WRF/Antarctic image renderer not correct

[StasJ]

1. Import WRF/Antarctic
2. Add an image renderer
3. Add a 2D renderer with landmask for reference

For some datasets, such as WRF/antarctic/antarctic_02, nothing is visible when an image renderer is created

The default image renderer will be missing the main land features. If you play with the extents you can get more land to appear.

[clyne]

The bundled maps NaturalEarth and BigBlueMarble have Mercator projections, which are only valid between 85 degrees north and south. We need to include maps that will work with with data at extreme latitudes.