Short Notes for Remote Sensing Photogrammetry GIS & GPS | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


Photogrammetry
Introduction
Photogrammetric surveying or photogrammetry is the sci-
ence and art of obtaining accurate measurements by use of 
photographs, for various purposes such as the construction 
of plainmetric and topographic maps, classifi cation of soils, 
interpretation of geology, acquisition of military intelli-
gence etc. The scale and fl ying height concepts of photo-
grammetry are focused in this chapter.
De? nitions
 • Vertical photograph: It is an aerial photograph made 
with the camera axis (or optical axis) coinciding with the 
direction of gravity. 
 • Tilted photograph: It is an aerial photograph made with 
the camera axis unintentionally tilted from the vertical by 
a small amount (< 3
0
).
 • Oblique photograph: This is also an aerial photography 
taken with camera axis tilted intentionally. If the horizon 
is shown in the photograph, it is said to be high oblique. 
If the apparent horizon is not shown, it is said to be low 
oblique.
 • Terrestrial photogrammetry: Photographs taken from a 
fi xed position on or near the ground.
 • Aerial photogrammetry: Photographs are taken from a 
camera mounted in an aircraft fl ying over the area.
 • Phototheodolite: It is a combination of theodolite and 
terrestrial camera.
 • Camera axis: Line passing through centre of camera lens 
perpendicular both to camera plate (negative) and picture 
plane (photograph).
 • Picture plane: Positive plane, perpendicular to camera 
axis.
 • Principal point: Point of intersection of camera axis with 
either picture plane or the camera plate.
 • Focal length: Perpendicular distance from centre of 
camera lens to either to picture plane or camera plate. It 
satisfi es the relation
11 1
fu v
f
uv
uv
==+? =
+
 
 • Nodal point: It is either of two points on the optical 
axis of a lens so located that when all object distances 
are measured from one point, and all images distances 
are measured from other. They satisfy the simple lens 
relation
11 1
fu v
=+
 • Principal plane: It is a plane which contain principal line 
and optical axis.
 ? Photogrammetry
 ? Remote sensing
 ? Geographic information system (GIS)
 ? Global positioning system (GPS)
CHAPTER HIGHLIGHTS
Remote Sensing, 
Photogrammetry GIS and GPS
Part III_Unit 12_Chapter 06.indd   1 5/31/2017   4:55:30 PM
Page 2


Photogrammetry
Introduction
Photogrammetric surveying or photogrammetry is the sci-
ence and art of obtaining accurate measurements by use of 
photographs, for various purposes such as the construction 
of plainmetric and topographic maps, classifi cation of soils, 
interpretation of geology, acquisition of military intelli-
gence etc. The scale and fl ying height concepts of photo-
grammetry are focused in this chapter.
De? nitions
 • Vertical photograph: It is an aerial photograph made 
with the camera axis (or optical axis) coinciding with the 
direction of gravity. 
 • Tilted photograph: It is an aerial photograph made with 
the camera axis unintentionally tilted from the vertical by 
a small amount (< 3
0
).
 • Oblique photograph: This is also an aerial photography 
taken with camera axis tilted intentionally. If the horizon 
is shown in the photograph, it is said to be high oblique. 
If the apparent horizon is not shown, it is said to be low 
oblique.
 • Terrestrial photogrammetry: Photographs taken from a 
fi xed position on or near the ground.
 • Aerial photogrammetry: Photographs are taken from a 
camera mounted in an aircraft fl ying over the area.
 • Phototheodolite: It is a combination of theodolite and 
terrestrial camera.
 • Camera axis: Line passing through centre of camera lens 
perpendicular both to camera plate (negative) and picture 
plane (photograph).
 • Picture plane: Positive plane, perpendicular to camera 
axis.
 • Principal point: Point of intersection of camera axis with 
either picture plane or the camera plate.
 • Focal length: Perpendicular distance from centre of 
camera lens to either to picture plane or camera plate. It 
satisfi es the relation
11 1
fu v
f
uv
uv
==+? =
+
 
 • Nodal point: It is either of two points on the optical 
axis of a lens so located that when all object distances 
are measured from one point, and all images distances 
are measured from other. They satisfy the simple lens 
relation
11 1
fu v
=+
 • Principal plane: It is a plane which contain principal line 
and optical axis.
 ? Photogrammetry
 ? Remote sensing
 ? Geographic information system (GIS)
 ? Global positioning system (GPS)
CHAPTER HIGHLIGHTS
Remote Sensing, 
Photogrammetry GIS and GPS
Part III_Unit 12_Chapter 06.indd   1 5/31/2017   4:55:30 PM
    
Scale of a Vertical Photograph
 • If the elevation of points vary, the scale of the vertical pho-
tograph will vary from point to point on the photograph
Scale
Map distance
Ground distance
== =
-
S
f
Hh
Where
h =  Height of exposure station (or the air plane) above 
the mean seal level.
H = Height of ground above MSL
f = Focal length of camera
 • If A and B are two points on ground having elevations h
a
 
and h
b
 above MSL, the average scale of the line joining 
A and B is
S
f
Hh
h
hh
ab
=
-
+
avg
avg
2
Datum scale S
f
H
=
 • Scale of a photograph S
l
L
h
=
Phote scale
Map scale
Photo distance
Map distance
=
 
