Difference between revisions of "Main Page/Stuff/Where y'at?"

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Line 23: Line 23:
 
#: Measurement methods did not change until the electronic age
 
#: Measurement methods did not change until the electronic age
  
−
=="Modern" location measurements
+
=="Modern" location measurements==
 
# WW2: Radio at the forefront of electronic technology
 
# WW2: Radio at the forefront of electronic technology
 
## RADAR for detecting objects (friendly and enemy vehicles)
 
## RADAR for detecting objects (friendly and enemy vehicles)
Line 33: Line 33:
 
## Most efficient killing machine: nuclear submarine
 
## Most efficient killing machine: nuclear submarine
 
#: Problem: how to surface quickly, get location, fire missile, and dive
 
#: Problem: how to surface quickly, get location, fire missile, and dive
−
#: Solution: GPS
+
#: 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
 +
# 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
 +
## Safety (personal, e-911, etc.)
 +
## Find your friends
 +
 +
==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)
 +
# Privacy issues
 +
 +
==Where y'at?==
 
* Third Place Books
 
* Third Place Books
 
*: 122°18'22.785"W   
 
*: 122°18'22.785"W   
 
*: 47°40'33.193"N
 
*: 47°40'33.193"N

Revision as of 23:38, 29 September 2008

Where y'at? An introduction to Global Positioning Systems (GPS)

  1. Where y'at?
    1. New Orleans response
  2. Who knows their address?
  3. Who knows how to get home?
  4. Who knows the latitude and longitude of their home to 3 decimal places of precision?

Introduction to measurement of location

  1. Question has plagued humanity for ages
    1. Location of home
    2. Location of resources
      1. Water
      2. Food
      3. Dangers
  2. Knowing location of one place implies knowing distances between places
    1. How are distances measured?
  3. Ancient wonders were measured simply: distance and direction (measuring tapes, protractors, compasses)
    1. Great Wall
    2. Pyramids
    3. Topographic survey of India, US, etc.
    Measurement methods did not change until the electronic age

"Modern" location measurements

  1. WW2: Radio at the forefront of electronic technology
    1. RADAR for detecting objects (friendly and enemy vehicles)
    2. Development in to ground-based LORAN system
      1. More about LORAN technology later: basics are the same as GPS
  2. Cold war
    1. Missile launching, silo-to-silo
    knowledge of ground resources possible (high-altitude spy photo, satellite images)
    1. 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?

  1. d = r * t
    1. speed of light =~ 300,000,000 m/s
    2. satellite signals include satellite ID number and time of origin of signal
  2. demonstration
    one transit time = 1 distance = surface of a sphere, etc.
    simultaneous solution of 4 xyz equations
    demonstration (string)
  3. 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

  1. Space segment
    32 satellites in 6 orbital planes
  2. Control segment: US DOD at AF bases
  3. User segment: GPS units (base stations, cars, cell phones)

Sources of error

  1. low quality receivers
  2. insensitive electronics, errors in processing software & hardware
  3. cheap clocks
  4. multipathing (signals bouncing off buildings, etc.)
  5. atmospheric effects
  6. blunders (user error)
  7. selective availability (removed May 1, 2000)
    Added up to 100 m horizontal error by introducing clock errors
  8. Correcting errors
    1. more sensitive equipment
    2. more advanced on-board software (filtering multipath errors, e.g.)
    3. differential correction
      1. real-time differential correction
  9. Accuracy of typical handheld systems: 15 m at the worst, 1-5 m at best, varying under different conditions

Uses

  1. Military applications
    1. smart bombs
    2. personnel, facilities, and equipment management
  2. Civilian applications
    1. Transportation
    2. Safety (personal, e-911, etc.)
    3. Find your friends

Future of GPS

  1. Already in many new cars
  2. Telephones
  3. wrist watch size
  4. more advanced satellites, more advanced receivers
  5. additional locational technologies to augment GPS (WiFi, phone cells)
  6. Privacy issues

Where y'at?

  • Third Place Books
    122°18'22.785"W
    47°40'33.193"N
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