Ortho projection fails at south pole in pcolormesh

まだ誰も着手していません。

I am plotting gridded satellite data using basemap 1.0.7 (I can't get 1.0.8 via pip yet). The grid is 0.25 degrees resolution, global coverage.

For polar views, I use pcolormesh. It works fine for the north polar view:

```
bmap = Basemap(projection='ortho', lat_0=90, lon_0=270, resolution='c')
show_map = bmap.pcolormesh(lons, lats, darray, vmin=vminval, vmax=vmaxval,
norm=norm, cmap=this_cmap, alpha=1.0, latlon=True)
```

but the corresponding map centered on the south pole plots garbage:

```
bmap = Basemap(projection='ortho', lat_0=-90, lon_0=270, resolution='c')
show_map = bmap.pcolormesh(lons, lats, darray, vmin=vminval, vmax=vmaxval,
norm=norm, cmap=this_cmap, alpha=1.0, latlon=True)
```

However, pcolor plots correctly at the south pole. This one is fine:

```
bmap = Basemap(projection='ortho', lat_0=-90, lon_0=270, resolution='c')
show_map = bmap.pcolor(lons, lats, darray, vmin=vminval, vmax=vmaxval,
norm=norm, cmap=this_cmap, alpha=1.0, latlon=True)
```

In this case, my gridded data array is pretty small and the time difference between pcolormesh and pcolor is negligible, but I'm guessing this is something that ought to be fixed, unless it already has been addressed in 1.0.8.

提供されている北極点および南極点の Basemap の例で、pcolormesh と pcolor を使用して問題を再現し、その後 Basemap の pcolormesh 実装と投影の処理を調べます。南極点の正射投影 pcolormesh が、北極点のケースにリグレッションを起こすことなく、pcolor と同じ正しい地図を生成すれば修正は完了です。

索引モデルが issue の本文から書いたものです。