Where
l = Distance in photograph
L = Distance on ground
Computation of length of the line between points of 
different elevations from measurement on a vertical 
photograph:
 • If A and B be two ground points having elevations h
a
 and 
h
b
 above MSL and coordinates (X
a
, Y
a
) and (X
b
, Y
b
)
 • Let a and b be the position of corresponding points in 
photograph and (x
a
, y
a
) and (x
b
, y
b
)  be the corresponding 
coordinates, then
x
X
y
Y
f
Hh
x
X
y
Y
f
Hh
X
Hh
f
xX
Hh
f
x
Y
Hh
a
a
a
aa
b
b
b
bb
a
a
ab
b
b
a
==
-
==
-
=
-
·=
-
·
=
-
a a
ab
b
b
f
yY
Hh
f
y ·=
-
·
 
 • Length between AB is given by
LX XY Y
ab ab
=- +- () ()
22
 
Relief Displacement on a 
Vertical Photograph
When the ground is not horizontal the scale of the pho-
tograph varies from point to point. The ground relief is 
shown in perspective on the photograph. Every point 
on the photograph is therefore, displaced from true 
orthography position. This displacement is called relief 
displacement.
Relief displacement, d
Rfh
HH h
=
- ()
d
rh
H
rh
Hh
==
-
0
 1. The relief displacement increases as the distance 
from the principal point increases.
 2. d
H
?
1
Scale of a Tilted Photograph
S
ft mn t
Hh
ft yt
Hh
h
=
-
-
=
-
-
secsin secsin '
 
y' = -x sin ? + y'cos ? + f tan t
Where
? = 180 – s
s = Swing 
t = Tilt
f = Focal length
H = Flying height above datum
h = Height of ground above datum
It can be seen that the tilt and relief displacements tend to 
cancel in the upper part of the photograph while they are 
cumulative in the lower part.
Overlap in the Photographs
Longitudinal overlap = 55 to 65%
Lateral overlap = 15 to 35%
For maximum rectangular area, to be covered by one 
photograph, the rectangle should have the dimension in the 
flight to be one half the dimension normal to the direction 
of flight.
W = 2B; W = 1.22H
W = Width of ground
% overlap ˜ 60% in longitudinal direction.
Number of Photograph 
to Cover a Given Area
Number of photographs required N
A
a
=
Part III_Unit 12_Chapter 06.indd   2 5/31/2017   4:55:32 PM
Page 3


Photogrammetry
Introduction
Photogrammetric surveying or photogrammetry is the sci-
ence and art of obtaining accurate measurements by use of 
photographs, for various purposes such as the construction 
of plainmetric and topographic maps, classifi cation of soils, 
interpretation of geology, acquisition of military intelli-
gence etc. The scale and fl ying height concepts of photo-
grammetry are focused in this chapter.
De? nitions
 • Vertical photograph: It is an aerial photograph made 
with the camera axis (or optical axis) coinciding with the 
direction of gravity. 
 • Tilted photograph: It is an aerial photograph made with 
the camera axis unintentionally tilted from the vertical by 
a small amount (< 3
0
).
 • Oblique photograph: This is also an aerial photography 
taken with camera axis tilted intentionally. If the horizon 
is shown in the photograph, it is said to be high oblique. 
If the apparent horizon is not shown, it is said to be low 
oblique.
 • Terrestrial photogrammetry: Photographs taken from a 
fi xed position on or near the ground.
 • Aerial photogrammetry: Photographs are taken from a 
camera mounted in an aircraft fl ying over the area.
 • Phototheodolite: It is a combination of theodolite and 
terrestrial camera.
 • Camera axis: Line passing through centre of camera lens 
perpendicular both to camera plate (negative) and picture 
plane (photograph).
 • Picture plane: Positive plane, perpendicular to camera 
axis.
 • Principal point: Point of intersection of camera axis with 
either picture plane or the camera plate.
 • Focal length: Perpendicular distance from centre of 
camera lens to either to picture plane or camera plate. It 
satisfi es the relation
11 1
fu v
f
uv
uv
==+? =
+
 
 • Nodal point: It is either of two points on the optical 
axis of a lens so located that when all object distances 
are measured from one point, and all images distances 
are measured from other. They satisfy the simple lens 
relation
11 1
fu v
=+
 • Principal plane: It is a plane which contain principal line 
and optical axis.
 ? Photogrammetry
 ? Remote sensing
 ? Geographic information system (GIS)
 ? Global positioning system (GPS)
CHAPTER HIGHLIGHTS
Remote Sensing, 
Photogrammetry GIS and GPS
Part III_Unit 12_Chapter 06.indd   1 5/31/2017   4:55:30 PM
    
Scale of a Vertical Photograph
 • If the elevation of points vary, the scale of the vertical pho-
tograph will vary from point to point on the photograph
Scale
Map distance
Ground distance
== =
-
S
f
Hh
Where
h =  Height of exposure station (or the air plane) above 
the mean seal level.
H = Height of ground above MSL
f = Focal length of camera
 • If A and B are two points on ground having elevations h
a
 
and h
b
 above MSL, the average scale of the line joining 
A and B is
S
f
Hh
h
hh
ab
=
-
+
avg
avg
2
Datum scale S
f
H
=
 • Scale of a photograph S
l
L
h
=
Phote scale
Map scale
Photo distance
Map distance
=
 
