Re: [Matplotlib-users] basemap imshow() extents

[Jeff W. <jef...@no...>]

On 8/20/12 4:41 PM, Scott Henderson wrote:
> I'm having trouble with transform_scalar() and imshow() with basemap. 
> Essential I have data from satellite tracks that are either smaller or 
> larger than the map extent, so I don't want to use Basemap.imshow() 
> which sets the 'extent' keyword automatically.
>
> I tried following the following suggestion, but I can't get things to 
> line up..
> http://comments.gmane.org/gmane.comp.python.matplotlib.general/25085
>
> I suspect I've done something wrong in the code below?:

Scott:  If you use the pcolormesh or contourf Basemap methods (instead 
of imshow), you can specify the map projection coordinates of your data 
and it will be plotted correctly (whether or not it covers the whole map 
projection region).

-Jeff
>
>
> # -------------------------------
> from mpl_toolkits.basemap import Basemap
> import matplotlib.pyplot as plt
>
> LL = (-68, -26)
> UR = (-66, -21)
> bmap = Basemap(projection='merc',
>                llcrnrlat=LL[1],
>                urcrnrlat=UR[1],
>                llcrnrlon=LL[0],
>                urcrnrlon=UR[0],
>                resolution='i',
>                suppress_ticks=False,
>                ax=ax)
> bmap.drawcountries(linewidth=1)
>
> # Overlay image with extents that don't match map boundaries
> nLon, nLat = image.shape
> LL = (-69.915, -31.161)
> UR = (-65.075, -17.334)
> dy = -0.006666664
> lats = UR[1] + dy * np.arange(nLat)
> extent = (LL[0], UR[0], LL[1], UR[1])
> nx = nLon; ny = nLat
> image_xy = bmap.transform_scalar(image, lons, lats[::-1], nx, ny)
> x, y = bmap(extent[:2],extent[2:])
> extent_xy = (x[0], x[1], y[0], y[1])
> im = plt.imshow(image_xy, extent=extent_xy)
>
>
>
> -- 
> ---------------
> Scott T. Henderson
> http://www.geo.cornell.edu/eas/gstudent/sth54/contact.html
>
>
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