Connected Systems

What is OGC API - Connected Systems?

OGC API - Connected Systems, also known as the Connected Systems API, is built upon standardized web formats such as GeoJSON as well as existing OGC information models such as:

SensorML
Observations and Measurements (O&M) (now called Observations, Measurements, and Samples)
SWE Common Data Model
Semantic Sensor Network Ontology (SOSA/SSN)

OpenSensorHub and Connected Systems

OpenSensorHub has the most supported implementation of OGC API - Connected Systems. The Connected Systems API is the primary means of communication from OpenSensorHub node to OpenSensorHub node, as well as between some client application and an OpenSensorHub node or various nodes.

OpenSensorHub nodes are prepackaged with a running implementation of the Connected Systems API, which exposes all sensing systems, actuators, features, etc. on the OpenSensorHub node.

Understanding Parts 1 and 2

Feature Resources

Part 1 of OGC API - Connected Systems conforms to OGC API - Features.

Resources in Part 1 of the API are used to describe sensing systems, geographic features, both deployments and methodologies of systems, and other domain features.

Part 1 Feature Resources

Resource Name	Description
Systems	Systems are used to expose meta data about sensors, actuators, samplers, processes, platforms, etc.
Subsystems	Subsystems can be used for complex, hierarchical descriptions of systems. These are Systems that are exposed through a sub-collection of a parent System.
Deployments	Deployments provide information about the deployment of one or more Systems for a specific purpose.
Subdeployments	Subdeployments can be used to describe complex, hierarchical descriptions of deployments. These are Deployments that are exposed through a sub-collection of a parent Deployment.
Procedures	Procedures provide specifications or methodology implemented by a System to accomplish its task(s).
Sampling Features	Sampling Features provide information about a sampling strategy used when observing a Feature of Interest. Sampling Features are also used to identify the part of a Feature of Interest that is affected by an actuator or process in response to a command.
Property Definitions	Properties specify observable properties, controllable properties, and system properties.

tip

The most commonly used Feature Resources you will find as part of an OpenSensorHub node are Systems, Subsystems, and Sampling Features.

Dynamic Data Resources

Part 2 of OGC API - Connected Systems defines resource types that allow the provision of dynamic data for hardware components and processes which includes data from sensors, platforms, robots, human observers, forecase models, computer simulations, etc.

The dynamic data resources primarily focus on Observations of DataStreams and Commands of ControlStreams.

Part 2 Dynamic Data

Resource Name	Description
DataStreams	A DataStream represents data produced by an observing System feature. DataStreams expose real-time and archived data.
Observations	Observations are strictly associated to DataStreams as a single instance of an observation recorded from an observing System, described by the Observation's DataStream.
ControlStreams	A ControlStream represents a control channel used to change the state of a Feature Resource, such as a System. ControlStreams represent real-time control channels, but also expose archived commands.
Command	Commands are strictly associated to ControlStreams, representing a command that has been sent to its ControlStream, to task the ControlStream's corresponding Feature Resource.
CommandStatus	CommandStatus represents a status report describing the status of a Command at any point in time. Synchronously executed Commands will report `COMPLETED`, `REJECTED`, or `FAILED`.
SystemEvents	SystemEvents are used to notify users of changes to one or more Systems

OSHConnect

Now that we have covered the basics of OGC API - Connected Systems, we can revisit the idea of OSHConnect.

Again, OSHConnect is a family of client libraries that provides support for interfacing with an OpenSensorHub instance or instances via the Connected Systems API. Therefore, OSHConnect provides client tools and helper methods to access Systems, DataStreams / Observations, ControlStreams / Commands, while giving you the flexibility to subscribe to real-time streams or retrieve archived data.

OSHConnect also provides helper methods to create Feature and Dynamic Data Resources that you can push to OpenSensorHub nodes via the Connected Systems RESTful interface.

Hands-on Guide and Examples

These examples will be using the GeoRobotix test node, which is an OpenSensorHub node used for testing and client examples.

The Connected Systems API for this test server is accessible at

https://api.georobotix.io/ogc/demo1/api

tip

OpenSensorHub offers an easily navigable web interface to explore the Connected Systems API. Try visiting the API in your browser!

When querying Feature Resources such as Systems or Sampling Features, we can ask for these resources in JSON, encoded with SensorML or GeoJSON.