Where
l = Distance in photograph
L = Distance on ground
Computation of length of the line between points of 
different elevations from measurement on a vertical 
photograph:
 • If A and B be two ground points having elevations h
a
 and 
h
b
 above MSL and coordinates (X
a
, Y
a
) and (X
b
, Y
b
)
 • Let a and b be the position of corresponding points in 
photograph and (x
a
, y
a
) and (x
b
, y
b
)  be the corresponding 
coordinates, then
x
X
y
Y
f
Hh
x
X
y
Y
f
Hh
X
Hh
f
xX
Hh
f
x
Y
Hh
a
a
a
aa
b
b
b
bb
a
a
ab
b
b
a
==
-
==
-
=
-
·=
-
·
=
-
a a
ab
b
b
f
yY
Hh
f
y ·=
-
·
 
 • Length between AB is given by
LX XY Y
ab ab
=- +- () ()
22
 
Relief Displacement on a 
Vertical Photograph
When the ground is not horizontal the scale of the pho-
tograph varies from point to point. The ground relief is 
shown in perspective on the photograph. Every point 
on the photograph is therefore, displaced from true 
orthography position. This displacement is called relief 
displacement.
Relief displacement, d
Rfh
HH h
=
- ()
d
rh
H
rh
Hh
==
-
0
 1. The relief displacement increases as the distance 
from the principal point increases.
 2. d
H
?
1
Scale of a Tilted Photograph
S
ft mn t
Hh
ft yt
Hh
h
=
-
-
=
-
-
secsin secsin '
 
y' = -x sin ? + y'cos ? + f tan t
Where
? = 180 – s
s = Swing 
t = Tilt
f = Focal length
H = Flying height above datum
h = Height of ground above datum
It can be seen that the tilt and relief displacements tend to 
cancel in the upper part of the photograph while they are 
cumulative in the lower part.
Overlap in the Photographs
Longitudinal overlap = 55 to 65%
Lateral overlap = 15 to 35%
For maximum rectangular area, to be covered by one 
photograph, the rectangle should have the dimension in the 
flight to be one half the dimension normal to the direction 
of flight.
W = 2B; W = 1.22H
W = Width of ground
% overlap ˜ 60% in longitudinal direction.
Number of Photograph 
to Cover a Given Area
Number of photographs required N
A
a
=
Part III_Unit 12_Chapter 06.indd   2 5/31/2017   4:55:32 PM
      
Where
A = Total area to be photographed
a = Net ground area covered by each photograph
 a = L × W
 L = (1 – P
l
)s · l
 W = (1 – P
w
)s · l
 a = lws
2
(1 – P
l
)(1 – P
w
)
Where
l = Length of photograph in direction of flight 
W = Width of photograph
P
l
, P
W
 = % overlap in longitudinal and lateral directions.
 • If instead of total areal A, the rectangular dimensions L
1
 
× L
2
 (parallel and transverse to flight) are given, then the 
number of photographs required are as follows.
 • Let L
1
, L
2
 = dimension of area parallel and transverse to 
the direction of flight.
N
1
 = Number of photographs in each strip
N
2
 = Number of strips required
Total number of photographs to cover the whole area, N 
= N
1
 × N
2
N
L
Ps l
N
L
Ps l
l
w
1
1
1
2
1
1
1
1
=
-·
+
=
-·
+
()
()
 
Interval Between Exposures
T
L
V
=
× 3600
V = Ground speed of airplane, in km/h
L = Ground distance covered by each photograph in the 
direction of flight 
= (1 – P
l
)s · l … in km 
Elevation of a Point by Photographic 
Measurement
tan
tan
sec
cos
a
ß
a
a
a
a
a
aa
a
a
a
X
f
Y
Oa
y
f
Y
f
=
== =
1
 
If V = Elevation of point A above horizontal plane through 
camera axis. From similar triangle
y
f
V
D
a
a
seca
=
So, V
yD
f
yD
fx
yD
fx
a
a
a
a
==
+
=
+
seca
22 22
X
a
2
+
 
f
2
a
a
 f
x
a
a
D
fseca
a
y
a
a
1
A
1
V
A
So, V
yD
f
yD
fx
==
+
cosa
22
Elevation of point A,
 
h = H
c
 + V + C
Where
H
c
 = Elevation of camera 
V = Elevation of point A
C = Correction for curvature and refraction.
SOLVED EXAMPLES
Example 1
A tower AB, 60 m high, appears in a vertical photograph 
taken at a flight attitude of 2500 m above mean sea level. 
The distance of the image of the top of the tower is 5.32 cm. 
Compute the displacement of the image of the top of the 
tower with respect to the image of its bottom. The elevation 
of the bottom of the tower is 1270 m.
Solution
Let H = Height of lens above the bottom of the tower.
The displacement d of the image of the top with respect to 
the image of the bottom is given by 
d
hr
H
=
h = Height of the tower above its base = 60 m
H = 2500 – 1270 = 1230
d =
×
=
60 532
1230
026
.
.cm.
Remote Sensing
It is the science and art of obtaining information about an 
object, area or phenomenon through the analysis of data 
acquired by a device that is not in contact with the object 
area, or phenomenon under investigation. Remote sensing 
of each resources involves two basic processes:
 1. Data-acquisition process 
 2. Data analysis
Part III_Unit 12_Chapter 06.indd   3 5/31/2017   4:55:33 PM
Page 4


