| Overlaying gridded winds on satellite data [message #44816] |
Tue, 19 July 2005 21:17  |
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Chris[3]
Messages: 7
Registered: July 2005
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Junior Member |
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Hello all...this maybe a rather simple question...but for some reason I
am having problems and getting rather frustrated. I am hoping that you
guys may have an answer for me. I have visible satellite data which is
in NetCDF format which I can easily get displayed. However, my problem
is laying gridded wind barbs...which are in 900x900 arrays to print on
top of the satellite data. Everytime I do it...the latitudes and
longitudes do not match up correctly...they are close but not correct.
Does anyone know how I could fix this? Thanks for all the help.
Sincerely,
A Frustrated Graduate Student
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| Re: Overlaying gridded winds on satellite data [message #44898 is a reply to message #44816] |
Fri, 22 July 2005 09:56  |
K. Bowman
Messages: 330
Registered: May 2000
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Senior Member |
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In article <20050722.083335.706043324.21076@buckley.atm.ox.ac.uk>,
"Christopher Lee" <cl@127.0.0.1> wrote:
This won't add anything of substance to this topic. ;-)
I think the terms westerly, northerly, etc. are pre-scientific usages that have
persisted into scientific applications. From a physicist's point a view, air
moving from north to south would have a velocity vector pointing southward. The
average person, however, is more interested in where the wind is coming from
than where is is going to (a northerly wind, being from the north, is cold, etc.)
To confuse things further, the oceanographic usage is the reverse of the
meteorological usage. That is, an easterly current is toward the east. This
does make sense, as a ship is more interested in where a current will carry it,
than where the water came from.
The dictionary has both senses of the word (toward and east as well as from the
east). To avoid confusion, I tend to use westward, rather than easterly.
Ken Bowman
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| Re: Overlaying gridded winds on satellite data [message #44908 is a reply to message #44816] |
Fri, 22 July 2005 00:33 |
Chris Lee
Messages: 101
Registered: August 2003
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Senior Member |
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In article <MPG.1d496725a4655cc989a24@news.frii.com>, "David Fanning"
<davidf@dfanning.com> wrote:
> Christopher Lee writes:
>
>> I've never used the stationplot/windbarb programs. Can the STATIONPLOT
>> function show the cloud coverage (in the circle)? Or is the 3/4 filled
>> circle the symbol for a weatherstation?
> It could be made to show the cloud coverage, I'm sure, but currently is
> is the 3/4 filled circle symbol for a weather station.
> Cheers,
> David
>
Yeah, ...., you might want to reverse all the words I used, (not just the
westerly/westward etc. ALL of them :) the post might make sense
then..going now :(
Chris.
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| Re: Overlaying gridded winds on satellite data [message #44909 is a reply to message #44816] |
Fri, 22 July 2005 00:31 |
Chris Lee
Messages: 101
Registered: August 2003
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Senior Member |
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In article <DFODe.15$ce4.7452@news.uswest.net>, "R.G. Stockwell"
<no@email.please> wrote:
> "Christopher Lee" <cl@127.0.0.1> wrote in message
> news:20050721.082817.1875335928.19310@buckley.atm.ox.ac.uk.. .
>> Wind barbs point in the direction the wind is coming FROM. Hence the
>> terms westward (winds coming from the west) and eastward (winds coming
>> from the east) etc.
> You forgot to include the minus sign out front. :) Eastward blows
> towards the east. Eastward = Westerly (out of the West). Colin Hines,
> the great Canadian Physicist, had a great line about the confusion
> between this terminology. I don't remember what it was, so I'll make
> one up.
>
Yeah, uh, oops. I meant eastertly and westerly...obviously :) I'm sure
the first `draft' was worded differently.
Chris.
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| Re: Overlaying gridded winds on satellite data [message #44919 is a reply to message #44816] |
Thu, 21 July 2005 08:03 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Christopher Lee writes:
> Wind barbs point in the direction the wind is coming FROM. Hence the
> terms westward (winds coming from the west) and eastward (winds coming
> from the east) etc.
>
> http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/wnd.rxml
> http://www.rap.ucar.edu/weather/info/about_windbarb.html
> http://sanangelo.tamu.edu/bookmark/wind_dir.htm
> http://www.al.noaa.gov/WWWHD/pubdocs/windbarb.html
> (this one sounds `wrong' at first, but it really is correct, the feathers
> are on the back of the `arrow', also tells you which way the feathers
> point)
>
> Of course, if the users wind vectors are wrong, there's no convincing
> them otherwise. Wind vectors are usually northerly(to the north) and
> easterly(to the east), but I've seen westerly data (you could
> obviously use keywords like /WESTERLY and /EASTERLY).
In light of this information I have reverted to my original
notion of how to draw the wind arrow. I have also improved
the documentation so that it is clear what direction I assume
the positive wind vectors are pointing in. In the northern
hemisphere, the "feathers" on the arrow shaft are drawn in
the clockwise direction (which is what I was doing previously),
but I have added a SOUTHERN_HEMISPHERE keyword to draw the
feathers in a counterclockwise direction, which is apparently
the norm for our friends down under.
And while I was hacking around, I also fixed a small problem
with the CLIP keyword.
So, I expect this to be the definitive word on the subject. :-)
You can find the updated program here:
http://www.dfanning.com/programs/windbarb.pro
> I've never used the stationplot/windbarb programs. Can the STATIONPLOT
> function show the cloud coverage (in the circle)? Or is the 3/4 filled
> circle the symbol for a weatherstation?
