[R-sig-Geo] Azimuthal equidistant projection and rgdal

[Ashton Shortridge]

Dear Johan (and list),

I'm not a professional cartographer, but I do find myself flipping through 
Snyder's book of map projections every once in a while.

Looking at your results, I don't see anything 'wrong' with the code or the 
results. Yes, the map looks awful, but that is what it should look like. 
Imagine a glass globe of the Earth with outlines of the land masses etched on 
it. Now imagine you have oriented that globe so that you are looking down at 
45N, 90W (somewhere not far from my neck of the woods). What you see as 
"Australia right next to Canada" is from looking 'through the globe', which is 
why Australia appears to be inverted, and why South America seems to fold 
under itself (also Africa).

Now this projection is not really a glass globe, but I hope the metaphor makes 
it a bit clearer. It should also make clearer why people don't normally use 
azimuthal projections for global mapping. Coincidentally it works sorta kinda 
ok from the north pole, but don't plan on it working well from other places.

Hope this is helpful.

Ashton


-----
Ashton Shortridge
Associate Professor			ashton at msu.edu
Dept of Geography			http://www.msu.edu/~ashton
235 Geography Building		ph (517) 432-3561
Michigan State University		fx (517) 432-1671

On 11/12/12, Johan Mazel, wrote:
> Here is the code that I am using and the result.
> The problem on the result is that, on the fourth and last page, it
> looks like some parts of the map are not located where they are
> supposed to be (Australia is thus right next to Canada).
> 
> My only modification is that I removed the xlim and ylim parameters in
> the line "dta <- map("world", xlim=c(-120, -60), ylim=c(0,90),
> plot=FALSE)" in the original script. It obviously has a impact on the
> final output but I can`t figure out what is happening.
> 
> Thanks for your time.
> Regards.
> Johan
> 
> 2012/10/25 Johan Mazel <johan.mazel at gmail.com>:
> > Hi
> > I am trying to use the solution rpesented here:
> > https://stat.ethz.ch/pipermail/r-sig-geo/2007-December/002939.html.
> > 
> > However it looks like the shifted (from the north pole) map is
> > displayed on top on the original azimuthal equidistant projection
> > centered on the north pole.
> > Is there any way to correct this ?
> > 
> > Thanks for your time.
> > Regards.
> > Johan