Photogrammetry
Introduction
Photogrammetric surveying or photogrammetry is the sci-
ence and art of obtaining accurate measurements by use of 
photographs, for various purposes such as the construction 
of plainmetric and topographic maps, classifi cation of soils, 
interpretation of geology, acquisition of military intelli-
gence etc. The scale and fl ying height concepts of photo-
grammetry are focused in this chapter.
De? nitions
 • Vertical photograph: It is an aerial photograph made 
with the camera axis (or optical axis) coinciding with the 
direction of gravity. 
 • Tilted photograph: It is an aerial photograph made with 
the camera axis unintentionally tilted from the vertical by 
a small amount (< 3
0
).
 • Oblique photograph: This is also an aerial photography 
taken with camera axis tilted intentionally. If the horizon 
is shown in the photograph, it is said to be high oblique. 
If the apparent horizon is not shown, it is said to be low 
oblique.
 • Terrestrial photogrammetry: Photographs taken from a 
fi xed position on or near the ground.
 • Aerial photogrammetry: Photographs are taken from a 
camera mounted in an aircraft fl ying over the area.
 • Phototheodolite: It is a combination of theodolite and 
terrestrial camera.
 • Camera axis: Line passing through centre of camera lens 
perpendicular both to camera plate (negative) and picture 
plane (photograph).
 • Picture plane: Positive plane, perpendicular to camera 
axis.
 • Principal point: Point of intersection of camera axis with 
either picture plane or the camera plate.
 • Focal length: Perpendicular distance from centre of 
camera lens to either to picture plane or camera plate. It 
satisfi es the relation
11 1
fu v
f
uv
uv
==+? =
+
 
 • Nodal point: It is either of two points on the optical 
axis of a lens so located that when all object distances 
are measured from one point, and all images distances 
are measured from other. They satisfy the simple lens 
relation
11 1
fu v
=+
 • Principal plane: It is a plane which contain principal line 
and optical axis.
 ? Photogrammetry
 ? Remote sensing
 ? Geographic information system (GIS)
 ? Global positioning system (GPS)
CHAPTER HIGHLIGHTS
Remote Sensing, 
Photogrammetry GIS and GPS
Part III_Unit 12_Chapter 06.indd   1 5/31/2017   4:55:30 PM
    
Scale of a Vertical Photograph
 • If the elevation of points vary, the scale of the vertical pho-
tograph will vary from point to point on the photograph
Scale
Map distance
Ground distance
== =
-
S
f
Hh
Where
h =  Height of exposure station (or the air plane) above 
the mean seal level.
H = Height of ground above MSL
f = Focal length of camera
 • If A and B are two points on ground having elevations h
a
 
and h
b
 above MSL, the average scale of the line joining 
A and B is
S
f
Hh
h
hh
ab
=
-
+
avg
avg
2
Datum scale S
f
H
=
 • Scale of a photograph S
l
L
h
=
Phote scale
Map scale
Photo distance
Map distance
=
 
Where
l = Distance in photograph
L = Distance on ground
Computation of length of the line between points of 
different elevations from measurement on a vertical 
photograph:
 • If A and B be two ground points having elevations h
a
 and 
h
b
 above MSL and coordinates (X
a
, Y
a
) and (X
b
, Y
b
)
 • Let a and b be the position of corresponding points in 
photograph and (x
a
, y
a
) and (x
b
, y
b
)  be the corresponding 
coordinates, then
x
X
y
Y
f
Hh
x
X
y
Y
f
Hh
X
Hh
f
xX
Hh
f
x
Y
Hh
a
a
a
aa
b
b
b
bb
a
a
ab
b
b
a
==
-
==
-
=
-
·=
-
·
=
-
a a
ab
b
b
f
yY
Hh
f
y ·=
-
·
 
 • Length between AB is given by
LX XY Y
ab ab
=- +- () ()
22
 
Relief Displacement on a 
Vertical Photograph
When the ground is not horizontal the scale of the pho-
tograph varies from point to point. The ground relief is 
shown in perspective on the photograph. Every point 
on the photograph is therefore, displaced from true 
orthography position. This displacement is called relief 
displacement.
Relief displacement, d
Rfh
HH h
=
- ()
d
rh
H
rh
Hh
==
-
0
 1. The relief displacement increases as the distance 
from the principal point increases.
 2. d
H
?
1
Scale of a Tilted Photograph
S
ft mn t
Hh
ft yt
Hh
h
=
-
-
=
-
-
secsin secsin '
 
y' = -x sin ? + y'cos ? + f tan t
Where
? = 180 – s
s = Swing 
t = Tilt
f = Focal length
H = Flying height above datum
h = Height of ground above datum
It can be seen that the tilt and relief displacements tend to 
cancel in the upper part of the photograph while they are 
cumulative in the lower part.
Overlap in the Photographs
Longitudinal overlap = 55 to 65%
Lateral overlap = 15 to 35%
For maximum rectangular area, to be covered by one 
photograph, the rectangle should have the dimension in the 
flight to be one half the dimension normal to the direction 
of flight.
W = 2B; W = 1.22H
W = Width of ground
% overlap ˜ 60% in longitudinal direction.
Number of Photograph 
to Cover a Given Area
Number of photographs required N
A
a
=
Part III_Unit 12_Chapter 06.indd   2 5/31/2017   4:55:32 PM
      
