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Re: GRIB data question [message #78330 is a reply to message #78323]

Thu, 10 November 2011 15:08

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Kenneth P. Bowman writes:

> A quick and simple sanity check is to plot a global map of
> surface temperature or air temperature at the lowest level
> (typically 1000 hPa). The continents stand out quite clearly.

Sigh...

OK, I'm an old man (well, a hell of a lot older than I was
when I started worrying about map projections about three
weeks ago for a new book I am writing!), and I've been around
the block a couple of times, so problems with data don't
particularly surprise me. But, in the example Mark presents,
the only "clue" to how to apply the map projection information
in the file to the extremely limited-spatial-extent data that
is in the file (nothing like something where continents are
going to stand out!) is the word "Alaska" in his description
of the data set. One would presume that you might find an outline
of Alaska somewhere near the image data!

I have every confidence that Mark has displayed the data
correctly. My only concern is how he knew to display it in
that particular way. Relying on the word "Alaska" seems
particularly fraught with unpleasant possibilities. :-(

This is an issue that I would like to address in the book,
because I used to run into it over and over again when I
was working at NSIDC. How do you know whether or not
your data is upside down!? It seems a simple thing, but
it really is not. And it is MOST embarrassing to have this
pointed out to you in the middle of an important presentation
reporting your results!

The problem, as you suggest, is easier to manage with global
data sets. It is a LOT harder when the spatial extent of the
data is limited. When you are in the middle of the ocean, as
we appear to be with this data set, the bets as to which way
is up get iffy, at best.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: GRIB data question By: David Fanning on Fri, 11 November 2011 06:45
		Re: GRIB data question By: Kenneth P. Bowman on Fri, 11 November 2011 06:04
		Re: GRIB data question By: Kenneth P. Bowman on Fri, 11 November 2011 05:55
		Re: GRIB data question By: David Fanning on Thu, 10 November 2011 15:08
		Re: GRIB data question By: Kenneth P. Bowman on Thu, 10 November 2011 14:40
		Re: GRIB data question By: David Fanning on Thu, 10 November 2011 11:25
		Re: GRIB data question By: David Fanning on Thu, 10 November 2011 11:16
		Re: GRIB data question By: Kenneth P. Bowman on Thu, 10 November 2011 10:56
		Re: GRIB data question By: David Fanning on Thu, 10 November 2011 09:22
		Re: GRIB data question By: Fabzou on Thu, 10 November 2011 08:54

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