UDUnits

Installation

Inside the Julia shell, you can download and install the package by issuing:

using Pkg
Pkg.add("UDUnits")

Latest development version

If you want to try the latest development version, you can do this with the following commands:

using Pkg
Pkg.add(PackageSpec(url="https://github.com/Alexander-Barth/UDUnits.jl", rev="master"))
Pkg.build("UDUnits")

Loading the module

The first step is to load the module UDUnits and to initialize the unit system sys which correspond to the SI unit system.

using UDUnits
sys = System()

Units

The unit objects can be created for m and cm using either their symbol or their full name by indexing the sys object as if sys is a dictionary.

m = sys["meter"]
cm = sys["cm"]

Similarily to a dictionary, the function haskey is defined to determine if a unit is valid:

haskey(sys,"μm") # returns true since UDUnits knows about micrometers

Derived units

Units can be derived using the usual mathemical operators. Of course, m_per_s could have been also create simply by using sys["m/s"].

m = sys["m"]
km = sys["km"]
s = sys["s"]
h = sys["h"]
m_per_s = m/s
km_per_h = km/h

Converting data

The function areconvertible returns true if two units are convertible:

@show areconvertible(m_per_s,km_per_h)

To convert units, create a converter object and then apply the object to some data.

conv = Converter(m_per_s,km_per_h)
speed_in_m_per_s = 100.
speed_in_km_per_h = conv(speed_in_m_per_s)

The dot syntax can be used for an array as input:

speed_in_m_per_s = [100.,110.,120.]
speed_in_km_per_h = conv.(speed_in_m_per_s)

Windows

I did not succeed to install UDUnits.jl on Windows using the package manager Conda. One way to make it work on Windows is to bypass Conda:

• extract udunits2.dll and all xml files from https://anaconda.org/conda-forge/udunits2/2.2.23/download/win-64/udunits2-2.2.23-vc9_1.tar.bz2

• expat.dll from https://anaconda.org/conda-forge/expat/2.1.0/download/win-64/expat-2.1.0-vc9_1.tar.bz2

• place all these files in the deps folder of UDUnits (i.e. the output of joinpath(Pkg.dir("UDUnits"),"deps"))

• run

Pkg.build("UDUnits")

• before any call to using UDUnits or import UDUnits, set the following variable:

ENV["UDUNITS2_XML_PATH"] = joinpath(Pkg.dir("UDUnits"),"deps","udunits2.xml")

Alternatives

• UDUnits.jl

Resources

• Documentation of the C-library