science

SensorThings API

SensorThings API is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SensorThings API rather than just read about it. In short: SensorThings API is an Open Geospatial Consortium (OGC) standard providing an open and unified framework to interconnect IoT sensing devices, data, and applications over the Web. It is an open standard addressing the syntactic interoperability and semantic interoperability of the Internet of Things.

Key takeaways

SensorThings API belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SensorThings API to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SensorThings API from memory before moving on to harder problems.

Reference excerpt

SensorThings API is an Open Geospatial Consortium (OGC) standard providing an open and unified framework to interconnect IoT sensing devices, data, and applications over the Web. It is an open standard addressing the syntactic interoperability and semantic interoperability of the Internet of Things. It complements the existing IoT networking protocols such CoAP, MQTT, HTTP, 6LowPAN. While the above-mentioned IoT networking protocols are addressing the ability for different IoT systems to exchange information, OGC SensorThings API is addressing the ability for different IoT systems to use and understand the exchanged information. As an OGC standard, SensorThings API also allows easy integration into existing Spatial Data Infrastructures or Geographic Information Systems. OGC SensorThings API has two parts: (1) Part I - Sensing and (2) Part II - Tasking. OGC SensorThings API Part I - Sensing was released for public comment on June 18, 2015. The OGC Technical Committee (TC) approves start of electronic vote on December 3, 2015, and the SensorThings API Part I - Sensing passed the TC vote on February 1, 2016. The official OGC standard specification was published online on July 26, 2016. In 2019 the SensorThings API was also published as a United Nation's ITU-T Technical Specification. OGC SensorThings API Part II - Tasking Core was released for public comment on February 20, 2018, and it passed the TC vote on June 1, 2018. The official OGC standard specification for the SensorThings API Part II - Tasking Core was published online on January 8, 2019. In order to offer a better developer experience, the SensorThings API Part II - Tasking Core Discussion Paper was published online on December 18, 2018. The Tasking Core Discussion paper provides 15 JSON examples showing how SensorThings API Part II - Tasking Core can be used.

Design SensorThings API is designed specifically for resource-constrained IoT devices and the Web developer community. It follows REST principles, the JSON encoding, and the OASIS OData protocol and URL conventions. Also, it has an MQTT extension allowing users/devices to publish and subscribe updates from devices, and can use CoAP in addition to HTTP.

The foundation of the SensorThings API is its data model that is based on the ISO 19156 (ISO/OGC Observations and Measurements), that defines a conceptual model for observations, and for features involved in sampling when making observations. In the context of the SensorThings, the features are modelled as Things, Sensors (i.e., Procedures in O&M), and Feature of Interests. As a result, the SensorThings API provides an interoperable Observation-focus view, that is particularly useful to reconcile the differences between heterogeneous sensing systems (e.g., in-situ sensors and remote sensors). An IoT device or system is modelled as a Thing. A Thing has an arbitrary number of Locations (including 0 Locations) and an arbitrary number of Datastreams (including 0 Datastreams). Each Datastream observes one ObservedProperty with one Sensor and has many Observations collected by the Sensor. Each Observation observes one particular FeatureOfInterest. The O&M based model allows SensorThings to accommodate heterogeneous IoT devices and the data collected by the devices. SensorThings API provides two main functionalities, each handled by a part. The two profiles are the Sensing part and the Tasking part. The Sensing part provides a standard way to manage and retrieve observations and metadata from heterogeneous IoT sensor systems, and the Sensing part functions are similar to the OGC Sensor Observation Service. The Tasking part provides a standard way for parameterizing - also called tasking - of task-able IoT devices, such as sensors or actuators. The Tasking part functions are similar to the OGC Sensor Planning Service. The Sensing part is designed based on the ISO/OGC Observations and Measurements (O&M) model, and allows IoT devices and applications to CREATE, READ, UPDATE, and DELETE (i.e., HTTP POST, GET, PATCH, and DELETE) IoT data and metadata in a SensorThings service.

Entities (resources) SensorThings API Part I - Sensing defines the following resources. As SensorThings is a RESTful web service, each entity can be CREATE, READ, UPDATE, and DELETE with standard HTTP verbs (POST, GET, PATCH, and DELETE):

Thing: An object of the physical world (physical things) or the information world (virtual things) that is capable of being identified and integrated into communication networks. Locations: Locates the Thing or the Things it associated with. HistoricalLocations: Set provides the current (i.e., last known) and previous locations of the Thing with their time. Datastream: A collection of Observations and the Observations in a Datastream measure the same ObservedProperty and are produced by the same Sensor. ObservedProperty : Specifies the phenomenon of an Observation. Sensor : An instrument that observes a property or phenomenon with the goal of producing an estimate of the value of the property. Observation: Act of measuring or otherwise determining the value of a property. FeatureOfInterest: An Observation results in a value being assigned to a phenomenon.The phenomenon is a property of a feature, the latter being the FeatureOfInterest of the Observation. In addition to the above sensing resources, SensorThings API Part II - Tasking Core defines the following resources:

TaskingCapabilities: Specifies the task-able parameters of an actuator. Tasks: A collection of Tasks that has been created. Actuator : A type of transducer that converts a signal to some real-world action or phenomenon.

Example payload http://example.org/v1.0/Datastream(id)/Observations

Data array extensions In order to reduce the data size transmitted over the network, SensorThings API data array extension allows users to request for multiple Observation entities and format the entities in the dataArray format. When a SensorThings service returns a dataArray response, the service groups Observation entities by Datastream or MultiDatastream, which means the Observation entities that link to the same Datastream or the same MultiDatastream are aggregated in one dataArray.

Example request for data array http://example.org/v1.0/Observations?$resultFormat=dataArray

Example data array response

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with SensorThings API

Start with the simplest possible case. Write down what SensorThings API claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SensorThings API before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SensorThings API ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SensorThings API

In research: SensorThings API appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SensorThings API in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SensorThings API is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geographic information systems, Internet of things, Open Geospatial Consortium, so understanding it makes those chapters shorter.
In everyday life: Look for SensorThings API outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study SensorThings API in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SensorThings API means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SensorThings API out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SensorThings API in simple terms?

Why does SensorThings API matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SensorThings API?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SensorThings API.