Re: [Matplotlib-users] Basemap plotting data on projection

[ChaoYue <cha...@gm...>]

Dear Scott,

I am sorry for giving no reply. Thanks for your answer. I tried it and it
works fine.

best ,

Chao

On Tue, Apr 30, 2013 at 1:21 PM, Scott Sinclair-4 [via matplotlib] <
ml-...@n5...> wrote:

> Forgot to send to the list <sigh>
>
>
> ---------- Forwarded message ----------
> From: Scott Sinclair <[hidden email]<http://user/SendEmail.jtp?type=node&node=40977&i=0>>
>
> Date: 30 April 2013 13:20
> Subject: Re: [Matplotlib-users] Basemap plotting data on projection
> To: ChaoYue <[hidden email]<http://user/SendEmail.jtp?type=node&node=40977&i=1>>
>
>
>
> On 29 April 2013 23:32, ChaoYue <[hidden email]<http://user/SendEmail.jtp?type=node&node=40977&i=2>>
> wrote:
> > pdata = np.genfromtxt('pdata.txt')
> > pdata = np.ma.masked_greater(pdata,1E20)
> > lonm,latm=m.makegrid(pdata.shape[1],pdata.shape[0])
>
> The problem is here ^^^
>
> The data don't lie on an equally spaced grid in the Mercator
> projection, so it doesn't make sense to ask for the lat/lon
> coordinates of a grid that is equally spaced in this projection. You
> need to determine the *actual* lat/lon coordinates before projecting
> them onto the Mercator map and plotting...
>
> Something like this should work (If you can assume that the data are
> on an equally spaced grid in Equidistant Cyl projection having the
> boundaries specified):
>
> from mpl_toolkits.basemap import Basemap
> import matplotlib.pyplot as plt
>
> # Set up the Equidistant Cyl projection to determine data locations.
> pdata = np.genfromtxt('pdata.txt')
> pdata = np.ma.masked_greater(pdata, 1E20)
> ny, nx = pdata.shape
>
> cyl_basemap = Basemap(projection='cyl', llcrnrlat=9, urcrnrlat=54.5,
>                       llcrnrlon=74, urcrnrlon=142, lat_ts=20,
> resolution='l')
> lon, lat = cyl_basemap.makegrid(nx, ny)
>
> # Set up the Mercator projection for plotting.
> m = Basemap(projection='merc', llcrnrlat=9, urcrnrlat=54.5,\
>             llcrnrlon=74, urcrnrlon=142, lat_ts=20, resolution='l')
> m.drawcountries()
> m.drawcoastlines()
> m.drawmapboundary(fill_color='white')
> m.drawrivers()
>
> x, y = m(lon, np.flipud(lat))
> cs = m.contourf(x, y, pdata)
> m.colorbar(cs)
> plt.show()
>
> Cheers,
> Scott
>
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Chao YUE
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