GPS & GIS – An Introduction

? Where Will This Take Us? Find This! 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 Vector 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 ROWS Grid Cell COLUMNS

GIS – Raster Data Model (cont) House Road Archaeological Site

GIS – Raster Data Model (cont)

GIS – Raster Data Model (cont) R H R R R S S S R S S S S R S S S R S S

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