Metrics in measurements

Metric

A metric brings together several notions into a reportable quantity

• What is sensed (e.g. PM2.5, NO2, Wind)
• A measurable trait of above (e.g. Mass concentration, Speed, Compass direction)
• The aggregation applied (e.g. No aggregation, 1-Hour mean, 24-hour mean)
• The units or pollution index applied (e.g. μg/m³, ppb, US EPA AQI)

Attributes within a metric

Some metrics have ready-to-use values directly from the sensor. No further processing occurs. Examples are temperature, relative humidity and wind. Other metrics have raw data that can benefit from further processing in the cloud. We call these metrics cloud-calibrated. Examples are PM2.5 and NO2.

• Direct from sensor: raw and value are the same
• Cloud-calibrated: raw is from sensor, value is cloud-calibrated

This means you can consistently access the same attribute regardless of metric, with value being most appropriate for visualization and analysis. Keep an eye on the status field though (see Status table below). If the response is a JSON format, the attributes are in an object, like this (where the word metric is a name from the metrics dictionary)

   ...
   "metric": {
       "raw":
       "value":
       "status":
   }
   ...

If the response is tabular, like CSV or Parquet, the attributes are dot-notation column headers like this:

    ..., metric.raw, metric.value, metric.status, ...

Attribute details

Clarity Node - metric is direct from sensor

attribute	description
raw	The sensed value direct from the device
value	Same as raw
status	sensor-ready

Clarity Node - metric can be cloud-calibratred

attribute	description
raw	The sensed value direct from the device
value	The calibration result. null if calibration has not occurred
status	see table below

status for cloud-calibrated metrics

status	description
calibration-missing	No calibrated value because a calibration was not assigned to the device durign the last processing
calibration-processing	Calibration is in process
calibrated-reprocessing	A calibrated value exists and a newer calibration is in process
calibration-error	Calibration failed for the data coming from the device
calibrated-ready	Calibration has completed
calibrated-mixed	Only for aggregations: The individual samples in the aggregation period do not all have the same calibration-status. To understand the mix of statuses, fetch the individual measurements

For reference sites

attribute	description
raw	null
value	The value direct from the reference provider
status	reference-ready

Output frequency

The fields a measurement contains depend on the output frequency of the measurement. Your request to retrieve measurements includes an outputFrequency. Tables below list all the possible metrics, by output frequency.

Output frequency	type of measurement
minute	An individual sample, received from a deployed device, containing everything that device sends.
hour	An hourly aggregation.
day	A daily aggregation, where a new day is defined in UTC time

Limit what gets returned

By default, each measurement will be reported with many metrics. Sometimes, you may want to control which metrics within each measurement are returned. You can do this with the metricsSelect parameter. Here are a few examples. See Metrics selection for more details.

Selector	example of	returns in the measurement
only :pm	Colon : category matching	metrics in the PM category
only no2*aqi	Star * pattern matching	metrics whose name starts with no2 and ends with aqi
all - :blackcarbon	Removal - from set	all metrics minus any in the black carbon category