Dear UDUNITS user,

Version 2 of the UDUNITS package is now available from the UDUNITS
homepage at <http://www.unidata.ucar.edu/software/udunits/>.

The UDUNITS-2 package differs from the previous UDUNITS package in the
following ways:

    Support for non-ASCII characters. The original UDUNITS package only
    supports the ASCII character set. The UDUNITS-2 package supports
    the following character sets: ASCII, ISO 8859-1 (Latin 1), and the
    UTF-8 encoding of ISO 10646 (Unicode). This means that unit string
    specifications like "µ°F·Ω⁻¹" are now supported (your viewer
    must support UTF-8 to display this string correctly).

    Support for logarithmic units. The unit string specification
    "0.1 lg(re 1 mW)" specifies a deciBel unit with a one milliwatt
    reference level.  Meteorologists should note that the unit "dBZ"
    (i.e., "0.1 lg(re um^3)") is now supported.

    Persistent value converters. It is now possible to obtain a converter
    data-object, which can be used to convert numeric values in one
    unit to numeric values in another, compatible unit. The values can
    be float, double, or one-dimensional arrays of floats or doubles.

    Improved API. Due to the above changes, it was not possible to keep
    the application programming interface of the original UDUNITS
    package.  Beginning with version 2.1.0, however, the package
    contains a thin UDUNITS API to the UDUNITS-2 library, so code
    written to the original API can simply be recompiled and relinked
    against the new package.  Because the original UDUNITS API uses the
    "utUnit" data-structure and the UDUNITS-2 API uses pointers to
    "ut_unit" data-structures, a small memory-leak is possible in code
    that creates many units.  This leak can be avoided by calling the
    new method utFree(utUnit*) when the unit is no longer needed.

    XML unit database. The unit database is encoded using human-readable
    XML rather than a custom format. The XML parser included in the
    package supports an <import> element to allow easy and convenient
    customization.

One thing that has not changed is that all unit string specifications
understood by the original UDUNITS package are also understood by the
new UDUNITS-2 package.

Please visit the webpage or email <support-udunits@unidata.ucar.edu> if
you have questions or comments.

Regards,
Steve Emmerson
UDUNITS-2 Developer