Dynamic Data Resources are modeled with the SWE Common Data Model

Systems

Sending an HTTP GET request to the following endpoint will yield us a list of all systems exposed through the API.

https://api.georobotix.io/ogc/demo1/api/systems

The request will return the following:

SensorML JSON
GeoJSON

{
    "items": [
    {
        "type": "PhysicalSystem",
        "id": "ki7dgdg90mqt6",
        "uniqueId": "urn:osh:sensor:uas:predator001-RT",
        "definition": "http://www.w3.org/ns/ssn/System",
        "label": "Predator UAV (MISB simulated RT)",
        "validTime": [
        "2023-05-14T15:22:00Z",
        "now"
        ]
    }, 
    ...
    ]
}

{
    "items": [
    {
        "type": "Feature",
        "id": "ki7dgdg90mqt6",
        "geometry": null,
        "properties": {
            "uid": "urn:osh:sensor:uas:predator001-RT",
            "featureType": "http://www.w3.org/ns/ssn/System",
            "name": "Predator UAV (MISB simulated RT)",
            "validTime": [
            "2023-05-14T15:22:00Z",
            "now"
            ]
        }
    },
    ...
    ]
}

As you can see, each system has an id property. This identifier is used to access System descriptions, along with associated DataStreams and ControlStreams.

Request	Description
`/api/systems/{systemId}`	System Description
`/api/systems/{systemId}/subsystems`	System's Subsystems
`/api/systems/{systemId}/datastreams`	System's associated DataStreams
`/api/systems/{systemId}/controlstreams`	System's associated ControlStreams
`/api/systems/{systemId}/samplingFeatures`	System's associated SamplingFeatures

Using the first System as an example, we'll retrieve the System description.

https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6

Response:

SensorML JSON
GeoJSON

{
    "type": "PhysicalSystem",
    "id": "ki7dgdg90mqt6",
    "uniqueId": "urn:osh:sensor:uas:predator001-RT",
    "definition": "http://www.w3.org/ns/ssn/System",
    "label": "Predator UAV (MISB simulated RT)",
    "validTime": [
        "2023-05-14T15:22:00Z",
        "now"
    ]
}

{
    "type": "Feature",
    "id": "ki7dgdg90mqt6",
    "geometry": null,
    "properties": {
        "uid": "urn:osh:sensor:uas:predator001-RT",
        "featureType": "http://www.w3.org/ns/ssn/System",
        "name": "Predator UAV (MISB simulated RT)",
        "validTime": [
        "2023-05-14T15:22:00Z",
        "now"
        ]
    },
    "links": [
        {
        "rel": "canonical",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6",
        "type": "application/json"
        },
        {
        "rel": "alternate",
        "title": "Detailed description of system in SensorML format",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6?f=sml",
        "type": "application/sml+json"
        },
        {
        "rel": "alternate",
        "title": "Detailed description of system in HTML format",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6?f=html",
        "type": "text/html"
        },
        {
        "rel": "subsystems",
        "title": "List of subsystems",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6/subsystems?f=json",
        "type": "application/json"
        },
        {
        "rel": "datastreams",
        "title": "List of system datastreams",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6/datastreams?f=json",
        "type": "application/json"
        },
        {
        "rel": "controlstreams",
        "title": "List of system controlstreams",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6/controls?f=json",
        "type": "application/json"
        },
        {
        "rel": "samplingFeatures",
        "title": "List of system sampling features",
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6/samplingFeatures?f=json",
        "type": "application/json"
        }
    ]
}

tip

The response in GeoJSON also yields us links to other related System resources such as Subsystems, DataStreams, ControlStreams, and SamplingFeatures.

DataStreams

DataStream resources can be queried at the collection endpoint for DataStreams, or through referencing a particular System's DataStreams.

/api/datastreams

and

/api/systems/{systemId}/datastreams

We can use our previous System as an example of how to query and select a particular DataStream.

https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6/datastreams

Response (all DataStreams of our System):

{
  "items": [
    {
      "id": "15po2igbfnjjk",
      "name": "Predator UAV (MISB simulated RT) - GeoReferenced Image Frame",
      "system@id": "ki7dgdg90mqt6",
      "system@link": {
        "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6?f=json",
        "uid": "urn:osh:sensor:uas:predator001-RT",
        "type": "application/geo+json"
      },
      "outputName": "geoRefImageFrame",
      "validTime": [
        "2023-05-14T15:22:00Z",
        "now"
      ],
      "phenomenonTime": [
        "2025-06-06T20:29:05.117Z",
        "2025-06-06T20:39:05.252000244Z"
      ],
      "resultTime": [
        "2025-06-06T20:29:05.117Z",
        "2025-06-06T20:39:05.252000244Z"
      ],
      "observedProperties": [
        {
          "definition": "http://sensorml.com/ont/misb0601/property/FrameCenterLocation"
        },
        {
          "definition": "http://sensorml.com/ont/misb0601/property/FrameUpperRightCornerLocation"
        },
        {
          "definition": "http://sensorml.com/ont/misb0601/property/FrameLowerRightCornerLocation"
        },
        {
          "definition": "http://sensorml.com/ont/misb0601/property/FrameLowerLeftCornerLocation"
        },
        {
          "definition": "http://sensorml.com/ont/misb0601/property/FrameUpperLeftCornerLocation"
        }
      ],
      "resultType": "record",
      "formats": [
        "application/om+json",
        "application/swe+json",
        "application/swe+csv",
        "application/swe+xml",
        "application/swe+binary"
      ]
    },
    {
      "id": "98nto59268lok",
      "name": "Predator UAV (MISB simulated RT) - Platform Attitude",
      "system@id": "ki7dgdg90mqt6",
      ...
    },
    {
      "id": "6ft4mrvfugkr2",
      "name": "Predator UAV (MISB simulated RT) - Sensor Location",
      ...
    },
    {
      "id": "5lkdq857dt2l6",
      "name": "Predator UAV (MISB simulated RT) - UAS Video",
      ...
    }
  ]
}

For the sake of simplicity, we'll select the "Sensor Location" DataStream, by using its id (6ft4mrvfugkr2).

