14. STA Example Requests

Workflow Overview

This section explains by an example how to create and read data in the Sensor Things API (STA). The example is a weather station at the 52°North GmbH office building which measures the air temperature and the air pressure. The STA data model groupes the data in the following classes which are called entities:

Thing, a Thing is an object of the physical world or the information world that is capable of being identified and integrated into communication networks (here: weather station)
Location, the Location entity locates the Thing or the Things it associated with (here: 52°North GmbH office building)
HistoricalLocation, a Thing's HistoricalLocation entity set provides the times of the current and previous location of the Thing
Datastream, a Datastream groups a collection of Observations meauring the same Observedproperty and produced by the same Sensor (here: collection of thermometer observation or barometer observations)
Sensor, a Sensor is an instrument that observes a property or phenomenon with the goal of producing an estimate of the value of the property (here: thermometer and barometer)
ObservedProperty, an ObservedProperty specifies the phenomenenon of an Observation (here: air temperature and air pressure)
Observation, an Observation is the act of measuring or otherwise determining the value of a property (here: observations by the thermometer and barometer)
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 (here: city of Muenster)

To create new data in the STA the HTTP POST request is used and to read the HTTP GET request. For more information read the documentation: https://docs.ogc.org/is/18-088/18-088.html

Create Data

Create Thing

To insert data the first step is to create a Thing with a HTTP POST request. The URI uses two components which are first the service root URI and second the resource path. Against a local installation of the STA the request looks like this:

http://localhost:8080/52n-sensorthings-webapp/Things

The body of the request is a json document which is shown in the following. It contains a unique identifier, a name and a description for the Thing as well as the properties of the Thing:

{
  "@iot.id": "weather_station_1234",
  "name": "Weather Station 52°North",
  "description": "This is a weather station at the 52°North GmbH office building.",
  "properties": {
    "owner": "52°North GmbH"
  }
}

The response contains the parameters which were inserted by the request as well as a link to the Thing itself, a link to the Datastream, a link to the Location and a link to the HistoricalLocations. For now the links except the selflink do not lead to any data because the data is not yet created.

{
    "@iot.id": "weather_station_1234",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Things(weather_station_1234)",
    "name": "Weather Station 52°North",
    "description": "This is a weather station at the 52°North GmbH office building.",
    "properties": {
        "owner": "52°North GmbH"
    },
    "Datastreams@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Things(weather_station_1234)/Datastreams",
    "Locations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Things(weather_station_1234)/Locations",
    "HistoricalLocations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Things(weather_station_1234)/HistoricalLocations"
}

Create Location

After that a Location needs to be added. In this example the URI for the POST request looks like this:

http://localhost:8080/52n-sensorthings-webapp/Locations

The body of the request contains similiar to the request before the unique identifier, the name and description of the Location. The encoding Type holds the information how the location is encoded and the location describes where the linked Thing is located. The Location is linked to the Thing by using the unique identifier of the Thing:

{
  "@iot.id": "building_127",
  "name": "52°North",
  "description": "office building of the 52°North GmbH",
  "encodingType": "application/vnd.geo+json",
  "location": {
    "type": "Feature",
    "geometry":{
      "type": "Point",
      "coordinates": [7.651968812254194,51.935101100104916]
    }
  },
  "Things": [
      {
          "@iot.id": "weather_station_1234"
      }
  ]
}

The response shows the parameters which were send by the request and the links to the Location itself, the Thing and the HistoricalLocations. The link to the Thing leads to the weather station which was added beforehand.

