support GeoJSON/KML for multiple areas (issue mysociety#136)

mapit/models.py

@@ -12,6 +12,7 @@
 from mapit.managers import Manager, GeoManager
 from mapit import countries
 from mapit.djangopatch import GetQuerySetMetaclass
+from mapit.outputformatter import OutputFormatter
 from django.utils import six
 
 
@@ -343,25 +344,11 @@ def export(self,
             if kml_type == "polygon":
                 out = all_areas.kml
             elif kml_type == "full":
-                out = '''<?xml version="1.0" encoding="UTF-8"?>
-<kml xmlns="http://www.opengis.net/kml/2.2">
-    <Document>
-        <Style id="ourPolygonStyle">
-            <LineStyle>
-                <color>%s</color>
-                <width>2</width>
-            </LineStyle>
-            <PolyStyle>
-                <color>%s</color>
-            </PolyStyle>
-        </Style>
-        <Placemark>
-            <styleUrl>#ourPolygonStyle</styleUrl>
-            <name>%s</name>
-            %s
-        </Placemark>
-    </Document>
-</kml>''' % (line_colour, fill_colour, escape(self.name), all_areas.kml)
+                formatter = OutputFormatter()
+                out = ''
+                out += formatter.kml_header % (line_colour, fill_colour)
+                out += formatter.kml_placemark % (escape(self.name), all_areas.kml)
+                out += formatter.kml_footer
             else:
                 raise Exception("Unknown kml_type: '%s'" % (kml_type,))
             content_type = 'application/vnd.google-earth.kml+xml'

mapit/outputformatter.py

@@ -0,0 +1,52 @@
+# OutputFormatter
+# class for merging kml/geojson output
+
+from django.utils.html import escape
+
+
+class OutputFormatter:
+
+    def __init__(self):
+        self.kml_header =\
+"""<?xml version="1.0" encoding="UTF-8"?>
+<kml xmlns="http://www.opengis.net/kml/2.2">
+    <Document>
+        <Style id="ourPolygonStyle">
+            <LineStyle>
+                <color>%s</color>
+                <width>2</width>
+            </LineStyle>
+            <PolyStyle>
+                <color>%s</color>
+            </PolyStyle>
+        </Style>"""
+        self.kml_placemark =\
+"""
+        <Placemark>
+            <styleUrl>#ourPolygonStyle</styleUrl>
+            <name>%s</name>
+            %s
+        </Placemark>"""
+        self.kml_footer =\
+"""
+    </Document>
+</kml>"""
+
+
+    # [(kml, name)] -> kml
+    def merge_kml(self, kml_arr, line_colour="70ff0000", fill_colour="3dff5500"):
+        output = self.kml_header % (line_colour, fill_colour)
+        for kml in kml_arr:
+            output += self.kml_placemark % (escape(kml[1]), kml[0])
+        output += self.kml_footer
+        return output
+
+    # [(geojson, name)] -> geojson
+    def merge_geojson(self, geojson_arr):
+        output = '{ "type": "FeatureCollection", "features": ['
+        for geojson in geojson_arr:
+            output += '{ "properties": { "name": "%s" }, "type": "Feature", "geometry": %s },'\
+                % (escape(geojson[1]), geojson[0])
+        output = output[:-1]
+        output += "] }"
+        return output

mapit/urls.py

@@ -45,6 +45,8 @@
     url(r'^nearest/(?P<srid>[0-9]+)/(?P<x>[0-9.-]+),(?P<y>[0-9.-]+)%s$' % format_end, postcodes.nearest),
 
     url(r'^areas/(?P<area_ids>[0-9]+(?:,[0-9]+)*)%s$' % format_end, areas.areas),
+    url(r'^areas/(?P<area_ids>[0-9]+(?:,[0-9]+)*)\.(?P<format>kml|geojson)$', areas.areas_polygon),
+    url(r'^areas/(?P<srid>[0-9]+)/(?P<area_ids>[0-9]+(?:,[0-9]+)*)\.(?P<format>kml|geojson)$', areas.areas_polygon),
     url(r'^areas/(?P<area_ids>[0-9]+(?:,[0-9]+)*)/geometry$', areas.areas_geometry),
     url(r'^areas/(?P<type>[A-Z0-9,]*[A-Z0-9]+)%s$' % format_end, areas.areas_by_type),
     url(r'^areas/(?P<name>.+?)%s$' % format_end, areas.areas_by_name),

mapit/views/areas.py

@@ -22,6 +22,7 @@
 from mapit.ratelimitcache import ratelimit
 from mapit import countries
 from mapit.iterables import iterdict
+from mapit.outputformatter import OutputFormatter
 
 
 def add_codes(areas):
@@ -253,6 +254,50 @@ def areas_by_name(request, name, format='json'):
     return output_areas(request, _('Areas starting with %s') % name, format, areas)
 
 
+@ratelimit(minutes=3, requests=100)
+def areas_polygon(request, area_ids, srid='', format='kml'):
+
+    if not srid:
+        srid = 4326 if format in ('kml', 'json', 'geojson') else settings.MAPIT_AREA_SRID
+    srid = int(srid)
+
+    try:
+        simplify_tolerance = float(request.GET.get('simplify_tolerance', 0))
+    except ValueError:
+        raise ViewException(format, _('Badly specified tolerance'), 400)
+
+    area_ids = area_ids.split(',')
+    polygons = []
+    for area_id in area_ids:
+
+        if not re.match('\d+$', area_id):
+            raise ViewException(format, _('Bad area ID specified'), 400)
+        area = get_object_or_404(Area, id=area_id)
+
+        try:
+            polygon, content_type = area.export(srid, format, simplify_tolerance=simplify_tolerance, kml_type='polygon')
+            polygons.append((polygon, area.name))
+
+            if polygon is None:
+                return output_json({'error': _('One or more polygons not found')}, code=404)
+        except TransformError as e:
+            return output_json({'error': e.args[0]}, code=400)
+
+    response = HttpResponse(content_type='%s; charset=utf-8' % content_type)
+    response['Access-Control-Allow-Origin'] = '*'
+    response['Cache-Control'] = 'max-age=2419200'  # 4 weeks
+
+    formatter = OutputFormatter()
+    output = ''
+    if format == 'kml':
+        output = formatter.merge_kml(polygons)
+    if format == 'geojson':
+        output = formatter.merge_geojson(polygons)
+
+    response.write(output)
+    return response
+
+
 @ratelimit(minutes=3, requests=100)
 def area_geometry(request, area_id):
     area = _area_geometry(area_id)