i.sentinel.download: catch WKT too long with -b flag (#56)

i.sentinel.download: catch WKT too long with -b flag:

Rationale: RFC 2616 HTTP/1.1 imposes a 2000 char limit on WKT when sent via HTTP GET (sentinelsat).

Hence:
* raise fatal error when AOI map (-b flag) has too many vertices, recommending to use 'v.generalize' to simplify the boundaries
* check added if AOI map contains areas (by ninsbl)
* use vector_info_topo() from PyGRASS rather than GRASS Python scripting API

grass7/imagery/i.sentinel/i.sentinel.download/i.sentinel.download.py

@@ -167,14 +167,25 @@ def get_aoi(vector=None):
     if vector:
         args['input'] = vector
 
+    if gs.vector_info_topo(vector)['areas'] <= 0:
+        gs.fatal(_("No areas found in AOI map <{}>...").format(vector))
+    else:
+        gs.warning(_("More than one area found in AOI map <{}>. \
+                      Using only the first area...").format(vector))
+
     # are we in LatLong location?
     s = gs.read_command("g.proj", flags='j')
     kv = gs.parse_key_val(s)
     if '+proj' not in kv:
         gs.fatal('Unable to get AOI: unprojected location not supported')
     geom_dict = gs.parse_command('v.out.ascii', format='wkt', **args)
-    geom = geom = [key for key in geom_dict][0]
+    num_vertices = len(str(geom_dict.keys()).split(','))
+    geom = [key for key in geom_dict][0]
     if kv['+proj'] != 'longlat':
+        gs.message(_("Generating WKT from AOI map ({} vertices)...").format(num_vertices))
+        if num_vertices > 500:
+            gs.fatal(_("AOI map has too many vertices to be sent via HTTP GET (sentinelsat). \
+                        Use 'v.generalize' to simplify the boundaries"))
         coords = geom.replace('POLYGON((', '').replace('))', '').split(', ')
         poly = 'POLYGON(('
         poly_coords = []
@@ -184,6 +195,12 @@ def get_aoi(vector=None):
             for key in coord_latlon:
                 poly_coords.append((' ').join(key.split('|')[0:2]))
         poly += (', ').join(poly_coords) + '))'
+        # Note: poly must be < 2000 chars incl. sentinelsat request (see RFC 2616 HTTP/1.1)
+        if len(poly) > 1850:
+            gs.fatal(_("AOI map has too many vertices to be sent via HTTP GET (sentinelsat). \
+                        Use 'v.generalize' to simplify the boundaries"))
+        else:
+            gs.message(_("Sending WKT from AOI map to ESA..."))
         return poly
     else:
         return geom
@@ -277,7 +294,7 @@ def list(self):
             else:
                 ccp = 'cloudcover_NA'
 
-            print ('{0} {1} {2} {3}'.format(
+            print('{0} {1} {2} {3}'.format(
                 self._products_df_sorted['uuid'][idx],
                 self._products_df_sorted['beginposition'][idx].strftime("%Y-%m-%dT%H:%M:%SZ"),
                 ccp,
@@ -390,7 +407,7 @@ def set_uuid(self, uuid_list):
 
 def main():
     user = password = None
-    api_url='https://scihub.copernicus.eu/dhus'
+    api_url = 'https://scihub.copernicus.eu/dhus'
 
     if options['settings'] == '-':
         # stdin