CE203 -Photogrammetry & GPS.ppt
- 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.
- 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.
- 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 ?
- 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