1. GPS, CONCPTS ,PRNCIPELS &APPLICATIONS
14/04/2019
GPS, CONCPTS ,PRNCIPELS &APPLICATIONS
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Introduction :-
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense.
GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use.
GPS works in any weather conditions, anywhere in the world, 24 hours a day.
There are no subscription fees or setup charges to use GPS.
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The system's positioning and timing data are used for a variety of applications, including air, land and sea navigation, vehicle and vessel tracking, surveying and mapping ,asset and natural Resource management. GPS is the shortened form of NAVSTAR GPS. This is an acronym for Navigation system with Time and Ranging.
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The GPS SYS is composed of a constellation of satellites orbiting approximately
20,000 km (about 12,500 miles) above the Earth The full constellation is defined as satellites.
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The satellites are arrayed in 6 separate orbits, each inclined about 55° with respect to the equator. The orbit is traversed in about 12 hours.
With a full constellation, receivers located on most spots on the Earth can see at least 6 satellites, and sometimes as many as 12 of the satellites at any one time.
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GPS receivers use triangulation to calculate the user's exact location
Precise microwave signals are transmitted from the satellites, allowing a GPS receiver to determine its location, speed and direction.
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Competitors of GPS
GLONASS
- Russian Federation’s satellite navigation system
Galileo
-European Union and the European Space Agency
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The receiver can compute its position using trilateration. Three spheres intersect at a point, there are 3 distances or ranges to resolve, latitude, longitude and height.
tracking four satellites is required in order to correct the receiver's clock error. Here there are four ranges to resolve, latitude, longitude, height and time.
Using just the receiver, (NAVIGATOR)accuracies are about +/- 10metres
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14. Three Segments of the GPS
Space Segment
User Segment
Three Segments of the Global Positioning System
The Global Positioning System is comprised of three segments: the Control Segment, Space Segment and User Segment.
Control Segment
Ground Antennas
Master Station
Monitor Stations

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Segments of GPS System
This system consists of three segments:-
the space segment.
the control segment
and the user segment
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space segment
1- The GPS space segment consists of a constellation of satellites transmitting radio signals to users The Air Force manages the constellation to ensure the availability of at least GPS satellites.
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THE CONTROL SEGMENT
This part consists of 5 worldwide base-stations that monitor the satellites to track their exact position in space, and to make sure that they are operating correctly. The stations constantly monitor the orbits of the satellites and use very precise radar to check altitude, position and speed.
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THE USER SEGMENT
Consists of the GPS Receiver equipment's which receives the signals from the GPS satellites and uses the transmitted information to calculate the user location.
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21. single point positioning
In single point positioning coordinates of a receiver at an "unknown" point are sought with respect to the earth's reference frame by using the "known" positions of the GPS satellites being tracked.
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22. Point positioning Fig. 1:Point Positioning of GPS receiver In this figure, s1, s2, s3 and s4 represent four different satellites (least required) being tracked. The positions of these satellites are referenced to the centre of the earth in the X, Y, Z coordinate frame. The coordinates for s1 are shown as (xs1, ys1, zs1). The coordinates of r, the unknown point, as referenced to the centre of the earth, are assumed to be (xr, yr, zr). The observed code, Prs1, relates the known coordinates of satellite 1 with the unknown coordinates of the receiver using the equation for a line in three-dimensional space. That is, Prs1 = [(Xs1 - Xr)2 + (Ys1 - Yr)2 + (Zs1 - Zr)2] + error Thus, from four satellites, four distance equation can be formed leading to computation of the four unknowns (xr, yr, zr and clock bias) can be computed.

