[Qgis-user] Oblique projection and abberrations

[Remi Vannier]

Dear users,

I am new to qGIS and I have struggled with it for 2 days now. I want to
make a map of the world that shows all continents at once, Antarctica
included, with as little distortion as possible on the continents and for
that purpose, I noticed 2 opposite points on the earth (namely 30S 15W in
the south Atlantic Ocean and 30N 165E, around 20 degrees off the coasts of
Japan and Kamchatka) that could play the roles of north and south poles on
my map so that most of the distortion happen in the oceans.

I tried many custom CRS, such as :
- The oblique Mercator :

+proj=omerc +lat_1=60 +lon_1=-15 +lat_2=0 +lon_2=75

(first attempt : I define an equator with 2 points - this one produces the
map that I attached to this e-mail)

- and the general Oblique Transformation :
https://proj.org/operations/projections/ob_tran.html

+proj=ob_tran +o_proj=wink1 +o_alpha=60 +o_lat_c=30 +o_lon_c=15 (not sure
about the right parameters here. I tweaked them so many times I don't
remember exactly which gave the best results).

I'm not exactly sure about what "the point the projection will be rotated
about." means once you touch at the lon_0 value - also, I used Winkel, but
any projection that reduce distortions at the poles would fit my purposes.

As long as I only want to display the "raster" (not sure about that name)
that I took from http://www.naturalearthdata.com/downloads/,
the result is fantastic.

However, when I add the countries borders, I get lines crossing the map,
joining 2 parts of south America that should be close in reality but are on
opposite sides of my map. I suppose the solution should be to rotate the
projection (with the lon0 parameter), but I can't figure out how to do it.
Any help would be appreciated.

In case it matters, I'm using qGIS 3.10.4-A Coruña, on Ubuntu 20.04.

Please receive my apologies if this mailing list isn't the proper place for
such questions.

Edit : I could not attach the image, so I'll simply describe it :
basically, the map has Argentina split in two parts, the south part being
on one edge, the north part being on the other side. The problem is that
these 2 parts are joined with 2 ugly lines that cross the map...

Remi Vannier
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