base(3)
NAME
Convert::Units::Base - base object for performing unit
conversions
DESCRIPTION
The Units package is a collection of modules for parsing
strings with unit measurements (such as "12pt" or "3
meters") and converting them to some other unit (such as
"picas" or "inches").
It uses a base package (Units::Base) which does the dirty
work. Other modules define what units they handle and how
they are related.
Why a Separate Module?
It is intentionally distinct from the Math::Units module.
Why? The Math::Units module implies that unit conversions
are exact, with one-to-one relationships. This is fine
for scientific work. It's even fine for some general pur
pose/real-world uses (such as converting Fehrenheight to
Celcius).
Real-world measurement systems are conflicting. For
instance, a "point" in typography is equivalent to 1/72
inch, according to PostScript specs and common usage.
Other type systems consider it 1/72.27 inch, or 0.01383
inches, or 0.0148 inches. Outside of that context, a
point may be 1/120 or 1/144 inch.
Common notations and abbreviations also depend on context.
Does "12 pt" mean "12 point", "12 parts" or "12 pints"?
Even without conflicts in the definition of a particular
unit, there's no need to convert point sizes for fonts
into miles or light-years. Typesetters, surveyors and
astronomers user different scales as well as systems.
People do not think like computers
Not everyone uses the metric system.
And even less people say things like "5.25 feet". Often
it's "5 feet, 3 inches" or "5 1/4 feet".
Despite having ten fingers and toes, people don't think in
tens. They think in twos, threes, fours, twelves, and six
teens. And sometimes they use fractional measurements like
quarter-inches, sixteenths-of-an-inch, or half-pints.
The purpose of this module is to allow people to use the
measurement systems they are familiar with, and that is
appropriate to what they are doing.
Rationale
The Units:: hierarchy is an attempt to keep measurement
systems in distinct classes. Thus one can have modules for
converting between typography units (points, picas) dis
tinct from common units of length (or area, temperature,
etc.), specialized units (for Astronomy, Chemistry,
Physics, Textiles, Winery, Navigation, etc.) or even
traditional or regional systems (Japanese, Chinese, Egyp
tian, archaic systems, etc.) and to keep conflicting mea
surement systems distinct.
Release Notes
- The current distribution contains the following packages:
- Convert::Units::
::Base - a base module that does all of the - work
::Length - a module for converting units of - length
::Temperature - a module for converting units of tem - perature
::Type - a module for converting units of type - Units::Base by itself does nothing. Another module needs
to use it to create definitions of what units of measure
ment it handles and how they are related to each other
(ie, 1 m = 100 cm). - The base unit also allows for synonym and abbreviations to
be defined. - It also allows common "multiples" to be defined, so that
it can handle things like "18 half-points" or "6 dozen
feet" or even convert millimters to "sixteenths of an
inch". (It does not yet handle Greek prefixes like centior mega- ... those will have to be manually defined.) - Known Issues
- The current release should be considered "beta" until fur
ther testing and refinements have been made. Then again,
maybe "alpha" is more accurate. - The current version does not yet handle fractions such as
"1/2 in". It should handle decimals such as "0.5 in". - Relationships have been rewritten to be handle A(x+b) as
well Ax. They may be redone in the future to handle more
complex relationships, if the need arises. - Unit names much be defined as all lowercase, since strings
are munged with lc() before processing. In other words, if
you define a unit name as "F" or "Fahrenheight" you won't
be able to use it. - Future Enhancements
- Aside from bug fixes, optimizations, and making the string
parsing conform more to the "manifesto" above, obvious
additions would be modules for converting between units of
area, volume, weight... (although if Math::Units does what you need, use that instead.) - An example hierarchy for future modules:
Convert::Units::
::Length - general measures of length
::Area
::Pressure
::Volume- Convert::Units::Length
::Chinese - specialized regional/traditional - systems
::English - Convert::Units::Astronomy
::Length - or Distance...? - Modules should share a common unit (preferably metric) to
allow for conversions.
REQUIRED MODULES
Carp
SEE ALSO
Units::Length, Units::Temperature and Units::Type modules,
which demonstrate how Units::Base is used.
AUTHOR
Robert Rothenberg <wlkngowl@unix.asb.com>
LICENSE
- Copyright (c) 1999-2000 Robert Rothenberg. All rights
reserved. This program is free software; you can redis
tribute it and/or modify it under the same terms as Perl
itself.