Where
A = Total area to be photographed
a = Net ground area covered by each photograph
 a = L × W
 L = (1 – P
l
)s · l
 W = (1 – P
w
)s · l
 a = lws
2
(1 – P
l
)(1 – P
w
)
Where
l = Length of photograph in direction of flight 
W = Width of photograph
P
l
, P
W
 = % overlap in longitudinal and lateral directions.
 • If instead of total areal A, the rectangular dimensions L
1
 
× L
2
 (parallel and transverse to flight) are given, then the 
number of photographs required are as follows.
 • Let L
1
, L
2
 = dimension of area parallel and transverse to 
the direction of flight.
N
1
 = Number of photographs in each strip
N
2
 = Number of strips required
Total number of photographs to cover the whole area, N 
= N
1
 × N
2
N
L
Ps l
N
L
Ps l
l
w
1
1
1
2
1
1
1
1
=
-·
+
=
-·
+
()
()
 
Interval Between Exposures
T
L
V
=
× 3600
V = Ground speed of airplane, in km/h
L = Ground distance covered by each photograph in the 
direction of flight 
= (1 – P
l
)s · l … in km 
Elevation of a Point by Photographic 
Measurement
tan
tan
sec
cos
a
ß
a
a
a
a
a
aa
a
a
a
X
f
Y
Oa
y
f
Y
f
=
== =
1
 
If V = Elevation of point A above horizontal plane through 
camera axis. From similar triangle
y
f
V
D
a
a
seca
=
So, V
yD
f
yD
fx
yD
fx
a
a
a
a
==
+
=
+
seca
22 22
X
a
2
+
 
f
2
a
a
 f
x
a
a
D
fseca
a
y
a
a
1
A
1
V
A
So, V
yD
f
yD
fx
==
+
cosa
22
Elevation of point A,
 
h = H
c
 + V + C
Where
H
c
 = Elevation of camera 
V = Elevation of point A
C = Correction for curvature and refraction.
SOLVED EXAMPLES
Example 1
A tower AB, 60 m high, appears in a vertical photograph 
taken at a flight attitude of 2500 m above mean sea level. 
The distance of the image of the top of the tower is 5.32 cm. 
Compute the displacement of the image of the top of the 
tower with respect to the image of its bottom. The elevation 
of the bottom of the tower is 1270 m.
Solution
Let H = Height of lens above the bottom of the tower.
The displacement d of the image of the top with respect to 
the image of the bottom is given by 
d
hr
H
=
h = Height of the tower above its base = 60 m
H = 2500 – 1270 = 1230
d =
×
=
60 532
1230
026
.
.cm.
Remote Sensing
It is the science and art of obtaining information about an 
object, area or phenomenon through the analysis of data 
acquired by a device that is not in contact with the object 
area, or phenomenon under investigation. Remote sensing 
of each resources involves two basic processes:
 1. Data-acquisition process 
 2. Data analysis
Part III_Unit 12_Chapter 06.indd   3 5/31/2017   4:55:33 PM
    
Observation Platforms
Two types of platforms have been in use in remote sensing. 
 1. Air borne platforms
 2. Space based platforms
Air Borne Platforms
Air borne remote sensing was the well-known method used 
in initial years of development of remote sensing. Air crafts 
were mostly used as RS platforms for obtaining photo-
graphs. Aircraft carrying RS equipment should have maxi-
mum stability, free from vibrations and fly with uniform 
speed. Aircraft operations are very expensive for periodi-
cal monitoring of constantly changing phenomena like crop 
growth, vegetation cover, etc. Aircraft based platform can-
not provide cost and time effective solutions.
Space Based Platforms
Space borne RS platforms, offer several advantages over 
airborne platforms.
It provides synoptic view (i.e., large area in a single 
image), systematic and repetitive coverage. 
Satellite is a platform that carries the sensor and other 
payloads required in RS operation.
Space borne platforms are broadly divided into two 
classes.
 1. Low altitude near polar orbiting satellites: These 
are the RS satellites which revolve around earth in a 
sun synchronous orbit defined by its fixed inclination 
angle from the earths NS axis.
 2. High attitude Geo-stationary satellites: These 
are mostly communication/meteorological satellites 
which are stationary in reference to the earth. Its 
velocity is equal to the velocity with which earth 
rotates about its axis. Such satellites always cover the 
fixed area over earth surface and their attitude is about 
36,000 km.
Sensors
RS sensors are designed to record radiations in one or 
more parts of the EM spectrum.
Sensors used in Indian RS Satellites (IRS)
 1. Linear imaging and self scanning sensor (LISS I)
 2. Linear imaging and self scanning sensor (LISS II)
 3. Linear imaging and self scanning sensor (LISS III)
 4. Panchromatic sensor (PAN)
 5. Wide field sensor (WiFS)
 6. Modular opto-electronic scanner (MOS)
 7. Ocean colour monitor (OCM)
 8. Multi-scanning microwave radiometer (MSMR)
Generally sensors are of two types:
 1. Active sensors: These utilizes the man-made sources 
and detect the electro magnetic radiation of a specific 
wavelengths to illuminate the earth’s surface are 
called active sensors.
 2. Passive sensors: Sensors that sense natural 
radiations, either reflected or emitted from the earth, 
are called passive sensors.
Visual Image Interpretation
The data interpretation aspects of RS can involve analysis 
of photographs (images) and/or digital data. This can be 
performed by visual interpretation or with the help of com-
puter assisted analysis techniques. 
Photo interpretation means identifying and recognizing 
objects in the aerial photograph and then judging their char-
acteristics and significance in the photograph.
The following characteristics of the photo images are 
studied:
 1. Shape: This relates to general form, configuration or 
outline of an object. This is an important factor for 
recognizing objects form their photographic images.
 2. Size: Objects can be misinterpreted, if the sizes are 
not properly evaluated.
  Example: A canal may be interpreted as a road side 
drain.
 3. Pattern: Pattern means spatial arrangement of the 
objects photographed.
  Example: Building, roads, etc., have a particular 
pattern which can easily be recognized.
 4. Shadow: The outline of a shadow gives the profile of 
an object, which aids in interpretation.
 5. Texture: Texture is the frequency of the change in 
tone in photographic image.
  Example: Large leaf tree species can be distinguished 
from small leaf species on the basis of their coarser 
texture.
 6. Site: The location of an object in relation to its 
surroundings is very helpful in identification. 
  Example: A building in a forest might not be 
identified, whereas it can be easily identified in 
residential areas.
Applications of Remote Sensing
 1. Agriculture: Crop growth profile, crop yield 
modeling, crop violations.
 2. Forestry: Forest fire, deforestation, forest stock 
mapping, wild life habitat assessment.
 3. Land use/land cover analysis: Soil categorization, 
mapping land use/cover, change detection, identifying 
degraded lands/erosion prone areas.
Part III_Unit 12_Chapter 06.indd   4 5/31/2017   4:55:33 PM
Page 5


