Andrew Straw wrote:
> I've been playing around with stereographic projections, and it appears
> that the bounding-box for the 'stere' projection isn't computed. Being
> blissfully unaware of all the complexities involved, I thought I'd send
> this email to see if there's an easy way to deal with the situation.
> Basically, I'm trying to plot on an equatorial stereographic projection
> created like so:
> m=Basemap(projection='stere', lat_ts = 0.0, lat_0 = 0, lon_0 = 90.0)
> This creates a projection that seems to work well, but the problem is
> that the [ll|ur]crn* attributes aren't set to anything useful, meaning
> that lots of the nice basemap goodies aren't working (drawmeridians, etc.)
Andrew: The [ll|ur]crn* have default values which don't work very well
for the stereographic projection (-90,+90,-180,+180). You'll have to
set them yourself when you create the Basemap instance.
> (Note: I don't really understand what the lat_ts is doing -- the
> docstring says it is the "natural origin". I can't find reference to
> this at http://en.wikipedia.org/wiki/Stereographic_projection . I guess
> this is related to the discussion of "scale error at the extremities"
> , and thus I assume that if lat_ts is set to lat_0, the scale factor
> will be 1 at the point of tangency. )
AFAICT, lat_ts is the latitude of 'true scale', whatever that means. I
set the docstring based upon the info at
> So, the question is, can some default bounding box be computed for
> equatorial (and possibly oblique) stereographic projections in any
> reasonable way? It would be nice to make plots like those found on the
> wikipedia page.
You should be able to make all those plots without too much difficulty -
just some trial and error in choosing the corners of the plot region.
If you are making a polar stereographic projection, you can use
projection='npstere' or 'spstere' and set the bounding latitude (the
latitude that is tangent to the plot boundary - see the polarmaps.py
example) and Basemap will determine the corners for you automatically.
I don't know of any obvious way to do this for the equatorial case -
it's pretty hard to guess what the user might want. I welcome any
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328