[geofence] add comments for equal area projection

sim/geofence/geofence_lib.ipynb

@@ -78,13 +78,13 @@
       "import mpl_toolkits.basemap.pyproj as pyproj # Import the pyproj module\n",
       " \n",
       "wgs84 = pyproj.Proj(proj='merc', ellps='WGS84') # LatLon with WGS84 datum\n",
-      "ease_grid_global = pyproj.Proj(init='EPSG:3410')\n",
+      "ease_grid_global = pyproj.Proj(init='EPSG:3410') # Equal area projection\n",
       "\n",
       "# lon/lat to x/y grid\n",
       "def lonlat_to_ea_grid(outlines):\n",
       "    return [[ease_grid_global(point[0], point[1]) for point in outline] for outline in outlines]\n",
       "        \n",
-      "    \n",
+      "# define limits of EASE grid, at +-180E, and +-86N\n",
       "def ease_limit_x(x):\n",
       "    if x > 17334193.9437:\n",
       "        return 17334193.9437\n",
@@ -107,7 +107,7 @@
      "language": "python",
      "metadata": {},
      "outputs": [],
-     "prompt_number": 13
+     "prompt_number": 18
     },
     {
      "cell_type": "markdown",