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Introduction to GPS Global Positioning System

This introduction to GPS covers the basics of how GPS works, the types of GPS units available, and their functions such as track logging, storing waypoints, and navigating routes. Gain an understanding of GPS technology and learn how to choose and use a GPS unit effectively.

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Introduction to GPS Global Positioning System

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  1. Introduction to GPSGlobal Positioning System • Understanding GPS • Buying a GPS Unit • Using a GPS Unit Chad Sperry WIU GIS Center

  2. Understanding GPS What does GPS do? Answers the question -“Where am I?” How? – by computing a 3D coordinate

  3. Understanding GPS • Satellite Based Navigation • 24 Geosynchronous Satellites in Orbit • 20,200 kilometer altitude • 11 hours 58 minutes orbital period • 6 to 10 satellites always in view • Implemented by DoD • 24/7/365 • World-Wide Coverage • Operates Under “All” Weather Conditions • Prefers Line-of-Site • No Cost to End Users (FREE!!)

  4. Understanding GPS How is a GPS Signal Measured? Station A * If a train leaves Station A at 0600 and is traveling at 60 miles per hour. It arrives at Station B at 0900. How far did it travel? Station B Answer: Change in Time x Speed = Distance (0600-0900) x 60 = 180 miles

  5. Understanding GPS • Three Main Types of GPS • Consumer Grade • $100-$500 • Can record waypoints • Sufficient for many tasks • 10-20 foot accuracy • Mapping Grade • $3-$5k • Designed for data collection • Sub-Meter accuracy • Post-Processed • Survey Grade • $30-$50k • Centimeter level accuracy

  6. GPS Range Measurement Accuracy Error Source SPS PPS Selective Availability 0.0 0.0 Atmospheric Error Ionospheric 7.0 0.01 Tropospheric 0.7 0.7 Clock & Ephemeris Error 3.6 3.6 Receiver Noise 1.5 0.6 Multipath 1.2 1.8 Total User Equivalent Range Error, 1drms 8.1 4.1 Typical Horizontal DOP 2.0 2.0 Total Stand-Alone Horizontal 32.4 16.4Accuracy, 2 drms *Note: All Measurements in Meters Source: Charting the Future, NAPA/NRC, May, 1995.

  7. Understanding GPS • Consumer Grade Units • What do they do?

  8. Understanding GPS Track log Breadcrumb trail of where you’ve been Waypoints Allows a user to store a location and return at a future date – Prize Trees!! Routes Navigate between multiple waypoints

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