Aliases

COSMOS aliases are an extension of the COSMOS Namespace that allows the mapping of a new user defined name to any existing Name, or Equation, in the Namespace. These can be used for such things as providing more user friendly names, or mapping an external namespace in to COSMOS. The following example shows a typical use of COSMOS aliases. There is a self contained example that can be run using Qt creator from the folder <cosmos-source>/core/tutorials/namespace/aliases and using the file alias.cpp.

Example

Objective: convert the IMU temperature data from degrees Celcius to Kelvin. This actually could be handled differently by unit conversion but the purpose here is to demonstrate the use of equations in COSMOS.

The base unit in COSMOS for temperatures is Kelvin so lets define the equation to convert to from Kelvin to Celcius

The namespace variable for the imu tempperature in this case is "device_imu_temp_000", knowing this we can add equation to namespace. The equation will be formed as a JSON string

(\"device_imu_temp_000\" - 273.15)

To simplify the use of this equation we use an alias such as

"imuTempCelcius"

The code to handle COSMOS namespace aliases and equations can be found in jsonlib.cpp. The relevant functions for aliases are json_addentry and json_get_double. For equations the relevant functions are json_equation and json_equation_map.