Photogrammetry
Introduction
Photogrammetric surveying or photogrammetry is the sci-
ence and art of obtaining accurate measurements by use of 
photographs, for various purposes such as the construction 
of plainmetric and topographic maps, classifi cation of soils, 
interpretation of geology, acquisition of military intelli-
gence etc. The scale and fl ying height concepts of photo-
grammetry are focused in this chapter.
De? nitions
 • Vertical photograph: It is an aerial photograph made 
with the camera axis (or optical axis) coinciding with the 
direction of gravity. 
 • Tilted photograph: It is an aerial photograph made with 
the camera axis unintentionally tilted from the vertical by 
a small amount (< 3
0
).
 • Oblique photograph: This is also an aerial photography 
taken with camera axis tilted intentionally. If the horizon 
is shown in the photograph, it is said to be high oblique. 
If the apparent horizon is not shown, it is said to be low 
oblique.
 • Terrestrial photogrammetry: Photographs taken from a 
fi xed position on or near the ground.
 • Aerial photogrammetry: Photographs are taken from a 
camera mounted in an aircraft fl ying over the area.
 • Phototheodolite: It is a combination of theodolite and 
terrestrial camera.
 • Camera axis: Line passing through centre of camera lens 
perpendicular both to camera plate (negative) and picture 
plane (photograph).
 • Picture plane: Positive plane, perpendicular to camera 
axis.
 • Principal point: Point of intersection of camera axis with 
either picture plane or the camera plate.
 • Focal length: Perpendicular distance from centre of 
camera lens to either to picture plane or camera plate. It 
satisfi es the relation
11 1
fu v
f
uv
uv
==+? =
+
 
 • Nodal point: It is either of two points on the optical 
axis of a lens so located that when all object distances 
are measured from one point, and all images distances 
are measured from other. They satisfy the simple lens 
relation
11 1
fu v
=+
 • Principal plane: It is a plane which contain principal line 
and optical axis.
 ? Photogrammetry
 ? Remote sensing
 ? Geographic information system (GIS)
 ? Global positioning system (GPS)
CHAPTER HIGHLIGHTS
Remote Sensing, 
Photogrammetry GIS and GPS
Part III_Unit 12_Chapter 06.indd   1 5/31/2017   4:55:30 PM
    
Scale of a Vertical Photograph
 • If the elevation of points vary, the scale of the vertical pho-
tograph will vary from point to point on the photograph
Scale
Map distance
Ground distance
== =
-
S
f
Hh
Where
h =  Height of exposure station (or the air plane) above 
the mean seal level.
H = Height of ground above MSL
f = Focal length of camera
 • If A and B are two points on ground having elevations h
a
 
and h
b
 above MSL, the average scale of the line joining 
A and B is
S
f
Hh
h
hh
ab
=
-
+
avg
avg
2
Datum scale S
f
H
=
 • Scale of a photograph S
l
L
h
=
Phote scale
Map scale
Photo distance
Map distance
=
 
Where
l = Distance in photograph
L = Distance on ground
Computation of length of the line between points of 
different elevations from measurement on a vertical 
photograph:
 • If A and B be two ground points having elevations h
a
 and 
h
b
 above MSL and coordinates (X
a
, Y
a
) and (X
b
, Y
b
)
 • Let a and b be the position of corresponding points in 
photograph and (x
a
, y
a
) and (x
b
, y
b
)  be the corresponding 
coordinates, then
x
X
y
Y
f
Hh
x
X
y
Y
f
Hh
X
Hh
f
xX
Hh
f
x
Y
Hh
a
a
a
aa
b
b
b
bb
a
a
ab
b
b
a
==
-
==
-
=
-
·=
-
·
=
-
a a
ab
b
b
f
yY
Hh
f
y ·=
-
·
 