We can retrieve this DataStream through the collection endpoint for DataStreams, or through our System's DataStream collection.

/api/datastreams/{id}

/api/systems/{systemId}/datastreams/{datastreamId}

Retrieving our DataStream from /api/datastreams:

https://api.georobotix.io/ogc/demo1/api/datastreams/6ft4mrvfugkr2

{
  "id": "6ft4mrvfugkr2",
  "name": "Predator UAV (MISB simulated RT) - Sensor Location",
  "system@id": "ki7dgdg90mqt6",
  "system@link": {
    "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6?f=json",
    "uid": "urn:osh:sensor:uas:predator001-RT",
    "type": "application/geo+json"
  },
  "outputName": "sensorLocation",
  "validTime": [
    "2023-05-14T15:22:00Z",
    "now"
  ],
  "phenomenonTime": [
    "2025-06-06T20:36:05.118Z",
    "2025-06-06T20:46:48.12Z"
  ],
  "resultTime": [
    "2025-06-06T20:36:05.118Z",
    "2025-06-06T20:46:48.12Z"
  ],
  "observedProperties": [
    {
      "definition": "http://www.opengis.net/def/property/OGC/0/SensorLocation"
    }
  ],
  "resultType": "vector",
  "formats": [
    "application/om+json",
    "application/swe+json",
    "application/swe+csv",
    "application/swe+xml",
    "application/swe+binary"
  ],
  "links": [
    {
      "rel": "canonical",
      "href": "https://api.georobotix.io/ogc/demo1/api/datastreams/6ft4mrvfugkr2",
      "type": "application/json"
    },
    {
      "rel": "system",
      "title": "Parent system as GeoJSON",
      "href": "https://api.georobotix.io/ogc/demo1/api/systems/ki7dgdg90mqt6?f=application/geo+json",
      "type": "application/geo+json"
    },
    {
      "rel": "observations",
      "title": "Collection of observations",
      "href": "https://api.georobotix.io/ogc/demo1/api/datastreams/6ft4mrvfugkr2/observations"
    }
  ]
}

We can see that this DataStream object gives us the output name, observed properties, data type, and other useful information.

Observations

If we want to retrieve observations from this DataStream, we can simply go to the Observations collection on this DataStream.

/api/datastreams/{datastreamId}/observations

Retrieving the DataStream's Observations:

https://api.georobotix.io/ogc/demo1/api/datastreams/6ft4mrvfugkr2/observations

{
  "items": [
    {
      "id": "ogc00th28ee5tj52lj8rjmkang",
      "datastream@id": "6ft4mrvfugkr2",
      "foi@id": "lsp05mnn1dfn2",
      "phenomenonTime": "2025-06-06T20:40:05.118Z",
      "resultTime": "2025-06-06T20:40:05.118Z",
      "result": {
        "location": {
          "lat": 34.69819220933048,
          "lon": -86.66536597845395,
          "alt": 3047.812619211108
        }
      }
    },
    {
      "id": "8trbhispt33eu31ems7fp27j5c",
      "datastream@id": "6ft4mrvfugkr2",
      "foi@id": "lsp05mnn1dfn2",
      "phenomenonTime": "2025-06-06T20:40:05.152Z",
      "resultTime": "2025-06-06T20:40:05.152Z",
      "result": {
        "location": {
          "lat": 34.69819950158624,
          "lon": -86.66533982691604,
          "alt": 3047.812619211108
        }
      }
    },
    {
      "id": "4a5vdif0vau8hgbeg82lstohus",
      "datastream@id": "6ft4mrvfugkr2",
      ...
  ],
  "links": [
    {
      "rel": "next",
      "href": "https://api.georobotix.io/ogc/demo1/api/datastreams/6ft4mrvfugkr2/observations?offset=100",
      "type": "application/om+json"
    }
  ]
}

The response yields us a paginated list of this DataStream's Observations, which includes timestamps and the result data block.

What is OGC API - Connected Systems?​

OpenSensorHub and Connected Systems​

Understanding Parts 1 and 2​

Feature Resources​

Dynamic Data Resources​

OSHConnect​

Hands-on Guide and Examples​

Systems​

DataStreams​

Observations​