Semantic Trajectories in MobilityDB

MobilityDB is an open source software program that adds support for temporal and spatio-temporal objects to the PostgreSQL database and its spatial extension PostGIS.

This repository contains the code and the documentation for demonstrating semantic trajectories in MobilityDB using an hypothetical touristic dataset in Paris and a real-world pollution dataset in Delhi, India.

Installing MobilityDB

You must first install the MobilityDB extension in your system. We refer to the MobilityDB documentation for doing this. Please notice that the current release 1.3 of MobilityDB does not include the temporal JSON data type and thus it is necessary to build MobilityDB from the sources of the master branch. This can be done by first cloning the repository as show next.

git clone https://github.com/MobilityDB/MobilityDB

and then building the repository. Installing MobilityDB from the precompiled packages, for example using sudo apt install in Linux, does not work with this repository.

Input Data

The directory data contains the input files for the hypothetical touristic dataset in Paris. Loading this dataset can be done as follows.

Storing the Paris input data in PostgreSQL can be done as follows.

~/src/MobilityDB-Semantic$ createdb paris
~/src/MobilityDB-Semantic$ psql paris
psql (18.3)
Type "help" for help.

paris=# CREATE EXTENSION MobilityDB CASCADE;
NOTICE:  installing required extension "postgis"
CREATE EXTENSION
paris=# \i paris_tours.sql
psql:paris_tours.sql:3: NOTICE:  table "poi" does not exist, skipping
DROP TABLE
CREATE TABLE
INSERT 0 12
psql:paris_tours.sql:38: NOTICE:  table "tour" does not exist, skipping
DROP TABLE
CREATE TABLE
INSERT 0 39
psql:paris_tours.sql:93: NOTICE:  view "tourpoi" does not exist, skipping
DROP VIEW
CREATE VIEW
psql:paris_tours.sql:103: NOTICE:  table "temptour" does not exist, skipping
DROP TABLE
CREATE TABLE
INSERT 0 10

The data/ directory also expects the data from two-month pollution data in Delhi corresponding to the months of November and December, 2020 as well as the districts of New Delhi. The pollution data can be obtained from this link. Alternatively, you can find the data files in the following ZIP file. The contents of this ZIP file should be extracted into the data/ directory.

In order to get the districts of New Delhi we need to download OSM data from New Delhi obtained from the this link The file national_capital_territory_of_delhi.pbf must be located in the data/ directory.

We load the OSM data into PostgreSQL as follows.

osm2pgsql -U <user> -W -H localhost -P 5432 -d <database> --create --slim -G --hstore data/national_capital_territory_of_delhi.pbf

Then, we can execute the script that load the Delhi input data into PostgreSQL as follows.

~/src/MobilityDB-Semantic$ createdb delhi
~/src/MobilityDB-Semantic$ psql delhi
psql (18.3)
Type "help" for help.

delhi=# CREATE EXTENSION MobilityDB CASCADE;
NOTICE:  installing required extension "postgis"
CREATE EXTENSION
delhi=# CREATE EXTENSION hstore;
CREATE EXTENSION
delhi=# \timing
Timing is on.
delhi=# \i delhi_load.sql
DROP FUNCTION
Time: 13.130 ms
CREATE FUNCTION
Time: 6.883 ms
delhi=# select delhi_load();
NOTICE:  extension "mobilitydb" already exists, skipping
NOTICE:  extension "hstore" already exists, skipping
NOTICE:  Creating the table DelhiInput
NOTICE:  Inserting 2020-11-01_all.csv
[...]
NOTICE:  Inserting 2020-12-31_all.csv
NOTICE:  Creating tables WeatherInput and WeatherHourly
NOTICE:  Creating the table TripPoints
NOTICE:  Creating the table Trips
NOTICE:  Creating the table Grid
NOTICE:  Creating the table TripCells
NOTICE:  Creating the table TripTiles
NOTICE:  Creating the table Districts
NOTICE:  Creating tables PointDistricts and PointDistrictSeq
NOTICE:  Creating tables TripDistricts and TripDistrictsSeq
 delhi_load
------------

(1 row)

Time: 1441282.565 ms (24:01.283)
delhi=#

Queries

The queries can be found in the following files

• delhi_grid.sql: Queries for the trips segmented by the grid, both for the discrete and the continuous approaches
• delhi_districts.sql: Queries for the trips segmented by the districts, both for the discrete and the continuous approaches
• delhi_points_trips.sql: Queries for the complete trajectories, both for the discrete and the continuous approaches

License

The documentation of this evaluation is licensed under a Creative Commons Attribution-Share Alike 3.0 License