Hi Steve,
Fresh from sorting the fallout from units of 'mg N/l' in Europe I'm with you all the way. To me a photon isn't a unit. A mole (which used to be called an Einstein for photons), or a dimensionless count then OK.
Cheers, Roy.
________________________________________
From: Steve Emmerson [emmerson at ucar.edu]
Sent: 27 November 2014 17:58
To: Charlie Zender
Cc: CF Metadata Mail List
Subject: Re: [CF-metadata] New UDUnits units for information: "byte" and "octet"
Charlie & CF-Metadaters,
On Wed, Nov 26, 2014 at 8:27 PM, Charlie Zender <zender at uci.edu<mailto:zender at uci.edu>> wrote:
Now UDUnits has "molecule" and "byte". They (Steve)
are receptive to well-justified proposals, so do not feel daunted
in transmitting to them the suggestion for "photon".
Please don't request such "units". I beg you.
Think about it. How many things exist like "molecule" or "photon". Here's the start of a list:
tents
clouds
giraffes
desks
people
...
etc., etc., etc. The number of such "units" is, effectively, infinite.
Adding such units is the wrong way to go about solving the problem of adding quantity-semantics to data values. It would be much better to have the names of the variables be things like
"number_of_tents"
"number_of_clouds"
"number_of_giraffes"
"number_of_desks"
"number_of_people"
"number_of_molecules"
"number_of_bytes"
"number_of_bits"
and whose units were "1" than to try to incorporate such semantic information into a unit. The power of units is that there's a limited number of them: many physical quantities can have the same unit. The US National Institute of Standard and Technology agrees (see sections 7.4 and 7.5 of <
http://physics.nist.gov/Pubs/SP811/sec07.html>).
A *physical quantity* library should be used for situations in which it's desirable to have a program automatically convert between, for example, "bits" and "bytes". Such a library would do for physical quantities what the UDUNITS library does for units. It would, for example, know how to convert values between "bits" and "bytes". It could also know how to perform co-ordinate system transformations, such as converting practical salinity values to density. The algorithms for such a library have already been worked-out in multiple packages (VisAD springs to mind, IBM and the Laboratory for Atmospheric and Space Physics have also created such libraries).
Please don't request that the UDUNTS package be polluted in order to do a job that's best done elsewhere.
With regards,
Steve Emmerson
(I feel better now. Thanks! :-)
This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. Any material supplied to NERC may be stored in an electronic records management system.
Received on Thu Nov 27 2014 - 12:23:22 GMT
