EXPLORA-LD

This is a Kafka Streams implementation of the EXPLORA framework, which exposes a Linked Data Fragments interface, based on the AirQualityExpressServer.

Features

• Continuous computation of data summaries, as new data becomes available in Obelisk (Stream processors consume sensor readings from a Kafka topic).

• Three geo-indexing methods: Geohash, Quad-tiles and Slippy tiles (default: quad-tiles).

• Configurable resolution of the spatial fragmentation scheme (default: 14). Multiple resolutions can be specified.

• Data summaries are computed on a custom set of air quality variables supported by Obelisk (default: airquality.no2::number,airquality.pm10::number)

• Configurable time-series fragment size (default: 1 hour)

Architecture

Requirements

• A Kafka topic where the sensor observations from Obelisk are being posted. To get data from Obelisk into a Kafka topic you could use cot-see-consumer, which is an implementation of a client of the Server-Sent Events endpoint from Obelisk.

Running the server

Use the comands below to run one instance of the server on localhost:7070

$ docker build explora-ld .

$ docker run --name explora \
	-e METRICS="airquality.no2::number,airquality.pm10::number" \
	-e READINGS_TOPIC="<topic_name>" \
	-e APP_NAME="explora-ingestion" \
	-e KBROKERS="<kafka_host>:<kafka_port>" \
	-e GEO_INDEX="quadtiling" \
	-e PRECISION='14' \
	-e LD_FRAGMENT_RES="hour" \
	-e REST_ENDPOINT_HOSTNAME="0.0.0.0" \
	-e REST_ENDPOINT_PORT="7070" \
	explora-ld

Usage

Once the server is running you can query the data using the following template:

http://localhost:7070/data/14/{x}/{y}{?page,aggrMethod,aggrPeriod}

Where x and y are the coordinates of a certain tile and page is an ISO date that determines the day the air quality measurements were taken. aggrMethod and aggrPeriod define the used aggregation method and time interval for the aggregation respectively. Types for aggrMethod currently are avg, sum, and count. Types for aggrPeriod are min, hour and day. If these two parameters are undefined, the raw data is queried. For example:

http://localhost:7070/data/14/8392/5467?page=2020-05-26T00:00:00.000Z&aggrMethod=avg&aggrPeriod=hour