Photogrammetry & GPS

1. Assistant Professor
Dr Abdul Hannan Qureshi
BSc(Civil-Honor), MSc(CE&M), PhD (Civil), P.E. (CM)
Email: ahananq@gmail.com
LECTURE #
Advanced
Engineering
Surveying

2. PHOTOGRAMETTERY
ADVANCED ENGINEERING SURVEY (CE-2203)

6. Analog photogrammetry is performed visually by
humans and is used when data are in a hard-copy
format.
Digital or analytical photogrammetry is performed
with the aid of a computer using digitized aerial
photography.

17. Each vertical aerial photograph overlaps the next photograph in the flight-line
by approximately 60% which refers to as stereoscopic overlap. This overlap is
very important because it provides at least two and sometimes three photographic
views of each object on the ground along the flight-line.

25. More than 1000ft

26. 300 ft

27. 200 ft

28. 120 ft

29. 93 ft

35. Drones and airplanes both can be used for aerial
photogrammetry now a days, whichever is approachable.

37. https://youtu.be/EvA7PdhWWTg
APPLICATIONS

38. Stereoscopy:
In aerial photography, when two photographs overlap or the same
ground area is photographed from two separate position forms a
stereo-pair, used for three dimension viewing. Thus obtained a pair
of stereoscopic photographs or images, can be viewed
stereoscopically.
Stereoscopic plotting instruments (commonly called stereo plotters
or simply "plotters") are instruments designed to provide rigorously
accurate solutions for object point positions from their corresponding
image positions on overlapping pairs of photos.

43. GLOBAL POSITIONING
SYSTEM (GPS)

44. What is GPS?
GPS, which stands for Global Positioning System. It is
one of the satellite systems currently in use. It is able to
show you your exact position on the surface of earth
anytime, in any weather, anywhere.

45. GPS Need
GPS is a solution for one of man's longest problems.
Where on earth am I ?.
One can say, “you can easily locate yourself by
looking at objects that surround you and position
yourself relative to them”.
But what if you have no objects around you ?
What if you are
In the middle of a desert
or
 In the middle of an ocean ?
Then GPS comes to your rescue.

46. Origin of GPS
First idea came after the launch of Russian
Satellite Sputnik in 1957
– Two Scientists at Johns Hopkins University (JHU)
realized they could pinpoint the location of the
satellite by analyzing the radio signals.
– Frank McClure, then went a step further by
suggesting that if the satellite's position were known
and predictable, then we can also locate a receiver
on Earth; in other words, one could navigate by
satellite.

47. Satellites
There are quite a number of
satellites out there in space.
They are used for a wide
range of purposes e.g:
1. Communication satellite
2. Imaging satellites
3. Global Navigation
Satellite Systems etc.
How ever at present we
are referring to the third
category

48. Basically there are three segments of GPS
The Space Segment . Satellites orbiting the earth.
The Control Segment . Stations positioned on the
earth's equator to control the satellites.
The User Segment . Anybody that receives and uses the
GPS signal.
GPS Segments

49. Space Segment
The GPS Operational
Constellation
consists of 24
satellites that orbit
the Earth in very
precise orbits twice a
day. GPS satellites
emit continuous
navigation signals.

50. The space segment
is so designed that
there will be a
minimum of 4
satellites visible
above a 15° cut-off
angle at any point of
the earth surface at
any one time.
Space Segment

51. Control Segment
The Control Segment consists of one master control station, monitor
stations and 4 ground antennas distributed amongst 5 locations roughly
on the earth's equator. The Control Segment tracks the GPS satellites,
updates their orbiting position and calibrates and synchronizes their
clocks.
A further important function is to determine the orbit of each satellite and
predict it's path for the following 24 hours.

52. User Segment
The User Segment
comprises of anyone
using a GPS receiver to
receive the GPS signal and
determine their position
and or time. Typical
applications within the
user segment are land
navigation for hikers,
vehicle location,
surveying, marine
navigation, aerial
navigation, machine
control etc.

