Re: [Matplotlib-users] Background basemaps in Basemap

[Jeff W. <js...@fa...>]

On 8/26/12 5:44 AM, klo uo wrote:
> On Sun, Aug 26, 2012 at 12:18 AM, Jeff Whitaker <js...@fa...> wrote:
>> Klo:  The image in interpolated to the Basemap projection region. This is
>> slow - the main reason to use the WMS is to avoid this by having it done on
>> the server side.
> All right, that's the right way anyway
>
>
>> The trick is to figure out what the EPSG projection code is based on the
>> Basemap projection info, and pass that information to the WMS server so it
>> can do the interpolation.
> Yes, and also to pass right `size` parameter as aspect ratio needs to be correct
> Do you want me to try to pair both projections (Basemap name and WKID
> and WKT as they call it)?

Klo:  Since epsg codes comprise a very small subset of possible Basemap 
projections, it may be better to just allow Basemap to accept an epsg 
kwarg.  That keyword would be required in order to use a WMS to display 
a map background. This may be tricky though, since Basemap needs more 
information to define a map projection region than is provided by the 
epsg code.  We may have to start with just a few supported epsg codes 
and then add more as necessary.

I added a testwms.py example to my fork 
(https://github.com/jswhit/basemap.git) that shows how to use three 
different map projections (epsg codes).

-Jeff

-Jeff
>
>
>> Here's an example for south polar stereographic:
>>
>> width = 12000.e3
>> plt.figure()
>> basemap_url =\
>> "http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_Imagery_World_2D/MapServer/export?\
>> bbox=%d,%d,%d,%d&\
>> bboxSR=3412&\
>> imageSR=3412&\
>> size=800,800&\
>> dpi=128&\
>> format=png32&\
>> f=image" % (-width/2,-width/2,width/2,width/2)
>> m =\
>> Basemap(projection='stere',resolution='i',lon_0=0,lat_0=-90,lat_ts=-70,\
>>          width=width,height=width,rsphere=(6378273,6356889.449))
>> m.imshow(plt.imread(urllib2.urlopen(basemap_url)),origin='upper')
>> m.drawmeridians(np.arange(-180,180,30),labels=[0,0,0,1],color='y')
>> m.drawparallels(np.arange(-80,-0,10),labels=[1,0,0,0],color='y')
>> m.drawcoastlines()
>> plt.show()
>>
> Looks beautifully :)
>
> As said later today I'll look at Nokia maps and then will try to look
> for WMS servers.