 • Length between AB is given by
LX XY Y
ab ab
=- +- () ()
22
 
Relief Displacement on a 
Vertical Photograph
When the ground is not horizontal the scale of the pho-
tograph varies from point to point. The ground relief is 
shown in perspective on the photograph. Every point 
on the photograph is therefore, displaced from true 
orthography position. This displacement is called relief 
displacement.
Relief displacement, d
Rfh
HH h
=
- ()
d
rh
H
rh
Hh
==
-
0
 1. The relief displacement increases as the distance 
from the principal point increases.
 2. d
H
?
1
Scale of a Tilted Photograph
S
ft mn t
Hh
ft yt
Hh
h
=
-
-
=
-
-
secsin secsin '
 
y' = -x sin ? + y'cos ? + f tan t
Where
? = 180 – s
s = Swing 
t = Tilt
f = Focal length
H = Flying height above datum
h = Height of ground above datum
It can be seen that the tilt and relief displacements tend to 
cancel in the upper part of the photograph while they are 
cumulative in the lower part.
Overlap in the Photographs
Longitudinal overlap = 55 to 65%
Lateral overlap = 15 to 35%
For maximum rectangular area, to be covered by one 
photograph, the rectangle should have the dimension in the 
flight to be one half the dimension normal to the direction 
of flight.
W = 2B; W = 1.22H
W = Width of ground
% overlap ˜ 60% in longitudinal direction.
Number of Photograph 
to Cover a Given Area
Number of photographs required N
A
a
=
Part III_Unit 12_Chapter 06.indd   2 5/31/2017   4:55:32 PM
      
Where
A = Total area to be photographed
a = Net ground area covered by each photograph
 a = L × W
 L = (1 – P
l
)s · l
 W = (1 – P
w
)s · l
 a = lws
2
(1 – P
l
)(1 – P
w
)
Where
l = Length of photograph in direction of flight 
W = Width of photograph
P
l
, P
W
 = % overlap in longitudinal and lateral directions.
 • If instead of total areal A, the rectangular dimensions L
1
 
× L
2
 (parallel and transverse to flight) are given, then the 
number of photographs required are as follows.
 • Let L
1
, L
2
 = dimension of area parallel and transverse to 
the direction of flight.
N
1
 = Number of photographs in each strip
N
2
 = Number of strips required
Total number of photographs to cover the whole area, N 
= N
1
 × N
2
N
L
Ps l
N
L
Ps l
l
w
1
1
1
2
1
1
1
1
=
-·
+
=
-·
+
()
()
 
Interval Between Exposures
T
L
V
=
× 3600
V = Ground speed of airplane, in km/h
L = Ground distance covered by each photograph in the 
direction of flight 
= (1 – P
l
)s · l … in km 
Elevation of a Point by Photographic 
Measurement
tan
tan
sec
cos
a
ß
a
a
a
a
a
aa
a
a
a
X
f
Y
Oa
y
f
Y
f
=
== =
1
 
If V = Elevation of point A above horizontal plane through 
camera axis. From similar triangle
y
f
V
D
a
a
seca
=
So, V
yD
f
yD
fx
yD
fx
a
a
a
a
==
+
=
+
seca
22 22
X
a
2
+
 
f
2
a
a
 f
x
a
a
D
fseca
a
y
a
a
1
A
1
V
A
So, V
yD
f
yD
fx
==
+
cosa
22
Elevation of point A,
 
h = H
c
 + V + C
Where
H
c
 = Elevation of camera 
V = Elevation of point A
C = Correction for curvature and refraction.
SOLVED EXAMPLES
Example 1
A tower AB, 60 m high, appears in a vertical photograph 
taken at a flight attitude of 2500 m above mean sea level. 
The distance of the image of the top of the tower is 5.32 cm. 
Compute the displacement of the image of the top of the 
tower with respect to the image of its bottom. The elevation 
of the bottom of the tower is 1270 m.
Solution
Let H = Height of lens above the bottom of the tower.
The displacement d of the image of the top with respect to 
the image of the bottom is given by 
d
hr
H
=
h = Height of the tower above its base = 60 m
H = 2500 – 1270 = 1230
d =
×
=
60 532
1230
026
.
.cm.
Remote Sensing
It is the science and art of obtaining information about an 
object, area or phenomenon through the analysis of data 
acquired by a device that is not in contact with the object 
area, or phenomenon under investigation. Remote sensing 
of each resources involves two basic processes:
 1. Data-acquisition process 
 2. Data analysis
Part III_Unit 12_Chapter 06.indd   3 5/31/2017   4:55:33 PM
    