53. Receivers and Satellites
GPS units are made
to communicate with
GPS satellites
(which have a much
better view of the
Earth) to find out
exactly where they
are on the global
scale of things.

54. GPS Signals
Each GPS satellite
transmits data that
indicates its location
and the current time.
All GPS satellites
synchronize
operations so that
these repeating
signals are
transmitted at the
same instant.
Physically the signal is
just a complicated
digital code, or in other
words, a complicated
sequence of “on” and
“off” pulses.

55. How GPS works

56. GPS – Concept
 User measures distance to four
satellites
 Satellites transmit their
positions in orbit
 User solves for position (X,Y,Z
or φ,λ,h) and clock error ∆t
Working of GPS is based on
the 'trilateration'
mathematical principle. The
position is determined from the
distance measurements to
satellites. From the figure, the
four satellites are used to
determine the position of the
receiver on the earth.

57. Time Difference
The GPS receiver
compares the time a
signal was transmitted
by a satellite with the
time it was received.
The time difference
tells the GPS receiver
how far away the
satellite is.

58. Calculating Distance
Velocity x Time = Distance
Radio waves travel at the speed of light, roughly 186,000
miles per second (mps)
If it took 0.06 seconds to receive a signal
transmitted by a satellite floating directly
overhead, use this formula to find your distance
from the satellite.
186,000 mps x 0.06 seconds = 11,160 miles

59. METHODS
There are several different methods for
obtaining a position using GPS. The method
used depends on the accuracy required by the
user and the type of GPS receiver available.
Broadly speaking, the techniques can be
broken down into three basic classes:
1. Autonomous Navigation
2. Differential Post Processing
3. Differential Real Time

60. METHODS
• Autonomous
Navigation
using a single stand-
alone receiver. Used by
hikers, ships that are far
out at sea and the
military. Position
Accuracy is better than
100m for civilian users
and about 20m for
military users.

61. Differential Correction
Differential correction is
a technique that greatly
increases the accuracy
of the collected GPS
data. It involves using a
receiver at a known
location - the "base
station“- and comparing
that data with GPS
positions collected from
unknown locations with
"roving receivers."

62.  It is possible to determine the
position of Rover ‘B’ in relation to
Reference ‘A’ provided
 Coordinates of ‘A’ are known
 Simultaneous GPS Observations
 Differential Positioning
 eliminates errors in the
sat. and receiver clocks
 minimizes atmospheric
delays
 Accuracy 5 mm - 5 m
B
A
Differential GPS
?

63. Postprocessing / Real-time

64. SOURCES OF ERROR

65. Line of Sight Transmissions
Line of sight is the
ability to draw a
straight line between
two objects without any
other objects getting in
the way. GPS
transmission are line-
of-sight transmissions.
Obstructions such as trees, buildings, or natural
formations may prevent clear line of sight.

66. Light Refraction
Sometimes the GPS
signal from the
satellite doesn’t
follow a straight line.
Refraction is the
bending of light as
it travels through
one media to
another.

67. Signal Refraction
Signals from satellites can be like light.
When they hit some interference (air patterns
in the atmosphere, uneven geography, etc.)
they sometimes bend a little.

68. Signal Interference
Sometimes the
signals bounce off
things before they
hit the receivers.

69. Satellite Distribution
When the satellites are all in the same part
of the sky, readings will be less accurate.

70. PDOP
All of this
combines to make
the signal less
accurate, and
gives it what we
call a high “PDOP.”
PDOP = Positional Dilution of Precision
11,000 miles
11,000 miles
11,000 miles
11,000 miles
•A PDOP of <4 is excellent
•A PDOP of 4-8 is good
•A PDOP of >8 is poor

71. • Cruise Missiles, Artillery, bombs, etc.
• Defense
• Submarine Navigation
• Combating Terrorism
Military GPS Applications