specify that CF uses UDUNITS-2

[jonathan]

Unidata has released a new version of the udunits package, which fixes some problems in the original version. Although the units supported are very largely the same, CF should specify which version is the reference standard, since there are a few differences. Unidata deprecates the original version. Therefore version 2 should be the CF reference. This ticket proposes to clarify and update the CF standard by

• Replacing all references to UDUNITS with UDUNITS-2.

• Replacing all references to udunits.dat with references to the appropriate xml file of UDUNITS-2.

I'm submitting this as a defect, because I don't think it materially affects the CF standard.

Jonathan Gregory

[jonathan]

I'm closing this ticket because some substantial issues were raised on the email list, so this change can't be made as a defect. For the record, I think we have to note that CF depends on udunits as a standard for formatting the units string, but not as a software package, and we need a CF xml file including some units that aren't standard in udunits. This file should perhaps include the prefix u to stand for 1e-6 i.e. micro, as it does in udunits version 1, as pointed out by Andrew Clegg on the email list.

Jonathan