gps & gis – an introduction. where will this take us? what is gps? what is gis? how do gps and...
TRANSCRIPT
GPS & GIS – An
Introduction
Where Will This Take Us?• What is GPS? What is GIS?• How do GPS and GIS work?• How will they help us?
? Find
This!
What is GPS?
• GPS stands for Global Positioning System
• GPS is a satellite navigation system designed to provide accurate position, velocity, and time information almost anywhere in the world
• the present system is known as NAVSTAR - NAVigation Satellite Timing And Ranging
• the GPS program operated and controlled by the US Department of Defense
How does GPS work?
• Each satellite broadcasts its orbital position as a modulated signal
• Receiver determines the difference between the time signal from the satellite and its own internal clock
• The distance from the satellite can be calculated using the speed of light (300,000 km/second)
• Position and distance from 3 or 4 satellites allows triangulation of receiver’s position
Major GPS Components
Space Segment
• A constellation of 24 orbiting satellites with 3-4 spares
• Orbit at a distance of 11,000 miles
• Each satellite contains several very precise atomic clocks
• orbit roughly every 12 hours, but they are not geosynchronous
Control Segment
• There are five Control Stations around the world• Stations monitor satellites as they pass
overhead by measuring the distance from the Control Station to the satellites
• Master Control Station determines satellite conditions (orbit, clock, health status) and calibrates the satellite’s clock
User Segment• Accuracy is dependent on the kind of receiver • Navigation (Recreation) grade – least
accurate• Mapping grade – accurate• Survey grade – most accurate• Costs range from $100 to $30,000
Error in Satellite Signals
DOP = Dilution of Precision (This means that the signal degrades)
Error in Satellite Signals
DOP projection for 23 January 2009 (Our data collection day)
Geographic Information Systems - GIS
• GIS is a spatial database with a strong visual display component
• GIS is not primarily a mapping program
• GIS was developed in the early 1980s, but its acceptance and development outside of the environmental sciences has been slow
GIS Data Models
• Raster Model– The first GIS model developed– Based on grids of cells that are assigned
values and grouped into layers
• Vector Model– Uses points, lines, and polygons define
data classes– Grouped into themes or layers
GIS – Raster Data Model
COLUMNS
GridCell
ROWS
GIS – Raster Data Model (cont)
House
Archaeological Site
Road
GIS – Raster Data Model (cont)
GIS – Raster Data Model (cont)
S S
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S S
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R
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H
0 0
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GIS – Vector Data Model
House
Road
Archaeological Site
GIS – Vector Data Model (cont)
House
Road
Archaeological Site
GIS Models - Combined
• We’ll use a combination of raster imagery and vector layer files to build our geo-database
• Let’s see a real-world application