It is in VSS possible for signals to specify a unit of measurement from a list of predefined data unit types.
For most signals in the VSS standard catalog, a data unit type has been selected. A typical example is Vehicle.Speed, as shown below.
Vehicle.Speed:
datatype: float
type: sensor
unit: km/h
description: Vehicle speed.
The ambition when selecting data unit types for signals in VSS standard catalog has been to use either a unit based on SI-units,
or a unit commonly used within the vehicle industry. For the Vehicle.Speed example above this means that km/h has been selected,
even if m/s from an SI-perspective would have been a better choice.
It must be noted that the selected unit does not imply that the value of Vehicle.Speed always needs to be sent or visualized
as km/h (with float as datatype). A user interface or API may show or request vehicle speed in any unit it likes,
and a transport protocol may send speed in another unit, possibly also involving scaling and offset.
But in protocols not explicitly specifying data unit types (like VISS)
it is expected that Vehicle.Speed is sent and received as km/h (without scaling or offset).
In some cases it is natural to omit the data unit type. This concerns typically signals where data type string is used,
but also signals where the value just represents a number, like in the example below:
Vehicle.Cabin.DoorCount:
datatype: uint8
type: attribute
default: 4
description: Number of doors in vehicle.
VSS supports percent as data unit type, typically with 0 to 100% as the allowed range.
In some cases, the definition on how to calculate the signal value is obvious, like for Vehicle.Powertrain.FuelSystem.Level
below. It is likely that all VSS users will calculate fuel level in the same way, i.e. the meaning of a fuel level of 50%
is well agreed, the liters of fuel in the tank is exactly 50% of nominal capacity.
Vehicle.Powertrain.FuelSystem.Level:
datatype: uint8
type: sensor
unit: percent
min: 0
max: 100
description: Level in fuel tank as percent of capacity. 0 = empty. 100 = full.
In other cases, the formula for calculating the signal is not obvious and is not specified in VSS. A typical example is shown below for clutch wear. While most VSS users likely can agree that a brand new clutch shall have 0 as “ClutchWear”, the exact formula for calculating clutch wear for a used clutch will likely be vehicle specific. Some vehicles might monitor actual wear, others might estimate it based on vehicle usage. This is in VSS called a logical range, a VSS user knows what range to use but are free to define the formula for calculating the value. Values from different vehicles (of different make/model) can not always be compared, as the formula used for calculation may differ.
Vehicle.Powertrain.Transmission.ClutchWear:
datatype: uint8
type: sensor
unit: percent
max: 100
description: Clutch wear as percent. 0 = no wear. 100 = worn.
This list composed with definition according to International Units (SI) and few automotive specific units: Specification, Wikipedia
| Unit type | Domain | Description |
|---|---|---|
| mm | Distance | Distance measured in millimeters |
| cm | Distance | Distance measured in centimeters |
| m | Distance | Distance measured in meters |
| km | Distance | Distance measured in kilometers |
| inch | Distance | Distance measured in inches |
| km/h | Speed | Speed measured in kilometers per hours |
| m/s | Speed | Speed measured in meters per second |
| m/s^2 | Acceleration | Acceleration measured in meters per second squared |
| cm/s^2 | Acceleration | Acceleration measured in centimeters per second squared |
| ml | Volume | Volume measured in milliliters |
| l | Volume | Volume measured in liters |
| cm^3 | Volume | Volume measured in cubic centimeters |
| celsius | Temperature | Temperature measured in degree celsius |
| degrees | Angle | Angle measured in degrees |
| degrees/s | Angular Speed | Angular speed measured in degrees per second |
| W | Power | Power measured in watts |
| kW | Power | Power measured in kilowatts |
| PS | Power | Power measured in horsepower |
| kWh | Energy Consumption | Energy consumption measured in kilowatt hours |
| g | Weight | Mass measured in grams |
| kg | Weight | Mass measured in kilograms |
| lbs | Weight | Mass measured in pounds |
| V | Electric Potential | Electric potential measured in volts |
| A | Electric Current | Electric current measured in amperes |
| Ah | Electric Charge | Electric charge measured in ampere hours |
| ms | Time | Time measured in milliseconds |
| s | Time | Time measured in seconds |
| min | Time | Time measured in minutes |
| h | Time | Time measured in hours |
| day | Time | Time measured in days |
| weeks | Time | Time measured in weeks |
| months | Time | Time measured in months |
| years | Time | Time measured in years |
| UNIX Timestamp | Time | Unix time is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, excluding leap seconds. |
| mbar | Pressure | Pressure measured in millibars |
| Pa | Pressure | Pressure measured in pascal |
| kPa | Pressure | Pressure measured in kilopascal |
| stars | Rating | Rating measured in stars |
| g/s | Mass per time | Mass per time measured in grams per second |
| g/km | Mass per distance | Mass per distance measured in grams per kilometers |
| kWh/100km | Energy Consumption per distance | Energy consumption per distance measured in kilowatt hours per 100 kilometers |
| ml/100km | Volume per distance | Volume per distance measured in milliliters per 100 kilometers |
| l/100km | Volume per distance | Volume per distance measured in liters per 100 kilometers |
| l/h | Flow | Flow measured in liters per hour |
| mpg | Distance per Volume | Distance per volume measured in miles per gallon |
| N | Force | Force measured in newton |
| Nm | Torque | Torque measured in newton meters |
| rpm | Rotational Speed | Rotational speed measured in revolutions per minute |
| Hz | Frequency | Frequency measured in hertz |
| ratio | Relation | Relation measured as ratio |
| percent | Relation | Relation measured in percent |
| … | … | … |
VSS-Tools require that a unit file is available when transforming *.vspec files.
It can be specified by the -u parameter, and if not given the tools will search for a file units.yaml
in the same directory as the root *.vspec file.
The VSS standard catalog is based on units.yaml, i.e. only units from that file can be used.