaic- photograph laid in sequence as to allow photo
number and flight number on finished assembly. It is form
of uncontrolled mosaic
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105. THANK YOU
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