Re: [Matplotlib-users] plot arrows for wind direction (degrees)

[questions a. <que...@gm...>]

thank you! of course!

On Wed, Oct 5, 2011 at 3:08 PM, Eric Firing <ef...@ha...> wrote:

> On 10/04/2011 05:40 PM, questions anon wrote:
> > Excellent, thank you. That works for both quiver and barb.
> > In regards to the shape that has to do with the netcdf file, wind
> > direction variable also has lat and lon. I ended up needing to slice so
> > I could skip a few points otherwise there was too many arrows on the map.
> > Below is the code that worked in case someone else needs help.
>
> Are you sure it worked correctly?  I don't think so.  See below.
>
> > Thanks again
> >
> > from netCDF4 import Dataset
> > import numpy as N
> > import pylab as plt
> > from numpy import ma as MA
> > from mpl_toolkits.basemap import Basemap
> > import os
> >
> > ncfile=Dataset('E:/temp_winddir/IDZ00026_VIC_ADFD_Wind_Dir_SFC.nc',
> > 'r+', 'NETCDF4')
> > WDIR=ncfile.variables['Wind_Dir_SFC'][20,0::5,0::5]
>
> Don't you need to convert from degrees to radians?  sin and cos (used
> below) expect radians, not degrees.  You can use N.deg2rad(WDIR) to
> convert.
>
> > LAT=ncfile.variables['latitude'][0::5]
> > LON=ncfile.variables['longitude'][0::5]
> > TIME=ncfile.variables['time'][20]
> > ncfile.close()
> >
> > map = Basemap(projection='merc',llcrnrlat=-40,urcrnrlat=-33,
> >                llcrnrlon=139.0,urcrnrlon=151.0,lat_ts=0,resolution='i')
> > x,y=map(*N.meshgrid(LON,LAT))
> > u=1*N.sin(WDIR)
> > v=1*N.cos(WDIR)
> > map.quiver(x,y,u, v)
>
> Assuming you do convert to radians the above will work for your mercator
> projection but it will not align the vectors correctly with respect to
> the parallels and meridians for other projections, so you should use
> map.rotate_vector as in the basemap quiver demo.
>
> Eric
>
>
> >
> > #  otherwise use the barb tool - map.barbs(x,y,u, v)
> >
> > plt.title('Wind Direction')
> > plt.show()
>
>
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