[GIS] Projecting Azimuthal Equidistant global map into circle using QGIS

coordinate systemqgis

I'm fairly new to QGIS/GIS.

I have a shapefile of all the countries in the globe I downloaded from Natural Earth. I'm needing to create two hemisphere maps (similar to these guys I found on Wikimedia) in a azimuthal equidistant projection:
enter image description here
However, I need the western hemisphere to have most of Europe and the US and the Eastern projection to include Asia and Australia. Basically, the center of the map would be the middle of the Atlantic.

I narrowed down the problem to it's my proj language in the CRS, but I'm not sure how to pair the project to a circle.

Any insights?

Best Answer

To get am Azimuthal Equidistant map, follow my answer here:

Manipulating Azimuthal Equidistant Projections in QGIS

But that gives you an image of the whole world. You have to crop that picture to a circle around the point of origin in a second step.

But I'm not sure if you do not rather want an orthographic map:

http://en.wikipedia.org/wiki/Orthographic_projection_%28cartography%29

http://commons.wikimedia.org/wiki/Grey-green_orthographic_projections_maps

This is what you get with

+proj=ortho  +R=6371000 +lat_0=0 +lon_0=7

enter image description here

Related Solutions

[GIS] Manipulating Azimuthal Equidistant Projections in QGIS

Using a simple proj string:

+proj=aeqd +lat_0=51 +lon_0=7

I get this picture from Natural Earth world boundaries, and a 10-degree-grid that should span from -150° to 150°E:

aeqd on a WGS84 ellipsoid

It looks like everything outside of lon_0 +/-90° gets truncated, and parts of the southern hemisphere bended as well.

EDIT

According to this ticket: http://trac.osgeo.org/proj/ticket/211 proj has a problem with reprojecting aeqd data on an ellipsoid.

A simple solution: use a sphere (and not the default ellipsoid) by defining a radius:

+proj=aeqd  +R=6371000 +lat_0=51 +lon_0=7

This gives me the following picture:

aeqd on a sphere

Grid lines are densified to show nice curves.

[GIS] Losing polygons after projecting map in QGIS

The simple reason why QGIS can not draw these polygons is because some of the vertices are on the backside of the globe, and QGIS can not draw a closed polygon with the rest. The GDAL ogr2ogr function in the background is programmed to kick off the whole feature when such an error occurs.

So you have two solutions:

Solution 1: Clip your polygons to the hemisphere

You need Numerical Digitize and CAD Tools plugin for that.

Set the project CRS to ortho projection
create a new point layer in the same projection
with the Numerical Digitize plugin, create the following points:

(should also work with Add delimited text layer)

enable snapping on the point layer
with CAD Tools, select the first three points and create an arc from them
do the same for points 3 - 4 - 1 for the southern hemisphere
change project CRS to WGS84
Save the CAD layer as WGS84 and add that to the canvas
Save your boundary layer also as WGS84 and add it to the canvas
convert the CAD lines to a new polygon layer
remove all except the polygon layers
clip the world boundaries to the CAD polygon layer
set project CRS back to ortho

You should get this picture: world vector in ortho projection

Solution 2: Convert your vector data to raster

in Settings, disable on-the-fly-reprojection
Save your boundary layer as WGS84 and add that to the canvas
Use Raster -> Convert -> Rasterize on the WGS84 layer select x=360 and y=170 as dimensions for the raster (or n*360 and n*170)
Use Raster -> Projection -> Reproject to the ortho projection under another name and add it to the canvas. You will get some errors, but the rest of the raster will do. Don't bother that you see a grey rectangle
Rightclick on the raster layer -> Properties, Style tab
choose pseudo colours
in transparency tab, choose 0 for 100% transparency
Remove the first raster
set project CRS to ortho

you should see the follwing picture: enter image description here

The same method works with rasters, as you can see in my avatar picture ;-)