11. Sensors

Originally the SE Platform was developed for a single sensor device (station), the Intemo Jose(ne). As time moved on additional sensor devices from various sensor projects were integrated, or are in progress. To allow for multiple sensor stations/devices, each with multiple internal sensors from multiple projects, internals for mainly the ETL processes (cron jobs) were generalized while still keeping the core principles of the overall architecture and multi-step ETL processing: raw data harvesting (pull), refinement (validation, calibration), service-publication.

Based on device/sensor-types different ETL algorithms need to be applied. For example, some devices already emit calibrated sensor-values (Luftdaten, Osiris), others require ANN calibration (Jose), others even per-sensor linear or polynominal equations, sometimes per-sensor (AirSensEUR AlphaSense).

The advantage of the current approach is that once measurements are ‘in’, they become automatically available through all external APIs without any additional action. Only on the ‘input’ (harvesting)-side and refinement ETL are specific formatting steps required.

11.1. Principles

To integrate a new sensor station type, two main items need to be resolved:

  • APIs from which sensor-data can be harvested (‘getting the raw or sometimes calibrated data in’)
  • amount/complexity of calibration and validation needed

In addition, a sensor station type is usually related to a Project. In an early stage every device was given a unique id, where the first 4 digits is the project id, followed by additional digits, denoting the station id within that project. Sometimes a mapping is required. The original station id is always kept in metadata columns.

11.1.1. APIs

Data from sensors is never sent directly to the SE platform. It is sent to what are called Data Collectors. These are usually not maintained by SE but by the specific projects like Smart City Living Lab, Luftdaten and/or companies like Intemo etc. The only requirement is that these Data Collectors provide APIs for pulling data into (Harvesting) the SE Platform.

Currently, harvesting from three Data Collector APIs has been realized:

  1. Raw Sensor (a.k.a. Whale) API from now mainly Intemo (Jose stations) servers
  2. InfluxDB Data Collector API, now mainly for AirSensEUR stations
  3. Luftdaten API, for Luftdaten.info kits

Ad 2) this InfluxDB API is maintained by the SE Project itself and may be used in later projects to publish (push) data from additional sensors.

11.1.2. Calibration

Currently, the following calibration algorithms are implemented:

  1. Jose stations: ANN Calibration
  2. AirSensEUR per-sensor linear or polynominal equations
  3. Luftdaten.info : no calibration required

These algorithms are reusable, mainly the parameters for each need to be set.

So how is this realized internally? Basic principles:

  • while harvesting as much metadata as possible is extracted or configured
  • the programming concept of an abstract Device and Device registry

Each station-type (Jose, ASE, Luftdaten) is mapped to a Device Type. From there, specific processing, configuration and algorithms are invoked. A special Device Type is the Vanilla Device. The Vanilla Device Type can be used when no specific calibration is required. This is the easiest way to attach stations and was introduced when attaching kits from the Luftdaten Project .

Each Device has one to three additional items/files:

  • Device Definitions (“device devs”), these map component indicators like no2, temperature etc to their raw inputs and provides pointers to the functions that perform converting (e.g. via calibration) the raw inputs, plus min/max values for validation
  • Device Functions: functions that provide all conversions/calibrations
  • Device Params (AirSensEUR-AlphaSense sensors only): per-device calibration params

The Refiner mainly invokes these as abstract items without specific knowledge of the Device or sensor type.


  1. Jose Stations:
  1. AirSensEUR Stations:
  1. Luftdaten Kits (using Vanilla Device):

11.2. Additional Info

Some specifics per station type and projects.

11.2.1. Luftdaten Kits

With the introduction of the Vanilla Device only specific Harvesting classes needed to be developed:

  • Last Values harvesting - using the “last 5 minute values” API
  • General harvesting - using the “last hour average values” API

As to not strain the Luftdaten server intrastructure and to start lightly, only data in specified Bounding Boxes within the ETL Stetl config, is harvested. In first instance the area of Nijmegen, [51.7,5.6,51.9,6.0], but this can be extended later.

Only three classes are required integrating Luftdaten measurements, the first is a common base-class for all:

These classes mainly process incoming JSON-data to required database record formats for generic Stetl PostgresInsert output classes.

The Stetl configurations as run in the ETL cronjobs are:

Device id’s consist of a fixed project id, 4931 (German and Dutch country codes) followed by 4-5 digits Luftdaten Location id. Although each LTD sensor has its own unique id, the Location Id (and related lat/lon) binds multiple sensors together and can be considered as a “kit” or “station”.

No specific code is required for any of the other SE ETL processes, like Refiner and SOS and STA Publishers. For example all Luftdaten STA Things can be queried by the project id 4931: https://data.smartemission.nl/gost/v1.0/Things?$filter=properties/project_id%20eq%20%274931%27

11.2.2. AirSensEUR

To Be Supplied.

Project id is 1182.

Via STA: https://data.smartemission.nl/gost/v1.0/Things?$filter=properties/project_id%20eq%20%271182%27

11.2.3. Josene

To Be Supplied.

Several projects including Smart City Living Lab, Waalkade. The original Nijmegen SE project has project id ‘0000’, others usually start with ‘2’.