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此库旨在在不同的单位系统之间进行转换，以及将公制值转换为它们的词头。

示例

单位转换

<?php
use Drieschel\UnitsOfMeasurement\SiPrefixConverter;
use Drieschel\UnitsOfMeasurement\UnitCollection;
use Drieschel\UnitsOfMeasurement\UnitConverter;

// Own units and/or prefixes can be used by providing them in the constructor. Both is optional.
$units = UnitCollection::createAllUnits();
$siPrefixes = SiPrefixCollection::create();
$unitConverter = new UnitConverter($units, $siPrefixes);

// Converting miles to kilometre ($converted = 20.1168).
$converted = $unitConverter->convertBySymbol('mi', 'km', 12.5);

词头转换

假设你有一个可以处理微克（µg）值的程序，但提供的数据是在千克（kg）中。数据可以通过SI词头转换组件轻松地从千克转换为微克。

<?php
use Drieschel\UnitsOfMeasurement\SiPrefixCollection;
use Drieschel\UnitsOfMeasurement\SiPrefixConverter;
use Drieschel\UnitsOfMeasurement\UnitCollection;

// Own units and/or prefixes can be used by providing them in the constructor. Both is optional.
$units = UnitCollection::createAllUnits();
$siPrefixes = SiPrefixCollection::create();
$prefixConverter = new SiPrefixConverter($units, $siPrefixes);

// Note: The second argument from the "convertByUnitSymbol" method is the prefix symbol.

// Converting litre to centilitre ($converted = 37.5).
$centilitre = $prefixConverter->convertByUnitSymbol('L', 'c', 3.75);

// Converting microgram to milligram ($milligram = 0.0021).
$milligram = $prefixConverter->convertByUnitSymbol('µg', 'm', 2.1);

// Note: The empty string ('') is the prefix symbol for 1E0 (1.).
// Converting kilotonne to tonne ($tonne = 230.).
$tonne = $prefixConverter->convertByUnitSymbol('kt', '', 0.23);

单位

可以通过单位集合的静态工厂方法创建单位集合。

<?php
use Drieschel\UnitsOfMeasurement\UnitCollection;
use Drieschel\UnitsOfMeasurement\PhysicalQuantityCollection;

// Create all defined units. If the US Customary system is preferred over the
// Imperial unit system, then the second (optional) argument has to be set to true.    
// It doesn't matter which system is preferred. Both unit versions (Imperial and USC)
// will be created every time, the preferred version just has no unit system prefix 
// in the symbol.
$physicalQuantities = PhysicalQuantityCollection::create();
$preferUsc = true;
$units = UnitCollection::createAllUnits($physicalQuantities, $preferUsc);

// A unit can get accessed by array notation or by get method.
// This is the US preferred version, because the $preferUsc flag was set to true.
$usGallon = $units['gal'];
$usGallon = $units->get('gal');
$impGallon = $units['imp gal'];
$impGallon = $units->get('imp gal');

// Create SI base units only.
$siBaseUnits = UnitCollection::createSiBaseUnits($physicalQuantities);

// Create SI derived units only.
$siDerivedUnits = UnitCollection::createSiDerivedUnits($physicalQuantities, $siBaseUnits);

// Create non SI units only.
// The preferred non metric unit system can be chosen as in the "createAllUnits" method call.
$nonSiUnits = UnitCollection::createNonSiUnits($physicalQuantities, $siBaseUnits, $preferUsc);

物理量

物理量集合可以通过多维数组（只读）访问，以获取特定的单位或物理量。

<?php
use Drieschel\UnitsOfMeasurement\PhysicalQuantity;
use Drieschel\UnitsOfMeasurement\PhysicalQuantityCollection;
use Drieschel\UnitsOfMeasurement\SiBaseUnit;
use Drieschel\UnitsOfMeasurement\NonSiUnit;

// The $createUnits parameter can be set to true for creating all units at once.
// The $preferUsc can be set to true if the US Customary unit system is preferred 
// over the Imperial unit system.
$createUnits = true;
$preferUsc = true;
$physicalQuantities = PhysicalQuantityCollection::create($createUnits, $preferUsc);

/** @var SiBaseUnit $metre */
$metre = $physicalQuantities['l']['m'];
$metre = $physicalQuantities->get('l')->get('m');

/** @var NonSiUnit $litre */
$litre = $physicalQuantities['V']['L'];

/** @var PhysicalQuantity $mass */
$mass = $physicalQuantities['m'];