{
    "@iot.id": "building_127",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Locations(building_127)",
    "name": "52°North",
    "description": "office building of the 52°North GmbH",
    "encodingType": "application/vnd.geo+json",
    "location": {
        "type": "Point",
        "coordinates": [
            7.65196881,
            51.9351011
        ],
        "crs": {
            "type": "name",
            "properties": {
                "name": "EPSG:4326"
            }
        }
    },
    "Things@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Locations(building_127)/Things",
    "HistoricalLocations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Locations(building_127)/HistoricalLocations"
}

Create Sensor

In the next step a Sensor is created. In the following the URI for the POST request is shown:

http://localhost:8080/52n-sensorthings-webapp/Sensors

Again the body of the request contains the unique identifier, the name and the descripition of the entity. The encoding Type shows how the metadata of the Sensor are encoded and the metadata links information about the Sensor:

{
  "@iot.id": "thermometer_1",
  "name": "Thermometer",
  "description": "This thermometer measures the air temperatur",
  "encodingType": "application/pdf",
  "metadata": "http://example.org/Thermometer.pdf"
}

The response holds the parameters of the request, a link to the Sensor itself and a link to the Datastream which is added later.

{
    "@iot.id": "thermometer_1",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Sensors(thermometer_1)",
    "name": "Thermometer",
    "description": "This thermometer measures the air temperatur",
    "encodingType": "application/pdf",
    "metadata": "http://example.org/Thermometer.pdf",
    "Datastreams@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Sensors(thermometer_1)/Datastreams"
}

To present later in the tutorial the filter opitions a second Sensor is added:

{
  "@iot.id": "barometer_2",
  "name": "Barometer",
  "description": "This barometer measures the air pressure",
  "encodingType": "application/pdf",
  "metadata": "http://example.org/Barometer.pdf"
}

Create ObservedProperty

Next an ObservedProperty needs to be created. The URI for the POST request is shown below:

http://localhost:8080/52n-sensorthings-webapp/ObservedProperties

The body of the request contains a unique identifier, a description, a name and a link to the definition of the ObservedProperty:

{
  "@iot.id": "air_temperature",
  "description": "Air temperature is the bulk temperature of the air, not the surface (skin) temperature.",
  "name": "Air Temperature",
  "definition": "http://vocab.nerc.ac.uk/collection/P07/current/CFSN0023/"
}

The parameters of the request are part of the response as well as a link to the ObservedProperty itself and a link to the Datastream which is added in the next step:

{
    "@iot.id": "air_temperature",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/ObservedProperties(air_temperature)",
    "name": "Air Temperature",
    "description": "Air temperature is the bulk temperature of the air, not the surface (skin) temperature.",
    "definition": "http://vocab.nerc.ac.uk/collection/P07/current/CFSN0023/",
    "Datastreams@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/ObservedProperties(air_temperature)/Datastreams"
}

The second Sensor which was added beforehand observes a different phenomenon so a second ObservedProperty needs to be created:

{
  "@iot.id": "air_pressure",
  "description": "Air pressure is the force per unit area which would be exerted when the moving gas molecules of which the air is composed strike a theoretical surface of any orientation.",
  "name": "Air Pressure",
  "definition": "http://vocab.nerc.ac.uk/collection/P07/current/CFSN0015/"
}

Create Datastream

After that a Datastream is created. The URI for the POST request looks like this:

http://localhost:8080/52n-sensorthings-webapp/Datastreams

The body of the Datastream contains as the other entities a unique identifier, a name and a description. Moreover it holds a unit of measurement and an observation Type. A Sensor, an ObservedProperty and a Thing are linked by there unique idenitifier:

{
  "@iot.id": "thermometer_readings_102",
  "name": "Thermometer Readings",
  "description": "This is the reading of a thermometer.",
  "unitOfMeasurement": {
    "name": "degree Celsius",
    "symbol": "°C",
    "definition": "http://unitsofmeasure.org/ucum.html#para-30"
  },
  "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
  "Sensor": {
      "@iot.id": "thermometer_1"
  },
  "ObservedProperty": {
      "@iot.id": "air_temperature"
  },
  "Thing": {
      "@iot.id": "weather_station_1234"
  }
}

Again the response contains the parameters of the request as well as links to the ObservedProperty, the Observations, the Thing and the Sensor:

