title: Cartopy: Convert point from axes coordinates to lat/lon coordinates
body: <p>I am working on a map plot with Cartopy (<code>TransverseMercator</code> projection). I have a point in axes coordinates (<code>p_a = (0.1, 0.9)</code>) and I need its lat/lon coordinates (i.e., those in <code>PlateCarree</code> projection). How can I achieve this?</p>