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20050516: UDUNITS - How to express scaled units



Mark,

> Date: Mon, 16 May 2005 15:01:36 -0600 (MDT)
> Organization: NOAA
> Keywords: 200505162101.j4GL1a0Z007433
> To: support-udunits:@laraine.unidata.ucar.edu
> Subject: UDUNITS - How to express scaled units?
> From: "Mark Ohrenschall" <address@hidden>

The above message contained the following:

> Institution: NOAA
> Package Version: irrelevant
> Operating System: irrelevant
> Hardware Information: irrelevant
> Inquiry: I'm using UDUNITS as a convention for a controlled vocabulary -- not
> as a software package.
> 
> I'm wondering how to describe data that is not in degrees celsius, but in
> tenths of degrees celsius -- it's integer data with an implied decimal point.

The name of the physical quantity whose unit is "degrees celsius" is
"celsius temperature" -- so I would think that the name of your physical
quantity would be something like "decicelsius temperature".
Alternatively, you could continue to name it "degrees celsius" with the
understanding that any non-unity scaling factor would have to be taken
into account in order to obtain that quantity.

The UDUNITS package supports the following unit specifications for such
a physical quantity:

    degC/10
    degree_Celsius/10
    deg_C/10

    0.1 degC
    0.1 degree_Celsius
    0.1 deg_C

> Incidentally, I notice that "kg" is permissible but "km" is not.

The UDUNITS package supports "km" as a composite of a "k" prefix and an
"m" base-unit:

    $ udunits
    You have: km
    You want: 
        Definition: "1000 meter"
    You have: km
    You want: m
        <m> = <km>*1000
        <m> = <km>/0.001
    You have: ^D

> So
> furthermore, if I have data that is in units of kilometers, apparently I have
> to express that data in thousands of meters. How do I express the 10^3 scaling
> factor in this case? (And the 10^-1 scaling factor in the prior case?)
> 
> Thank you

Regards,
Steve Emmerson

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