quiverm creates wrong vectors?
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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 Comments
Walter Roberson
on 26 Jun 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.
Answers (1)
Chad Greene
on 22 May 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 Comment
Chad Greene
on 28 Jul 2014
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