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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