Unit Conversion¶

This section describes how HortiView deals with units and unit conversions throughout the platform.

Rationale¶

Thanks to decades of standardization, converting between different quantities is simple. Converting between the metric and imperial system is not difficult either. Consistent use of units in an application, on the other hand, is a tricky business. Especially when multiple software vendors contribute to the platform.

The ability to consistently render values for different quantities, such as length, area, temperature etc. can be complex, given the multitude of combinations of quantity, unit system and the actual value used. For example, when the backend returns the value 42 for an area without specifying the unit associated with that value, it will be difficult to work with, even if we know the context we are operating in.

In HortiView we want to make life as easy as possible for developers and help eliminate conversion errors. Therefore we defined 3 principles to support our goal:

1. The HortiView Backend will store and return values for specific quantities using SI base units and SI coherent derived units.
2. Organizations can define what quantities should be converted to specific units.
3. The frontend is responsible for conversion since vendors know the context their modules operate in best.

Unit Systems¶

In HortiView we store values in SI base units and SI coherent derived units, with one exception: temperature is stored in Celsius (C) instead of the thermodynamic quantity Kelvin (K).

By default, we use the following SI base units:

Conversion Process¶

Since the HortiView backend is agnostic about the target unit a value is about to be converted to, it will always return values in standard units derived from SI base units. For example, if an entity has the property area it will respond to requests with the unit sqm (square meters):

{
    "measurement" {
        "area": "42",
        "unit": "sqm"
    }
}

The following figure illustrates the process:

Examples¶

Since the frontend is responsible for the conversion, HortiView offers a simple interface to interact with the conversion library. The library is a wrapper for convert.js, a well known and mature unit conversion library for frontend developers.

yarn add hv-convert

Simple Operations¶

import c7 from "hv-convert";
import measures as m from "hv-convert";

c7(5, m.kilometers).to(m.miles);     // -> 
c7(12, m.kilograms).to(m.pounds);    // ->
c7(81, m.gallons).to(m.liters);      // ->
c7(10, m.atmospheres).to(m.kPa);     // ->
c7(451, m.fahrenheit).to(m.celsius); // ->
c7(360, m.seconds).to(m.minutes);    // -> 6

Mapping Between Unit Systems¶

By convention, HortiView stores values in SI units using the metric system. Depending on the user preferences the mapping to the imperial system is possible, but must be performed by the frontend.

<< Describe how we can read user prefs and convert to metric/imperial automatically>>

Overview of SI Base Units¶