Re: elevation becomes altitude

• To: John J Brecht <john.brecht@xxxxxxx>
• Subject: Re: elevation becomes altitude
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Tue, 17 Sep 2002 09:05:40 -0600

John-

John J Brecht wrote:

After a long hiatus, I'm back to my VisAD project! I'm trying to get some old code working with the latest version of VisAD and I'm having this problem.

I am trying to create some data sets with the following MathType:

(Time, ((Longitude, Latitude) -> (Overlay, Elevation)))

where "overlay" is something like temperature or precipitation. The overlays for some set of such data sets always cover the same geographic region, and thus I use the same elevation file for each one. My source data sets are in the form of text files, which I convert to NetCDF files with a small app I wrote. When I open a data set created in this way in the VisAD spreadsheet, I find that my elevation data have become "altitude." Why is this? How do I prevent it? My code to create the elevation MathType looks like this:

RealType elevation = RealType.getRealType("Elevation", SI.meter);

When a netCDF file is read in, it uses the StandardQuantity
database to create a controlled vocabulary for netCDF variables.
Thus, something named "time" with units compatible with
seconds will be given a RealType of RealType.Time.  Same is
true for a variable "lat" with units compatible with degrees
which will end up with RealType.Latitude for a RealType.
Elevation with units of length (m, ft, km) ends up with
a RealType of RealType.Altitude.  If it was an Elevation
angle with units of degrees, it would not get the RealType.Altitude
labelling.  You could add an alias to RealType.Altitude of
"Elevation" if you want to use Elevation instead of Altitude,
but this is not done automatically.

Steve Emmerson may want to comment more on this, but it's been
this way for a while looking at the CVS logs (1999/01/20?).

Don

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

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