Geofence Tracker

Problem

We consider the world is flat, and covered by a square grid.

A geofence is a geographic area where we want to track users. We consider circular geofences only.

A geofence hit is defined as when a user stays more than 10 minutes within a geofence. We consider we have a regular tracking of the position of our users.

We have a static list of geofences, for each one we have its center position (x, y), its radius and its name. Geofence: int x, int y, double radius, string name

Write a class that, having initially the list of geofences, receives a stream of users’ positions (string user_id, int x, int y, long timestamp) and produce geofence hits for these users.

Dataset example:

• With fences (x, y, radius, name).
  • 1, 1, 1.0, “fence 1”
  • 10, 10, 2.0, “fence 2”
• And stream (id, x, y, times in minutes):
  • “User1”, 0, 0, 0
  • “User2”, 0, 0, 0
  • “User1”, 1, 1, 1 // User 1 enters the fence 1
  • “User1”, 1, 1, 15 // User 1 have been in the fence 1 for > 10 min -> trigger
  • “User2”, 10, 11, 16 // User 2 enters the fence 2
  • “User2”, 10, 9, 25 // User 2 is still inside fence 2, but for 9 minutes.
  • “User2”, 1, 1, 30 // User 2 left fence 2 -> no trigger.
  • “User1”, 1, 1, 35 // User 1 is still in fence 1, but we already triggered.
• The output should therefore be:
  • User 1, fence 1, time 15.

Problem by Nicolas Defranoux @ Situ8ed SA

Solution

The solution is based on the Observer Design Pattern. Geofences are observers subscribed to user's positions stream.

cf : https://sourcemaking.com/design_patterns/observer

Geofences

10 Geofences are randomly generated in a 500x500 square World.

• The radius is between 50 and 100.
• Geofences are fully inside the world
  • Foreach Geofence(x,y,radius), x >= radius AND y>= radius AND (500-x) >= x AND 500-y >= y

Users

4 Users moves in the world with a random path (Gaussian distribution).

• A user starts at the (0,0) point and allways stay in the world.

DataVisualization

To run the DataViz run a HTTPServer inside the /dataviz folder python -m SimpleHTTPServer 8000 for example. Then go in a web browser to the http://localhost:8000/ address.

The com.roche.geofence.jsonlog package is used to log Geofences and Users position in JSON format used by D3.JS in the datavisualization.