On 7/23/11 9:32 AM, Yoshi Rokuko wrote:
> +----------------------------------------- Jeff Whitaker -----------+
>> Here's the basic idea:
>>
>> 1) read the germany.dat file, use it to create a _geoslib Poly instance,
>> i.e.
>>
>> from mpl_toolkits.basemap import _geoslib
>> b = np.asarray([lons,lats]).T # lons and lats are lists.
>> germanypoly = _geoslib.Polygon(b)
>>
>> 2) loop over all the points on the grid and do
>>
>> inside = _geoslib.Point((lonpt,latpt)).within(germanypoly)
>>
>> filling a boolean array with the values.
>>
>> 3) use this boolean array as a mask to create a masked array from your
>> data. Then, when you plot the masked array with contourf only the
>> points inside germany will be contoured.
>>
>> Give this a try and let us know how it goes.
>>
>> -Jeff
>>
> because of islands it doesn't work as expected i guess?
>
> here is what i did:
>
>>>> bmap = Basemap(projection='aeqd', ...)
>>>> x, y = bmap(lons, lats)
>>>> npoints = 300
>>>> xi = np.linspace(np.amin(x), np.amax(x), npoints*.7178)
>>>> yi = np.linspace(np.amin(y), np.amax(y), npoints)
>>>> zi = griddata(x, y, var, xi, yi)
>>>> inside = np.zeros_like(zi)
>>>> lon, lat = np.loadtxt('germany-lon-lat-np.arr')
>>>> bx, by = bmap(lon, lat)
>>>> b = np.asarray([bx, by]).T
>>>> poly = _geoslib.Polygon(b)
>>>> i = 0
>>>> # i know this is slow, but ...
>>>> for y in yi:
>>>> for x in xi:
>>>> inside.flat[i] = _geoslib.Point((x,y)).within(poly)
>>>> i += 1
>>>> mzi = ma.masked_array(zi, mask=inside)
> here is what it looks like:
> http://rokuko.net/test.png
>
> matlab includes NaNs right before and after islands in the lon
> lat lists, is there something similar ?
Yoshi: Islands would be a problem. I was assuming you had one polygon.
Can you get rid of the islands so you just have one closed polygon to
use for a mask?
-Jeff
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