Re: Questions about VisAD units.

• To: Gianluca <gianlucky@xxxxxxxxx>
• Subject: Re: Questions about VisAD units.
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Mon, 21 May 2001 09:27:18 -0600

Hi Gianluca-

I'm sure Steve Emmerson will reply to your extension questions and
indicate how they can be used with the netCDf adapter, but I have just a
few comments:

1) salinity and viscosity are quantities that have units and are not
units themselves.

2) m/s is supported already as is m^2/s^2.  I've attached a test program
that will parse a string and return a unit or indicate that the unit is
not supported in VisAD (i.e., not in the default units data base).  If
the units are specified correctly in the netCDF file, then they should
be parsed correctly by the data adapter.  (see the next note for
specifying them correctly)

3) The unit specification is case sensitive.  m/s is not the same as
M/S.  Using the test program:

java TestUnit m/s
Unit = m.s-1

java TestUnit M/S
Unit = 1000000.0 kg.m2.s-3.A-2

Don Murray

> Gianluca wrote:
> 
> Hi all,
>           I have some questions about VisAD units.
> I have some oceanographic's model output in netCDF files, and I will
> want to visualize them using SpreadSheet. The problem is that some
> oceanographic units (as salinity, viscosity, ect.) are not present in
> VisAD DefaultUnitsDB.class, and so I have some question to you.
> 
> 1) Could I add new units to the DefaultUnitsDB?
> 
> 2) I see that there are three unit constructors: ps( ), pn( ), px( ).
> I must use this methods to add new unit?
> 
> 3) For example, one of my variable is U (velocity) who has unit "m/s",
> does VisAD know that it has to take "m" and divide for "s", or I must
> create a unit "m/s" with, for example:
>                     px( "m/s", get("m").divide(get("s"))); ??
> 
> 4) extending 3). Other unit is "m^2/s^2". I have to write "m2/s2" or
> "m^2/s^2" when I make the netCDF file?
> 
> 5) I have a variable named "sigma" that is no-dimensional. How could I
> add to DefaultUnitsDB?
>                     px("sigma", "null");  is good??
> 
> Ciao e Grazie,
> Gianluca
> 
> 

-- 
*************************************************************
Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************

import visad.*;
import visad.data.units.*;

public class TestUnit {

    public static void main(String[] args) {
      if (args.length < 1) {
          System.out.println("Must supply unit string");
          System.exit(0);
      }
      try {
          Unit unit = Parser.parse(args[0]);
          System.out.println("Unit = " + unit);
      }
      catch (Exception e) {
          System.out.println("Unknown unit");
      }
    }
}

• References:
  • Questions about VisAD units.
    • From: Gianluca