GPS and GIS

1. GPS and GIS Bob E. Hall Center for Earth and Environmental Science Indiana University ~ Purdue University, Indianapolis

2. Location • Where am I? • Mapping • Where is It?(How do I get there?) • Navigation

3. Navigation Systems • Landmarks:Only work in local area. Subject to movement or destruction by environmental factors. • Dead Reckoning:Very complicated. Accuracy depends on measurement tools which are usually relatively crude. Errors accumulate quickly. • Celestial:Complicated. Only works at night in good weather. Limited precision. • OMEGA:Based on relatively few radio direction beacons. Accuracy limited and subject to radio interference. • LORAN:Limited coverage (mostly coastal). Accuracy variable, affected by geographic situation. Easy to jam or disturb. • SatNav:Based on low-frequency doppler measurements so it's sensitive to small movements at receiver. Few satellites so updates are infrequent.

7. Selective Availability

9. How GPS Works… • Triangulation

11. Pseudo-Random Code Comparing pseudo random codes that have a cycle width of almost a microsecond. At the speed of light a microsecond is almost 300 meters of error!

12. Almanac File – Perfect World Error from Earth-Moon-Sun Gravity and Solar Wind

13. Other Errors: Multipath Errors Geometric Dilution of Precision(GDOP)

14. How GPS Works… • Time Error Estimated Correction

24. Types of GPS Equipment • Trimble Total Station ($40k) • Trimble ProXRS with Data Logger ($11k) • Trimble Pocket GPS with PDA ($500) • Generic Handheld Unit ($200)