Observation Platforms
Two types of platforms have been in use in remote sensing. 
 1. Air borne platforms
 2. Space based platforms
Air Borne Platforms
Air borne remote sensing was the well-known method used 
in initial years of development of remote sensing. Air crafts 
were mostly used as RS platforms for obtaining photo-
graphs. Aircraft carrying RS equipment should have maxi-
mum stability, free from vibrations and fly with uniform 
speed. Aircraft operations are very expensive for periodi-
cal monitoring of constantly changing phenomena like crop 
growth, vegetation cover, etc. Aircraft based platform can-
not provide cost and time effective solutions.
Space Based Platforms
Space borne RS platforms, offer several advantages over 
airborne platforms.
It provides synoptic view (i.e., large area in a single 
image), systematic and repetitive coverage. 
Satellite is a platform that carries the sensor and other 
payloads required in RS operation.
Space borne platforms are broadly divided into two 
classes.
 1. Low altitude near polar orbiting satellites: These 
are the RS satellites which revolve around earth in a 
sun synchronous orbit defined by its fixed inclination 
angle from the earths NS axis.
 2. High attitude Geo-stationary satellites: These 
are mostly communication/meteorological satellites 
which are stationary in reference to the earth. Its 
velocity is equal to the velocity with which earth 
rotates about its axis. Such satellites always cover the 
fixed area over earth surface and their attitude is about 
36,000 km.
Sensors
RS sensors are designed to record radiations in one or 
more parts of the EM spectrum.
Sensors used in Indian RS Satellites (IRS)
 1. Linear imaging and self scanning sensor (LISS I)
 2. Linear imaging and self scanning sensor (LISS II)
 3. Linear imaging and self scanning sensor (LISS III)
 4. Panchromatic sensor (PAN)
 5. Wide field sensor (WiFS)
 6. Modular opto-electronic scanner (MOS)
 7. Ocean colour monitor (OCM)
 8. Multi-scanning microwave radiometer (MSMR)
Generally sensors are of two types:
 1. Active sensors: These utilizes the man-made sources 
and detect the electro magnetic radiation of a specific 
wavelengths to illuminate the earth’s surface are 
called active sensors.
 2. Passive sensors: Sensors that sense natural 
radiations, either reflected or emitted from the earth, 
are called passive sensors.
Visual Image Interpretation
The data interpretation aspects of RS can involve analysis 
of photographs (images) and/or digital data. This can be 
performed by visual interpretation or with the help of com-
puter assisted analysis techniques. 
Photo interpretation means identifying and recognizing 
objects in the aerial photograph and then judging their char-
acteristics and significance in the photograph.
The following characteristics of the photo images are 
studied:
 1. Shape: This relates to general form, configuration or 
outline of an object. This is an important factor for 
recognizing objects form their photographic images.
 2. Size: Objects can be misinterpreted, if the sizes are 
not properly evaluated.
  Example: A canal may be interpreted as a road side 
drain.
 3. Pattern: Pattern means spatial arrangement of the 
objects photographed.
  Example: Building, roads, etc., have a particular 
pattern which can easily be recognized.
 4. Shadow: The outline of a shadow gives the profile of 
an object, which aids in interpretation.
 5. Texture: Texture is the frequency of the change in 
tone in photographic image.
  Example: Large leaf tree species can be distinguished 
from small leaf species on the basis of their coarser 
texture.
 6. Site: The location of an object in relation to its 
surroundings is very helpful in identification. 
  Example: A building in a forest might not be 
identified, whereas it can be easily identified in 
residential areas.
Applications of Remote Sensing
 1. Agriculture: Crop growth profile, crop yield 
modeling, crop violations.
 2. Forestry: Forest fire, deforestation, forest stock 
mapping, wild life habitat assessment.
 3. Land use/land cover analysis: Soil categorization, 
mapping land use/cover, change detection, identifying 
degraded lands/erosion prone areas.
Part III_Unit 12_Chapter 06.indd   4 5/31/2017   4:55:33 PM
      
 4. Geology: Drainage analysis, coal fire mapping, 
mineral exploration, oil field detection.
 5. Environmental hazards
 6. Water resources: Glacier inventory, surface water 
bodies monitoring and estimation of their spatial 
extent.
Geographic Information 
System (GIS)
 • GIS is an information technology which stores, analyses 
and displays both spatial and non-spatial data.
 • GIS is capable of acquiring spatially indexed data from a 
variety of sources, changing the data into useful formats, 
storing the data, retrieving and manipulating the data for 
analysis and then generating the output required by the 
user.  The acquired specified indexed data are known as 
layers. Each layer represents a thematic approach to a par-
ticular purpose.
(a) Themes (b) Floor wise information
(c) Time periods
2014
2015
Drinage system
Land use pattern
Road network
In water distribution
network
Topgraphy
Top ?oor
2013
Second ?oor
First ?oor
Ground ?oor
Foundation
A layered database concept
The main advantage of GIS is rapid analysis and display 
of data with flexibility which is not possible using manual 
methods.
Data for GIS
The basic forms of the data for GIS:
 1. Spatial data: Data that provide locations and shapes 
of features in a map.
 2. Tabular data: Data that are collected or complied for 
a given area, GIS links this to features in a map.
 3. Image data: Aerial photographs and products, 
satellite images, scanned data (photographic prints 
converted to digital format).
Representation of Features
 1. Point data 
 2. Line and string data
 3. Areal data
 4. Pixels 
 5. Grid cells
Data Structure for GIS
Data are frequently derived from a ‘conventional’ (non-
digital) map or image. It is necessary to convert them into 
digital form suitable for use by a GIS.
The simple spatial objects are coded in two different for -
mats–vector and raster–for storing and manipulating these 
in a GIS. These data structures are also called data models 
or data formats.
Vector Data Structure
Vector data depicts the real world by means of discrete 
points, lines and polygons and is sorted as a collection of 
x, y coordinates.
Part III_Unit 12_Chapter 06.indd   5 5/31/2017   4:55:33 PM