{
    "@iot.id": "thermometer_readings_102",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)",
    "name": "Thermometer Readings",
    "description": "This is the reading of a thermometer.",
    "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
    "unitOfMeasurement": {
        "name": "degree Celsius",
        "symbol": "°C",
        "definition": "http://unitsofmeasure.org/ucum.html#para-30"
    },
    "observedArea": null,
    "properties": {
        "categoryId": 1,
        "categoryName": "DEFAULT_STA_CATEGORY",
        "categoryDescription": "DEFAULT_STA_CATEGORY"
    },
    "ObservedProperty@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/ObservedProperty",
    "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations",
    "Thing@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Thing",
    "Sensor@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Sensor"
}

For the second Sensor a second Datastream needs to be created.

{
  "@iot.id": "barometer_readings_103",
  "name": "Barometer Readings",
  "description": "This is the reading of a barometer.",
  "unitOfMeasurement": {
    "name": "Pascal",
    "symbol": "Pa",
    "definition": "http://unitsofmeasure.org/ucum.html#para-30"
  },
  "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
  "Sensor": {
      "@iot.id": "barometer_2"
  },
  "ObservedProperty": {
      "@iot.id": "air_pressure"
  },
  "Thing": {
      "@iot.id": "weather_station_1234"
  }
}

Create FeatureOfInterest

Next a FeatureOfInterest needs to be created. The URI for the POST request is shown in the following:

http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest

The body of the FeatureOfInterest contains a unique identifier, a name, a description, an encoding Type for the feature and a description of the feature:

{
  "@iot.id": "muenster",
  "name": "Muenster",
  "description": "This is the city of Muenster.",
  "encodingType": "application/vnd.geo+json",
  "feature": {
    "type": "Feature",
    "geometry":{
      "type": "Point",
      "coordinates": [7.651968812254194,51.935101100104916]
    }
  }
}

The response holds the parameters of the request, a link to the FeatureOfInterest itself and a link to the Observations:

{
    "@iot.id": "muenster",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)",
    "name": "Muenster",
    "description": "This is the city of Muenster.",
    "encodingType": "application/vnd.geo+json",
    "feature": {
        "type": "Point",
        "coordinates": [
            7.65196881,
            51.9351011
        ],
        "crs": {
            "type": "name",
            "properties": {
                "name": "EPSG:4326"
            }
        }
    },
    "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)/Observations"
}

Create Observation

The Observations are created last. The URI of the POST request is presented below:

http://localhost:8080/52n-sensorthings-webapp/Observations

The body of the request contains the phenomenon time which is the time the observation was taken, the result time which is the time the observation was published and the result of the observation. The Observation is linked to the Datastream and FeatureOfInterest by there unique identifier:

{
  "phenomenonTime": "2021-08-17T15:57:53.00+02:00",
  "resultTime": "2021-08-17T15:57:53.00+02:00",
  "result": 16.4,
  "Datastream": {
      "@iot.id": "thermometer_readings_102"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

The response contains the parameters of the request and links to the Observation itself, the Datastream and FeatureOfInterest:

{
    "@iot.id": "656145a4-9124-4af2-ad99-2707e6fb4088",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)",
    "result": "16.4",
    "resultTime": "2021-08-17T13:57:53Z",
    "phenomenonTime": "2021-08-17T13:57:53.000Z",
    "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)/Datastream",
    "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)/FeatureOfInterest"
}

To make it possible to filter the Observations more Observations are added:

{
  "phenomenonTime": "2021-08-17T16:58:16.00+02:00",
  "resultTime": "2021-08-17T16:58:16.00+02:00",
  "result": 16.2,
  "Datastream": {
      "@iot.id": "thermometer_readings_102"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T17:58:08.00+02:00",
  "resultTime": "2021-08-17T17:58:08.00+02:00",
  "result": 15.9,
  "Datastream": {
      "@iot.id": "thermometer_readings_102"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T18:58:22.00+02:00",
  "resultTime": "2021-08-17T18:58:22.00+02:00",
  "result": 15.3,
  "Datastream": {
      "@iot.id": "thermometer_readings_102"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T19:58:13.00+02:00",
  "resultTime": "2021-08-17T19:58:13.00+02:00",
  "result": 14.8,
  "Datastream": {
      "@iot.id": "thermometer_readings_102"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

