Geoapplications development

http://rgeo.wikience.org

Higher School of Economics, Moscow, www.cs.hse.ru

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

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).

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

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.

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.

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.

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

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

GPS satellite visibility 10

Minimum number of GPS satellites visible over 1 day, January 1, 2010

http://blogs.agi.com/navigationAccuracy/?p=315

GPS satellite visibility 11

Number of visible satellites

https://upload.wikimedia.org/wikipedia/commons/9/9c/ConstellationGPS.gif

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.

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.

GPS positioning in 2D: (lat, lon)

14

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).

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

GPS drawbacks: errors 17

http://www.iranmap.com/wordpress/wp-content/uploads/2010/04/gps-errors.jpg

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

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

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?

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”

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

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

WiFi calibration 24

Databases store fingerprinting data

However, they degrade over time

https://en.wikipedia.org/wiki/Wi-Fi_positioning_system

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

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

Readings 27

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Practical task 28

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