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Relative positioning
The concept of relative positioning is Instead of determining the position of one point on the earth with respect to the satellites (as done in single point positioning), the position of one point on the earth is determined with respect to another "known" point.
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differential positioning (DGPS)
The accuracy can be improved by using two or more receivers which will give ‘differential’ position (DGPS). It is possible to know the position of B in relation to A when the co-ordinates of A are known and the satellites are tracked simultaneously In this situation, (A) would be called a reference station, or base station and( B) would be called a Rover.
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GPS TECHNIQES
Static Positioning :-
- it used when we want to establish control points from known points.
- This method provides the highest accuracy and requires long observation times.
- This method requires post processing software
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* Time in unknown point =10mint +2xdist (km)
accuracy : mm X dist (Km) Hz mm x dis(Km) V
Example for base line length 10km :-
Time = x 10km = 30 mint.
Accuracy = 3mm x10 = 8mm Hz
5mm x10 = 10mm v
BASE (known point)
Unknown point
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27. (RTK( REAL TIME KINEMATIC
RTK GPS survey consist of a data transfer link and at least one GPS receiver over a known point usually a Control Survey Marker which remains stationary and a rover which moves from point to point
In a RTK survey shots are taken from a fixed base station to a rover station, which then transfers the corrections to the rover.
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28. (RTK( REAL TIME KINEMATIC
Occupation times for the rover are generally a few seconds to a few minutes
Effective for areas with a clear view of the horizon
No need for post processing software .
BASE
ROVER
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GPS Coordinate System
GPS measurements are referenced to the 1984 World Geodetic System reference ellipsoid, known as WGS84.
It is better to display and store results in terms of a local coordinate system. Before you start a survey, choose a coordinate system. Depending on the requirements of the survey, you can choose to give the results in the national coordinate system, a local coordinate grid system, or as local geodetic coordinates.
When you have chosen a coordinate system, search your survey archives for any horizontal and vertical control points in that coordinate system that are in the area to be surveyed. You can use these to calibrate a GPS survey.
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30. Local Coordinate Systems
A local coordinate system simply transforms measurements from a curved surface (the earth) onto a flat surface (a map or plan). Four important elements constitute a local coordinate system:
local datum
datum transformation
map projection
calibration (horizontal and vertical adjustments)
When you survey using GPS, consider each of these.
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31. Earth Ellipsoid
An Earth ellipsoid is a mathematical figure approximating the shape of the Earth, used as a reference frame for computations in geodesy, astronomy and the geosciences. Various different ellipsoids have been used as approximations.

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Using a Geoid Model
The geoid is a surface of constant gravitational potential that approximates mean sea level.(assume if the sea covered the earth)
it is used with the GPS ellipsoid height observations to provide
an estimate of elevation.
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33. Ellipsoid Scale Factor
This scale factor accounts for the height of the
ground above the reference surface (the ellipsoid). This scale factor is
defined geometrically: Consider the following diagram:
Dist ground/(R+h) = dist elip/R
Dist elip/dist ground = R/(R+h)
kelip = R/ (R+h)
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Applications of GPS
Civil Engineering
• Civil engineering firms utilize GPS systems for
road construction projects, earth moving projects etc…..
• Some earth moving projects can involve real-time
differential data collection and display that links
with the operator in the cab, allowing the person
to determine if the correct grade has been
reach
• The same technology can also be utilized to
properly place building foundations and other
structural features
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• Other engineering applications include the analysis of structural deformation for various features
– Bridges
– TV towers
– Dams
• GPS can also be utilized to analyze land subsidence caused by oil or groundwater extraction or mining
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36. Example for the application of GPS in civil engineering
In road construction and Earth moving, GPS, combined with wireless communication and computer systems, is installed onboard the Earthmoving machine. Designed surface information, in a digital format, is uploaded into the system. With the help of the computer display and the real-time GPS position information, the operator can view whether the correct grade has been reached. In situations in which millimeter-level elevation is needed, GPS can be integrated with rotated beam lasers
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37. Road construction with GPS
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39. Mining
• Surveys and drill patterns associated with mining were often completed using conventional methods • Stakes marking locations and transects would get misplaced or buried, and bits on drill rigs would be estimated for depth • Many mining operations now utilize RTK GPS which significantly improves accuracy regarding depth of drilling as well as direction of tunneling

40. Utilities
• GPS can also be utilized in the utilities industry • Up-to-date maps of utilities are essential for utility companies – Maps allow companies to plan, build, and maintain their assets. • GPS can be used to gather precise location information about various lines, as well as any additional attribute information • Most line mapping requires little to no ground marking

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Forestry
• Applications in the forestry industry include – fire prevention and control – harvesting operations – insect patterns – boundary determinations – aerial spraying
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43. Factors affecting accuracy
Number of visible satellites
Position dilution of precision
Satellite elevations
Multipath
Distance between space station and rover receivers