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

[Johan Mazel]

Thanks for your answer.

Regarding your last paragraph, I am not really sure to understand.
Do you mean that the result is expected in regards to the script (and
rgdal use) ?
Or do you mean that azimuthal equidistant projection is not
possible/valid on any other points than the two poles ? Because, if it
is the latter, Synder's book seems to disagree. If you look at figure
41.C, it looks like azimuthal equidistant projection centered on a
different point than on of the two pole is possible.

Thanks a lot for your time.
Johan

2012/11/12 Ashton Shortridge <ashton at msu.edu>:
> 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
>