It could be made to show the cloud coverage, I'm sure, but
currently is is the 3/4 filled circle symbol for a weather
station.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Overlaying gridded winds on satellite data [message #44921 is a reply to message #44816] |
Thu, 21 July 2005 07:53 |
R.G. Stockwell
Messages: 363
Registered: July 1999
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Senior Member |
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"Christopher Lee" <cl@127.0.0.1> wrote in message
news:20050721.082817.1875335928.19310@buckley.atm.ox.ac.uk.. .
> Wind barbs point in the direction the wind is coming FROM. Hence the
> terms westward (winds coming from the west) and eastward (winds coming
> from the east) etc.
You forgot to include the minus sign out front. :)
Eastward blows towards the east. Eastward = Westerly (out of the West).
Colin Hines, the great Canadian Physicist, had a great line about the
confusion
between this terminology. I don't remember what it was, so I'll make one
up.
"One walks forwards, one does not walk backwardserly".
The point of course was that everyone should use the terms *wards, and
banish
*erly from the literature.
Having said that, I do recognize that "an eastward wind" often means that it
is
an easterly wind. So basically no one can conclude what the frelling
direction
of the wind is, there is a 180 degree ambiguity.
"David Fanning" <davidf@dfanning.com> wrote in message
news:MPG.1d4873bfdf7ab7a5989a20@news.frii.com...
...
> I'm not making any more changes in this program until
> someone sends me a definitive reference for wind barbs.
..
The barbs are *erly, i.e. what direction the wind came from.
Arrows should be *wards, i.e. what direction the wind is blowing.
What better definitive reference than a semi-anonymous usenet posting.
Also, for barbs, see http://www.al.noaa.gov/WWWHD/pubdocs/windbarb.html
Cheers,
bob (the human, not to be confused with JD's pointer pointing to a big pile
of data)
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| Re: Overlaying gridded winds on satellite data [message #44928 is a reply to message #44816] |
Thu, 21 July 2005 00:28 |
Chris Lee
Messages: 101
Registered: August 2003
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Senior Member |
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In article <MPG.1d4873bfdf7ab7a5989a20@news.frii.com>, "David Fanning"
<davidf@dfanning.com> wrote:
> I'm not making any more changes in this program until someone sends me a
> definitive reference for wind barbs. This program has generated more
> unsolicited and contradictory advice than any I have ever written! If I
> now change the direction of the barbs, all hell will break loose. If
> *you* want to do it, however, look in the code for PLOTS commands. :-)
> Cheers,
> David
Wind barbs point in the direction the wind is coming FROM. Hence the
terms westward (winds coming from the west) and eastward (winds coming
from the east) etc.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/wnd.rxml
http://www.rap.ucar.edu/weather/info/about_windbarb.html
http://sanangelo.tamu.edu/bookmark/wind_dir.htm
http://www.al.noaa.gov/WWWHD/pubdocs/windbarb.html
(this one sounds `wrong' at first, but it really is correct, the feathers
are on the back of the `arrow', also tells you which way the feathers
point)
Of course, if the users wind vectors are wrong, there's no convincing
them otherwise. Wind vectors are usually northerly(to the north) and
easterly(to the east), but I've seen westerly data (you could
obviously use keywords like /WESTERLY and /EASTERLY).
I've never used the stationplot/windbarb programs. Can the STATIONPLOT
function show the cloud coverage (in the circle)? Or is the 3/4 filled
circle the symbol for a weatherstation?
Chris L.
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| Re: Overlaying gridded winds on satellite data [message #44940 is a reply to message #44816] |
Wed, 20 July 2005 14:52 |
Chris[3]
Messages: 7
Registered: July 2005
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Junior Member |
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Hey David,
Understandable...I don't blame you at all for not changing it. I will
try working with it and see what I can do. Thanks again for your help.
Chris
David Fanning wrote:
> Chris writes:
>
>> Hey David...I just wanted to thank you again for all of your
>> help...it's been great and I have learned a lot. I have one more quick
>> question for you...and I promise I'll try to not bother you again. With
>> the wind barb procedure...the second direction is the correct
>> way...however the barbs point in the wrong direction...do you know
>> which part of the code I can fix this in?
>
> I'm not making any more changes in this program until
> someone sends me a definitive reference for wind barbs.
> This program has generated more unsolicited and contradictory
> advice than any I have ever written! If I now change the
> direction of the barbs, all hell will break loose.
>
> If *you* want to do it, however, look in the code
> for PLOTS commands. :-)
>
> Cheers,
>
> David
>
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Overlaying gridded winds on satellite data [message #44942 is a reply to message #44816] |
Wed, 20 July 2005 14:44 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Chris writes:
> Hey David...I just wanted to thank you again for all of your
> help...it's been great and I have learned a lot. I have one more quick
> question for you...and I promise I'll try to not bother you again. With
> the wind barb procedure...the second direction is the correct
> way...however the barbs point in the wrong direction...do you know
> which part of the code I can fix this in?
I'm not making any more changes in this program until
someone sends me a definitive reference for wind barbs.
This program has generated more unsolicited and contradictory
advice than any I have ever written! If I now change the
direction of the barbs, all hell will break loose.
If *you* want to do it, however, look in the code
for PLOTS commands. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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