Location Based Service

User Location

• Cell Tower
• Wi-Fi
• GPS

Cell Tower

Wi-Fi

• The device determines the location of each access point by looking it up in a Wi-Fi location database.
• It then estimates its own location based on the found locations and their signal strength using trilateration.

GPS

• Why does GPS positioning require four satellites?

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Map Projections

Mercator

• Google Maps
• Bing Maps

Find POI Nearby

SQL Approach

• Select * from Places where Latitude between X-D and X+D and Longitude between Y-D and Y+D

What’s geohash

Construct a �geohash

• (37.77564, -122.41365) results in the binary sequence “0100110110010001111011110” and produces the geohash “9q8yy”.

Geohash Proximity Search

Geohash in Redis

• GEOADD
• GEODIST
• GEOHASH
• GEOPOS
• GEORADIUS
• GEORADIUSBYMEMBER
• GEOSEARCH
• GEOSEARCHSTORE

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Rideshare

Quadtree

Driver Location

• Quadtree partition
• Real-time location

Google S2

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Uber H3

• The H3 grid is constructed by laying out 122 base cells over the Earth, with ten cells per face. Some cells are contained by more than one face. Since it is not possible to tile the icosahedron with only hexagons, twelve pentagons are introduced, one at each of the icosahedron vertices. 

Thank you!