Geoapplications development · Geoapplications development Higher School of Economics, Moscow,
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Transcript of Geoapplications development · Geoapplications development Higher School of Economics, Moscow,
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Geoapplications development
http://rgeo.wikience.org
Higher School of Economics, Moscow, www.cs.hse.ru
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Signal-based positioning 2
Satellite-based,
e.g. GPS
Beacons https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSYYC7irjytoGY7XaURz3UeRCWkK_pcKVBCBhGKCCnZ64MG4CQo http://www.steelintheair.com/imgs/new-cell-tower-lease.jpg http://www.smbretail.com/wp-content/uploads/2015/12/tumblr_inline_ndeolbm5PR1rd9i5u.png
Cellular
WiFi
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GPS applications Tracking of birds and animals
http://dx.plos.org/10.1371/journal.pone.0039833;jsessi
Osprey (blue), Marsh Harrier (green), Egyptian Vulture (orange), Short-toed Eagle (red).
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GPS applications CYGNSS – Cyclone Global Navigation Satellite System Innovation: retrieve wind speed of tropical cyclones in presence of clouds + with high frequency To be launched in 2 days:
https://www.nasa.gov/cygnss
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GPS applications
Precision gunfire
http://www.nbcnews.com/technology/how-tomahawk-cruise-missiles-send-message-syria-8C11022222
The most advanced Tomahawks fly at 550 mph, have GPS, onboard digital maps, video cameras, two-way satellite links and a navigation system that allows them to loiter over an area and wait for their targets to pop up. That's in addition to the 1,000-pound bomb each Tomahawk typically carries.
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GPS applications
Precision agriculture
https://www.gps4us.com/news/post/Global-positioning-and-geographic-information-systems-help-create-an-environmentally-friendly-farm-20111228.aspx
The precision farming integrated solution includes suite of GPS and GIS enabled applications which together are being used for farm planning, field mapping, soil sampling, tractor guidance, crop scouting, variable rate applications, and yield mapping.
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GPS applications
Railway
http://www.gps.gov/applications/rail/
Positive Train Control (PTC) systems prevent collisions, derailments, work zone incursions, and passage through switches in the wrong position.
A PTC system can automatically vary train speeds, re-route traffic, and safely direct maintenance crews onto and off tracks. PTC increases track capacity by maintaining a constantly updated operating plan that optimizes rail use and flow.
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GPS – Global Positioning System 8
1. Orbital segment
2. Control segment
3. User segment
http://image.slidesharecdn.com/pgdgi03seminarnavdeepsingh-140113095137-phpapp02/95/global-positioning-system-7-638.jpg?cb=1389607822
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GPS – Orbital Segment 9
Orbital segment: 21 satellites + 3 backup are sufficient to provide global coverage. Currently 31 GPS satellites orbiting the Earth.
http://www8.garmin.com/graphics/24satellite.jpg
The image shows 4 planes * 6 satellites
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GPS satellite visibility 10
Minimum number of GPS satellites visible over 1 day, January 1, 2010
http://blogs.agi.com/navigationAccuracy/?p=315
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GPS satellite visibility 11
Number of visible satellites
https://upload.wikimedia.org/wikipedia/commons/9/9c/ConstellationGPS.gif
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GPS – Ground Segment 12
Also called control segment or ground stations:
1. a master control station (MCS)
2. an alternate master control station
3. four dedicated ground antennas
4. six dedicated monitor stations
Satellites carry precise atomic clocks with nanoseconds accuracy.
The responsibility of a control segment is to periodically send current precise time and location to each satellite.
Ephemeris – position of satellite at a given time.
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GPS – User Segment 13
Cheap and small receivers
http://www.ainonline.com/aviation-news/aviation-international-news/2012-05-02/gps-jamming-prompts-renewed-interest-system-backup
One of the key differences between receivers is accuracy. Advanced equipment and advanced receivers increase accuracy.
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GPS positioning in 2D: (lat, lon)
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GPS positioning – 4 satellites for 3D (lat, lon, z) 15
https://openclipart.org/image/2400px/svg_to_png/191659/GPS-3D-trilateration.png
This and previous illustrations are idealized (case of having exact distance between receiver and transmitter).
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GPS math 16
https://openclipart.org/image/2400px/svg_to_png/191659/GPS-3D-trilateration.png
Distance between satellite and receiver = wave speed * time
• wave speed = speed of light = 186K miles/sec
• time?
o Satellite generates pseudo-random sequence and transmits it to receiver
o Receiver generates the same sequence as well
o After the sequence has arrived, receiver aligns it with its own sequence and finds time shift
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GPS drawbacks: errors 17
http://www.iranmap.com/wordpress/wp-content/uploads/2010/04/gps-errors.jpg
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GPS drawbacks: satellite visibility 18
There are cases when less than 4 satellites may be visible at a time
One of the ways around: add more satellites
http://www.geo.upm.es/postgrado/CarlosLopez/materiales/cursos/www.ncgia.ucsb.edu/education/curricula/giscc/units/u017/figures/figure15.gif
Other drawbacks – indoor navigation impossible, canyon effects (this image), slow (in cold receiver state), high battery power consumption, low accuracy in some cases
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GLONASS 19
Development started in Soviet Union, 1976
Now 24
Now 29 satellites on orbit (not all are active – mainly due to backup purposes and maintenance)
http://www.navigadget.com/wp-content/postimages/2011/11/glonass-map.jpeg
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GPS & GLONASS & Co 20
Several constellations increase sat. visibility.
Global only are
GLONASS – Russian
GPS – US
To be completed:
Galileo – EU
COMPASS – Chinese
https://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/Comparison_satellite_navigation_orbits.svg/2000px-Comparison_satellite_navigation_orbits.svg.png
Now GPS receivers leverage satellite signals both from GPS and GLONASS
Q: why are orbits so high?
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WiFi positioning 21
Works for notebooks and other devices without GPS modules
Works for indoor navigation
Every network device is manufactured with a unique MAC
Recall ARP (Address Resolution Protocol)
On Windows type “ipconfig -all”
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WiFi positioning 22
Basic idea – create mapping MAC (lat, lon) for all MACs
Fingerprinting
1 Calibration (offline phase) – MAC, signal strengths, location
2 Positioning (online phase) – worse than GPS, better than cellular
Accuracy ~ tens of meters
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WiFi calibration 23
Fingerprinting
1 Calibration (offline phase) – MAC, signal strengths, location (lat, lon)
2 Positioning (online phase) – worse than GPS, better than cellular
• War driving collects fingerprints for all visible WiFi points
• Volunteers, e.g. iPhones send fingerprint data anonymously to Apple
Requires no password or other authentication information
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WiFi calibration 24
Databases store fingerprinting data
However, they degrade over time
https://en.wikipedia.org/wiki/Wi-Fi_positioning_system
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WiFi positioning 25
Fingerprinting
1 Calibration (offline phase) – MAC, signal strengths, location
2 Positioning (online phase) – worse than GPS, better than cellular
The idea is similar to GPS; many algorithms exist to improve both phases
http://www.mobizen.pe.kr/attach/1/cfile27.uf.146D33355047FEFD04B938.gif
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Cellular positioning 26
Less accurate, ~ hundreds of meters, order of magnitude higher than WiFi
Same principles as in WiFi positioning
http://www.swri.org/3pubs/ird2002/images/16-9222.jpg
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Readings 27
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Practical task 28
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