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

G

lobal

P

ositioning

S

ystem •

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 -

NAV

igation

S

atellite

T

iming

A

nd

R

anging • 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 Grid Cell

COLUMNS

GIS – Raster Data Model (cont) House Archaeological Site

GIS – Raster Data Model (cont)

GIS – Raster Data Model (cont) 0 0 0 0 0 0 R 0 R 0 0 H 0 0 R 0 0 0 0 0 0 0 0 0 0 R R R 0 S S R 0 0 0 S S S S 0 0 0 0 0 0 S S S 0 0 0 0 S S S 0 0 0 0 0 0 0 0

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