GPS

1
GPS GIS An Introduction
2
Where Will This Take Us?

• What is GPS? What is GIS?
• How do GPS and GIS work?
• How will they help us?

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Find This!
3
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

4
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 receivers position

5
Major GPS Components
6
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

7
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 satellites clock

8
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

9
Error in Satellite Signals
DOP Dilution of Precision (This means that the
signal degrades)
10
Error in Satellite Signals
DOP projection for 23 January 2009 (Our data
collection day)
11
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

12
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

13
GIS Raster Data Model
ROWS
Grid Cell
COLUMNS
14
GIS Raster Data Model (cont)
House
Road
Archaeological Site
15
GIS Raster Data Model (cont)
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GIS Raster Data Model (cont)
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17
GIS Vector Data Model
House
Road
Archaeological Site
18
GIS Vector Data Model (cont)
House
Road
Archaeological Site
19
GIS Models - Combined

• Well use a combination of raster imagery and
  vector layer files to build our geo-database
• Lets see a real-world application