System Description

Observation Entity

Information regarding a single measurement of a sensor is stored in a JSON-based observation entity. Whenever a request is made to a sensor, it must be embedded into an observation entity along with meta information like name and target of the observation, name of the serial port, regular expression pattern of the sensor’s raw response, and so on.

All observations that will be send to a sensor are stored prior in a configuration file in JSON format. OpenADMS Node reads the configuration file and processes the observations according to their properties.

Observation entities can be enhanced by adding optional key-value pairs. But most elements in an observation entity are mandatory. The following basic object stores the finished observation getValues with two requests getTemperature and getPressure of the STS DTM meteorological sensor. The observation was send to the modules com1, preProcessor, and fileExporter.

{
  "name": "getValues",
  "type": "observation",
  "description": "get sensor values (temperature, pressure)",
  "sensorName": "stsDTM",
  "timestamp": "2017-04-05T21:48:00.805527",
  "target": "TempPress",
  "id": "6dc84c06018043ba84ac90636ed0f677",
  "pid": "6600055d61ce4d8698f77596e436785f",
  "nid": "21bcf8c16a664b17bbc9cd4221fd8541",
  "enabled": true,
  "onetime": false,
  "receivers": [
    "com1",
    "preProcessor",
    "fileExporter"
  ],
  "nextReceiver": 4,
  "portName": "COM1",
  "passiveMode": false,
  "requestsOrder": [
    "getTemperature",
    "getPressure"
  ],
  "requestSets": {
    "getTemperature": {
      "enabled": true,
      "request": "TEMP ?\r",
      "response": ">+23.1",
      "responseDelimiter": "\r",
      "responsePattern": "(?P<temperature>[+-]?\\d+\\.+\\d)",
      "sleepTime": 1.0,
      "timeout": 1.0
    },
    "getPressure": {
      "enabled": true,
      "request": "PRES ?\r",
      "response": ">+1011.3",
      "responseDelimiter": "\r",
      "responsePattern": "(?P<pressure>[+-]?\\d+\\.+\\d)",
      "sleepTime": 1.0,
      "timeout": 1.0
    }
  },
  "responseSets": {
    "temperature": {
      "type": "float",
      "unit": "C",
      "value": "23.1"
    },
    "pressure": {
      "type": "float",
      "unit": "mbar",
      "value": "1011.3"
    }
  },
  "sleepTime": 20.0
}

The single elements of this observation entity are explained below.

Name	Data Type	Description
description	String	Short description of the observation (optional).
enabled	Boolean	Condition of the observation (enabled/disabled).
id	String	ID of the observation (UUID4 hex only).
name	String	Name of the observation.
nextReceiver	Integer	Index of the next receiver (0 … n).
nid	String	Sensor node ID (UUID4 hex).
onetime	Boolean	If true, observation will be send one time only.
passiveMode	Boolean	If true, serial port communication is passive only (depends on sensor).
portName	String	Name of the serial port (will be added automatically).
pid	String	Project ID (UUID4 hex).
receivers	Array	Array of modules the observation will be send to sequentially.
requestSets	Object	Requests to the sensor, response patterns, etc.
requestsOrder	Array	Defines the order of the requests.
responseSets	Object	Response units, types, and values.
sensorName	String	Name of the sensor (will be added by the scheduler).
sensorType	String	Type of sensor (e.g., total station, GNSS receiver, …).
sleepTime	Float	Time in seconds to wait before the next observation.
target	String	Target name of the observation (e.g., point name, target location).
timestamp	String	Time stamp of the observation (UTC in ISO 8601).
type	String	Name of data type (always observation).