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quiverm creates wrong vectors?

13 vues (au cours des 30 derniers jours)
Sandra
Sandra le 22 Juin 2012
Commenté : Chad Greene le 28 Juil 2014
Hello,
I am trying to plot wind vectors with quiverm. For some reason, and I would really like to know why, the vectors I get point in the wrong direction, distorted in the x and y direction, compared to when I just plot them with quiver.
This is what I have and use:
ywindlat meshgrid (17x69) (latitude increasing by rows)
xwindlon meshgrid (17x69) (longitude increasing by columns)
u wind (17x69)
v wind (17x69)
then I use the following commands:
load coast
axesm('mercator', 'MapLatLimit' ,[-20 20], 'MapLonLimit' ,[120 -70],...
'ParallelLabel', 'on', 'MeridianLabel', 'on', 'MLabelParallel', 'south', 'Grid', 'on', ...
'PLabelLocation', 10, 'MLabelLocation', 20, 'MLineLocation', 20,'PLineLocation', 10)
plotm(lat,long, 'Color',grey,'linewidth',1)
quiverm(ywindlat,xwindlon, wind_u, wind_v,'black',0.2 )
that gives me different vectors than if I just plotted:
quiver(flipud(wind_u), flipud(wind_v))
What am I missing?
Any help is appreciated a lot
Sandra
  5 commentaires
Sandra
Sandra le 25 Juin 2012
Hi Walter,
I think I have a slight idea why it is distorting them. And it's somewhat embarrassing :-) My U and V input vectors are wind speeds in m/s and not in in lat/long degree units as requested by the quiverm function. Obviously this is not going to work out...(ahhh). Do you know of a way that I can use the quiverm but with actual wind values?
Have a great day
Sandra
Walter Roberson
Walter Roberson le 26 Juin 2012
I have not worked with the Mapping toolkit. Looking around the documentation, I'm thinking that perhaps you need to convert your velocity vectors using reckon() as discussed near the bottom of http://www.mathworks.com/help/toolbox/map/bragdwh.html . Divide your meters/s by 1000 to get the values in kilometers. But to get the arclen parameter for the distance I'm thinking you probably have to find the magnitude of your wind-speed vector... I guess that would be sqrt(u.^2 + v.^2). And I guess the az would be atan2(u,v). Might be easier to do a cart2pol() to calculate the magnitudes and angles.

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Réponses (1)

Chad Greene
Chad Greene le 22 Mai 2014
I recently ran into the same problem. The ncquiverref function scales the vectors correctly, and correctly identifies u as a zonal component of wind and v as the meridional component.
  1 commentaire
Chad Greene
Chad Greene le 28 Juil 2014
The quivermc function is another option. It is an adaption of ncquiverref.

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