Also for the second Sensor Observations are added:

{
  "phenomenonTime": "2021-08-17T15:57:53.00+02:00",
  "resultTime": "2021-08-17T15:57:53.00+02:00",
  "result": 101580,
  "Datastream": {
      "@iot.id": "barometer_readings_103"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T16:58:16.00+02:00",
  "resultTime": "2021-08-17T16:58:16.00+02:00",
  "result": 101550,
  "Datastream": {
      "@iot.id": "barometer_readings_103"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T17:58:08.00+02:00",
  "resultTime": "2021-08-17T17:58:08.00+02:00",
  "result": 101590,
  "Datastream": {
      "@iot.id": "barometer_readings_103"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T18:58:22.00+02:00",
  "resultTime": "2021-08-17T18:58:22.00+02:00",
  "result": 101580,
  "Datastream": {
      "@iot.id": "barometer_readings_103"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

{
  "phenomenonTime": "2021-08-17T19:58:13.00+02:00",
  "resultTime": "2021-08-17T19:58:13.00+02:00",
  "result": 101540,
  "Datastream": {
      "@iot.id": "barometer_readings_103"
  },
  "FeatureOfInterest": {
      "@iot.id": "muenster"
  }
}

Read Data

Read Sensor

The data in the STA can be read by sending a HTTP GET request. If a certain Sensor is requested the URI consists out of the service root URI, the resource path and the identifier. For the inserted example data the URI looks like this:

http://localhost:8080/52n-sensorthings-webapp/Sensors(thermometer_1)

The response is a json document. It contains the parameters of the Sensor and links to the Sensor itself and the Datastream:

{
    "@iot.id": "thermometer_1",
    "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Sensors(thermometer_1)",
    "name": "Thermometer",
    "description": "This thermometer measures the air temperatur",
    "encodingType": "application/pdf",
    "metadata": "http://example.org/Thermometer.pdf",
    "Datastreams@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Sensors(thermometer_1)/Datastreams"
}

Read Datastreams with a certain ObservedProperty

All Datastreams which are linked to a certain ObservedProperty can be read by using the URI for the ObservedProperty and expanding it with the ressource path of the linked Datastream. The request for the example is shown below:

http://localhost:8080/52n-sensorthings-webapp/ObservedProperties(air_temperature)/Datastreams

The response document contains all Datastreams which are linked to the certain ObservedProperty (here: one datastream “thermometere_readings_102”):

{
    "@iot.count": 1,
    "value": [
        {
            "@iot.id": "thermometer_readings_102",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)",
            "name": "Thermometer Readings",
            "description": "This is the reading of a thermometer.",
            "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
            "unitOfMeasurement": {
                "name": "degree Celsius",
                "symbol": "°C",
                "definition": "http://unitsofmeasure.org/ucum.html#para-30"
            },
            "observedArea": null,
            "phenomenonTime": "2021-08-17T13:57:53.000Z/2021-08-17T17:58:13.000Z",
            "properties": {
                "categoryId": 1,
                "categoryName": "DEFAULT_STA_CATEGORY",
                "categoryDescription": "DEFAULT_STA_CATEGORY"
            },
            "ObservedProperty@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/ObservedProperty",
            "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations",
            "Thing@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Thing",
            "Sensor@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Sensor"
        }
    ]
}

Read Observations of a certain Datastream

This is another example of requesting all entities which are linked to a different entity. This time all Observations with a certain Datastream are requested:

http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations

The response contains the five Observations which were created for the Datastream:

{
    "@iot.count": 5,
    "value": [
        {
            "@iot.id": "45725aa8-6aab-4861-8b0c-80650e8ec5a0",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(45725aa8-6aab-4861-8b0c-80650e8ec5a0)",
            "result": "15.3000000000",
            "resultTime": "2021-08-17T16:58:22Z",
            "phenomenonTime": "2021-08-17T16:58:22.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(45725aa8-6aab-4861-8b0c-80650e8ec5a0)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(45725aa8-6aab-4861-8b0c-80650e8ec5a0)/FeatureOfInterest"
        },
        {
            "@iot.id": "656145a4-9124-4af2-ad99-2707e6fb4088",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)",
            "result": "16.4000000000",
            "resultTime": "2021-08-17T13:57:53Z",
            "phenomenonTime": "2021-08-17T13:57:53.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(656145a4-9124-4af2-ad99-2707e6fb4088)/FeatureOfInterest"
        },
        {
            "@iot.id": "cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)",
            "result": "15.9000000000",
            "resultTime": "2021-08-17T15:58:08Z",
            "phenomenonTime": "2021-08-17T15:58:08.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)/FeatureOfInterest"
        },
        {
            "@iot.id": "cf46d95a-6372-45d1-a201-619d386074c0",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)",
            "result": "16.2000000000",
            "resultTime": "2021-08-17T14:58:16Z",
            "phenomenonTime": "2021-08-17T14:58:16.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)/FeatureOfInterest"
        },
        {
            "@iot.id": "fd612941-cb7e-4f0d-997f-13b684e178c0",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(fd612941-cb7e-4f0d-997f-13b684e178c0)",
            "result": "14.8000000000",
            "resultTime": "2021-08-17T17:58:13Z",
            "phenomenonTime": "2021-08-17T17:58:13.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(fd612941-cb7e-4f0d-997f-13b684e178c0)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(fd612941-cb7e-4f0d-997f-13b684e178c0)/FeatureOfInterest"
        }
    ]
}

Read Observations filtered by resultTime

This example shows how to add a filter to the request. It is equal to the example before, but this time a parameter is added to the GET request to filter the Observations by the result time:

http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations?$filter=resultTime ge 2021-08-17T14:00:00Z and resultTime le 2021-08-17T16:00:00Z

The response document only contains Observations which were published in the requested time period:

{
    "@iot.count": 2,
    "value": [
        {
            "@iot.id": "cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)",
            "result": "15.9000000000",
            "resultTime": "2021-08-17T15:58:08Z",
            "phenomenonTime": "2021-08-17T15:58:08.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)/FeatureOfInterest"
        },
        {
            "@iot.id": "cf46d95a-6372-45d1-a201-619d386074c0",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)",
            "result": "16.2000000000",
            "resultTime": "2021-08-17T14:58:16Z",
            "phenomenonTime": "2021-08-17T14:58:16.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)/Datastream",
            "FeatureOfInterest@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cf46d95a-6372-45d1-a201-619d386074c0)/FeatureOfInterest"
        }
    ]
}

Read Datastreams with a certain FeatureOfInterest

In this example is shown how to request all Datastreams with the same FeatureOfInterest. This request is more complicated because the FeatureOfInterest is only indirectly linked to the Datastream by the Observations. For this request a filter needs to be used:

http://localhost:8080/52n-sensorthings-webapp/Datastreams?$filter=Observations/FeatureOfInterest/id eq ‘muenster’

The response holds both Datastreams which were created because there Observations are linked to the same FeatureOfInterest:

{
    "@iot.count": 2,
    "value": [
        {
            "@iot.id": "barometer_readings_103",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(barometer_readings_103)",
            "name": "Barometer Readings",
            "description": "This is the reading of a barometer.",
            "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
            "unitOfMeasurement": {
                "name": "Pascal",
                "symbol": "Pa",
                "definition": "http://unitsofmeasure.org/ucum.html#para-30"
            },
            "observedArea": null,
            "phenomenonTime": "2021-08-17T13:57:53.000Z/2021-08-17T17:58:13.000Z",
            "properties": {
                "categoryId": 1,
                "categoryName": "DEFAULT_STA_CATEGORY",
                "categoryDescription": "DEFAULT_STA_CATEGORY"
            },
            "ObservedProperty@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(barometer_readings_103)/ObservedProperty",
            "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(barometer_readings_103)/Observations",
            "Thing@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(barometer_readings_103)/Thing",
            "Sensor@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(barometer_readings_103)/Sensor"
        },
        {
            "@iot.id": "thermometer_readings_102",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)",
            "name": "Thermometer Readings",
            "description": "This is the reading of a thermometer.",
            "observationType": "http://www.opengis.net/def/observationType/OGC-OM/2.0/OM_Measurement",
            "unitOfMeasurement": {
                "name": "degree Celsius",
                "symbol": "°C",
                "definition": "http://unitsofmeasure.org/ucum.html#para-30"
            },
            "observedArea": null,
            "phenomenonTime": "2021-08-17T13:57:53.000Z/2021-08-17T17:58:13.000Z",
            "properties": {
                "categoryId": 1,
                "categoryName": "DEFAULT_STA_CATEGORY",
                "categoryDescription": "DEFAULT_STA_CATEGORY"
            },
            "ObservedProperty@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/ObservedProperty",
            "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations",
            "Thing@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Thing",
            "Sensor@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Sensor"
        }
    ]
}

Read Observations with expanded FeatureOfInterest

In this example is shown how to structure the response document. In this request again all Observations of a certain Datastream are requested. But this time parameters are added to the GET request to order the observations ascending by the phenomenon time, to request the top twoObservations, to skip the first two Observations and to expand the linked FeatureOfInterest:

http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations?$orderby=phenomenonTime asc&$top=2&$skip=2&$expand=FeatureOfInterest

The response document contains the requested Observations:

{
    "@iot.count": 5,
    "@iot.nextLink": "http://localhost:8080/52n-sensorthings-webapp/Datastreams(thermometer_readings_102)/Observations?$top=2&$orderby=phenomenonTime asc&$expand=FeatureOfInterest($top=100)&$skip=4",
    "value": [
        {
            "@iot.id": "cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)",
            "result": "15.9000000000",
            "resultTime": "2021-08-17T15:58:08Z",
            "phenomenonTime": "2021-08-17T15:58:08.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(cb2c0cc6-c9c8-4e47-a665-9029a0ff6ac4)/Datastream",
            "FeatureOfInterest": {
                "@iot.id": "muenster",
                "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)",
                "name": "Muenster",
                "description": "This is the city of Muenster.",
                "encodingType": "application/vnd.geo+json",
                "feature": {
                    "type": "Point",
                    "coordinates": [
                        7.65196881,
                        51.9351011
                    ],
                    "crs": {
                        "type": "name",
                        "properties": {
                            "name": "EPSG:4326"
                        }
                    }
                },
                "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)/Observations"
            }
        },
        {
            "@iot.id": "45725aa8-6aab-4861-8b0c-80650e8ec5a0",
            "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(45725aa8-6aab-4861-8b0c-80650e8ec5a0)",
            "result": "15.3000000000",
            "resultTime": "2021-08-17T16:58:22Z",
            "phenomenonTime": "2021-08-17T16:58:22.000Z",
            "Datastream@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/Observations(45725aa8-6aab-4861-8b0c-80650e8ec5a0)/Datastream",
            "FeatureOfInterest": {
                "@iot.id": "muenster",
                "@iot.selfLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)",
                "name": "Muenster",
                "description": "This is the city of Muenster.",
                "encodingType": "application/vnd.geo+json",
                "feature": {
                    "type": "Point",
                    "coordinates": [
                        7.65196881,
                        51.9351011
                    ],
                    "crs": {
                        "type": "name",
                        "properties": {
                            "name": "EPSG:4326"
                        }
                    }
                },
                "Observations@iot.navigationLink": "http://localhost:8080/52n-sensorthings-webapp/FeaturesOfInterest(muenster)/Observations"
            }
        }
    ]
}