Hatch, Sara J wrote:
>
> Matplotlib Folks,
>
> I tried to use the orthographic projection in the basemap toolkit and
> I’m finding that the parallel lines are not behaving correctly, i.e.,
> there are horizontal lines connecting the left and right side of the
> map boundary where a curved latitude line intersects the map boundary.
> I’ve included a sample script below and a figure illustrating the problem.
>
> import pylab
>
> import mpl_toolkits.basemap as basemap
>
> ortho =
> basemap.Basemap(projection='ortho',lon_0=0,lat_0=50,rsphere=1737.4)
>
> ortho.drawparallels(pylab.arange(-90,90,30))
>
> ortho.drawmeridians(pylab.arange(0,360,30))
>
> ortho.drawmapboundary(fill_color='w')
>
> In addition, how do I change the x/y coordinates the center of the
> projection to be (0,0)? With the above code, the center of the
> bounding circle is at (1737.4,1737.4).
>
> Thanks for the help,
>
> Sara
>
Sara: If you take out the rsphere=1734.4 (thereby using the default
value of 6370997), the jumpy lines go away. rsphere=1734.4 means assume
the earth is a perfect sphere with a radius of 1734.4 meters. That's an
awfully small earth - I think the jumpy lines are a result of roundoff
errors in the map projection calculation for very small spheres. Still,
that shouldn't happen, so I will look into it.
Regarding the x/y coordinate of the middle of the plot - Basemap assigns
the lower left corner of the map projection region an x/y value of 0,0
for most map projections.
-Jeff
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