gps project training
DESCRIPTION
Training program for Geographic Positioning systemTRANSCRIPT
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Global Positioning SystemGlobal Positioning System
Geographic Information Systems Dep’tDavao Light and Power Company
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GPS History• US military began studies for improved
navigation system in mid-1960’s for: Cruise missiles Ballistic submarines Other strategic weapons purposes • Consolidated efforts were made in 1974 by
forming NAVSTAR GPS Joint Program OfficeFirst GPS satellite was launched in 1978Complete network of satellites in 1994
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NAVSTAR GPS
NA NAVIGATIONVS SYSTEMT TIMINGA AndR RANGING
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GPS Services
Standard Positioning Services (SPS)
- Unrestricted access provided to everyone
- Specified in Federal Radio Navigation Plan
- Accuracy – 100 meters 2D RMS. Further degradation in case of national emergency.
Precise Positioning Services (PPS)
- Restricted access, controlled by US Dep’t of Defense (DOD)
- Requires cryptographic equipment
- Accuracy – 16 meters 2D RMS
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GPS APPLICATIONS
• Navigation• Surveying• Mapping• Research• Plate Tectonic
• GIS• Construction• Tracking System• Geodetic Control• & Etc.
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GPS SEGMENTS
• SPACE SEGMENT
CONTROL SEGMENT
USER SEGMENT
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SPACE SEGMENT
• 24 Satellites• 6 Orbital Planes• 55o - 60o Inclination• 20,200 km Above Earth• 4-12 Visible Satellites• 12 hrs – Orbit• Max.5hrs Above
Horizon
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CONTROL SEGMENT
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USER SEGMENT
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How does GPS work?
GPS derivesposition relative tosatellite as“reference points,”
using trilateration.Not by triangulation.
The GPS unit on theground figures out itsdistance to each of severalsatellites
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Determining Positions
• GPS uses the principle of ranging (Distance from the satellite to the user) to determine positions.
• You need to know the range to at least 3 satellite signals in order to locate your position (X,Y of the Lat-Long) coordinates
• The fourth satellite signal will give you the 3rd dimension (the height or elevation) and the time dissemination
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Determining Positions
• To determine the distance to the satellite, you need to know how long a message takes you from the satellite.
• Distance = rate x time• The rate will be the speed of light (186,000 mi/sec
or 300,000 km/sec)• Time is the propagation time from the satellite to
the GPS receiver• Time is calculated using a clever technique of code
matching which compares signals from the satellite and GPS receiver
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Determining PositionsThe Sphere Concept
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ACCURACYThree Methods of Positioning Observation
Autonomous < 100 meters (SA on) < 12 meters (SA off)Differential 2 to 5 meters Submeter DecimeterPhase Differential Centimeter
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GPS Accuracy Issues
GPS position accuracy depends upon a number of issues:
Available Satellite GeometryAtmospheric Errors
Receiver ErrorsMulti-path Errors
Selective Availability
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Satellite GeometryPDOP (Positional Dilution of Precision)
The more separated thesatellites are – the
better the geometry, and the better the position solution
PDOP = Low
The closer the satellites are in the space, the worse the geometry, and the poorer the solution
PDOP = High
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GPS Receiver Categories
• Navigational Units- Mostly handheld units- Non-downloadable and non-DGPS- 5 to 10 meter level accuracy
• Mapping Grade- Handheld and pole mounted units- Downloadable and DGPS capable- Submeter to Decimeter accuracy
• Survey Grade- Usually mounted in tripod or pole- Downloadable and DGPS / RTK capable- Centimeter accuracy
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Navigational and Mapping Grade
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Survey Grade A New Era of Surveying
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THANK YOU!!!THANK YOU!!!