uom

A lightweight Ruby library for representing units of physical measure and quantities represented in those units.

Usage

1. Vendor this code and load up lib/ in your $:.
2. require 'uom'.
3. See below.

Units and Quantities

This library supports simple units, such as "m" (metre), as well as compound units, such as "lb in^-2" (pounds per square inch). Unit definitions are in lib/uom/unit_definitions.rb.

Measurable quantities are represented by Uom::Quantity:

>> Uom::Quantity.new(15, 'cm')
=> 15 cm

The Uom::Quantity#convert_to(units) method converts units:

>> Uom::Quantity.new(15, 'cm').convert_to(:ft)
=> 0.492125985 ft

Ruby Core Extensions

uom extends Numeric, so you can generate Uom::Quantity objects like 1.cm or 3.2.ft.

You can also use in_someunit to convert from one unit to another. For example:

>> 15.ft.in_cm
=> 457.199999305056

>> 32.degF.in_K
=> 273.15

Rails / ActiveRecord Integration

uom can be installed as a Rails plugin. It will automatically load its ActiveRecord extensions, so you can integrate with Uom::Quantity like this:

class Person < ActiveRecord::Base
  # default columns: height_amount:numeric and height_units:text
  uom :height
  
  # You can change them like this:
  uom :weight, :scalar_attribute => 'weight',
               :units_attribute  => 'units_of_weight'
end

Person.new :height => 173.cm, :weight => 75.kg

If you're not using Rails, you can load the ActiveRecord extensions by requiring 'uom/active_record'.

To do / Quirks

• Time durations are not supported, for want of an elegant way to represent them. Perhaps we should wrap ActiveSupport::Duration?

• uom currently assumes that all non-temperature units are multiplicative, i.e., have no constant offset involved and can therefore be represented as a constant factor times a base unit. This should be genericized.

• Add arithmetic support for Uom::Quantity.

Authors

• Brad Ediger (brad.ediger at madriska.com)
• Gregory Brown (gregory.t.brown at gmail.com)