Difference between revisions of "Main Page/Stuff/Where y'at?"
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### Dangers | ### Dangers | ||
# Knowing location of one place implies knowing distances '''between''' places | # Knowing location of one place implies knowing distances '''between''' places | ||
− | ## How are distances measured? | + | ## How are long distances measured? |
# Ancient wonders were measured simply: distance and direction (measuring tapes, protractors, compasses) | # Ancient wonders were measured simply: distance and direction (measuring tapes, protractors, compasses) | ||
## Great Wall | ## Great Wall | ||
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=="Modern" location measurements== | =="Modern" location measurements== | ||
− | # WW2: Radio at the forefront of | + | # WW2: Radio & related technologies at the forefront of electronics |
## RADAR for detecting objects (friendly and enemy vehicles) | ## RADAR for detecting objects (friendly and enemy vehicles) | ||
## Development in to ground-based LORAN system | ## Development in to ground-based LORAN system | ||
Line 49: | Line 49: | ||
==Parts of the system== | ==Parts of the system== | ||
# Space segment | # Space segment | ||
− | #: 32 satellites in 6 orbital planes | + | #: 32 satellites in 6 orbital planes, started in early 1970s, fully functional in 1995 |
# Control segment: US DOD at AF bases | # Control segment: US DOD at AF bases | ||
# User segment: GPS units (base stations, cars, cell phones) | # User segment: GPS units (base stations, cars, cell phones) | ||
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## personnel, facilities, and equipment management | ## personnel, facilities, and equipment management | ||
# Civilian applications | # Civilian applications | ||
− | ## Transportation | + | ## Transportation (location and timing) |
## Safety (personal, e-911, etc.) | ## Safety (personal, e-911, etc.) | ||
## Find your friends | ## Find your friends | ||
+ | # Science | ||
+ | ## Mapping | ||
+ | ## precision timing | ||
+ | ## Continental drift, mountain building | ||
==Future of GPS== | ==Future of GPS== | ||
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# more advanced satellites, more advanced receivers | # more advanced satellites, more advanced receivers | ||
# additional locational technologies to augment GPS (WiFi, phone cells) | # additional locational technologies to augment GPS (WiFi, phone cells) | ||
+ | # Other systems (Russia, European Space Agency, China, India) | ||
# Privacy issues | # Privacy issues | ||
Latest revision as of 23:52, 29 September 2008
Contents
Where y'at? An introduction to Global Positioning Systems (GPS)
- Where y'at?
- New Orleans response
- Who knows their address?
- Who knows how to get home?
- Who knows the latitude and longitude of their home to 3 decimal places of precision?
Introduction to measurement of location
- Question has plagued humanity for ages
- Location of home
- Location of resources
- Water
- Food
- Dangers
- Knowing location of one place implies knowing distances between places
- How are long distances measured?
- Ancient wonders were measured simply: distance and direction (measuring tapes, protractors, compasses)
- Great Wall
- Pyramids
- Topographic survey of India, US, etc.
- Measurement methods did not change until the electronic age
"Modern" location measurements
- WW2: Radio & related technologies at the forefront of electronics
- RADAR for detecting objects (friendly and enemy vehicles)
- Development in to ground-based LORAN system
- More about LORAN technology later: basics are the same as GPS
- Cold war
- Missile launching, silo-to-silo
- knowledge of ground resources possible (high-altitude spy photo, satellite images)
- Most efficient killing machine: nuclear submarine
- Problem: how to surface quickly, get location, fire missile, and dive
- Solution: GPS, an extension of previously developed technologies
How does it work?
- d = r * t
- speed of light =~ 300,000,000 m/s
- satellite signals include satellite ID number and time of origin of signal
- demonstration
- one transit time = 1 distance = surface of a sphere, etc.
- simultaneous solution of 4 xyz equations
- demonstration (string)
- Precision timing: 1/1000 s error => 300,000 m error
- Receivers can keep good time over short intervals
- Receivers add or subtract very small amounts of time until a very precise estimate of location is made, time is fixed.
Parts of the system
- Space segment
- 32 satellites in 6 orbital planes, started in early 1970s, fully functional in 1995
- Control segment: US DOD at AF bases
- User segment: GPS units (base stations, cars, cell phones)
Sources of error
- low quality receivers
- insensitive electronics, errors in processing software & hardware
- cheap clocks
- multipathing (signals bouncing off buildings, etc.)
- atmospheric effects
- blunders (user error)
- selective availability (removed May 1, 2000)
- Added up to 100 m horizontal error by introducing clock errors
- Correcting errors
- more sensitive equipment
- more advanced on-board software (filtering multipath errors, e.g.)
- differential correction
- real-time differential correction
- Accuracy of typical handheld systems: 15 m at the worst, 1-5 m at best, varying under different conditions
Uses
- Military applications
- smart bombs
- personnel, facilities, and equipment management
- Civilian applications
- Transportation (location and timing)
- Safety (personal, e-911, etc.)
- Find your friends
- Science
- Mapping
- precision timing
- Continental drift, mountain building
Future of GPS
- Already in many new cars
- Telephones
- wrist watch size
- more advanced satellites, more advanced receivers
- additional locational technologies to augment GPS (WiFi, phone cells)
- Other systems (Russia, European Space Agency, China, India)
- Privacy issues
Where y'at?
- Third Place Books
- 122°18'22.785"W
- 47°40'33.193"N