James Boyle wrote:
> when I call quiver in the Basemap toolkit, the scale keyword has the  
> effect of eliminating all vectors, no matter what value I assign  
> (except None).
> I am using matplotlib 0.87.3 -  Basemap 0.9
> In any case the exact effect of the scale parameter is obscure - how  
> does is scale? units/inch, units/gridbox ???
>
> Thanks for any help.
> --Jim
>
>
> the calls I use are below:
> mercMap =  
> Basemap(llcrnrlon=120.,llcrnrlat=-20,urcrnrlon=200.,urcrnrlat=20.,\
>              resolution='c',area_thresh=10000.,projection='merc',\
>              lon_0=160.,lat_ts=0.)
> istride = 3
> mercMap.quiver(x[::istride,::istride],y[::istride,::istride],uERA[:: 
> istride,::istride],vERA[::istride,::istride],scale=None)
>
>
>   
Jim:  Basemap passes the scale keyword directly to matplotlib quiver.   
 From the docstrings in quiver.py:

 * scale = None | float
            data units per arrow unit, e.g. m/s per plot width;
            a smaller scale parameter makes the arrow longer.
            If None, a simple autoscaling algorithm is used, based
            on the average vector length and the number of vectors.

I just tried changing the projection to 'merc' in the quiver_demo.py 
example, and it looked OK with the default (scale=None).

-Jeff


-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
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