taking the zoom factor into account

ocitysmap/coords.py

@@ -49,3 +49,13 @@ class BoundingBox:
         """Return a new bbox of the same size + dlat/dlong added on the sides"""
         return BoundingBox(self._lat1+dlat, self._long1 - dlong,
                            self._lat2-dlat, self._long2 + dlong)
+
+    def get_pixel_size_for_zoom_factor(self, zoom = 17):
+        """Return the size in pixels (tuple width,height) needed to
+        render the bounding box at the given zoom factor"""
+        delta_lat = abs(self._lat1 - self._lat2)
+        delta_long = abs(self._long1 - self._long2)
+        pix_x = delta_long * (2 ** (zoom + 8)) / 360
+        pix_y = delta_lat * (2 ** (zoom + 8)) / 180
+        return (int(math.ceil(pix_x)),
+                int(math.ceil(pix_y)))

ocitysmap/map_canvas.py

@@ -93,21 +93,27 @@ class MapCanvas:
     """
     OSM in the background of a canvas used to draw grids and text.
     """
-    def __init__(self, mapfile_path, bbox, grwidth = 800, grheight = 600):
+    def __init__(self, mapfile_path, geographic_bbox, graph_bbox = None):
         """
         @param mapfile_path (string) path the the osm.xml map file
-        @param envelope (BoundingBox) bounding box to render, in
+        @param geographic_bbox (BoundingBox) bounding box to render, in
         latlong (4326) coordinates
-        @param grwidth/grwidth (int) graphical width/height of the
-        rendered area for raster output
+        @param graph_bbox (int) graphical width/height of the
+        rendered area for raster output (None = auto)
         """
         self._projname    = GLOBALS.MAIN_PROJECTION
         self._proj        = mapnik.Projection(self._projname)
-        self._envelope    = mapnik.Envelope(bbox.get_top_left()[1],
-                                            bbox.get_top_left()[0],
-                                            bbox.get_bottom_right()[1],
-                                            bbox.get_bottom_right()[0])
-        self._map         = mapnik.Map(grwidth, grheight, self._projname)
+        if graph_bbox is None:
+            graph_bbox = geographic_bbox.get_pixel_size_for_zoom_factor()
+        elif str(graph_bbox).startswith('zoom:'):
+            graph_bbox = geographic_bbox.get_pixel_size_for_zoom_factor(int(graph_bbox[5:]))
+        self._envelope    = mapnik.Envelope(geographic_bbox.get_top_left()[1],
+                                            geographic_bbox.get_top_left()[0],
+                                            geographic_bbox.get_bottom_right()[1],
+                                            geographic_bbox.get_bottom_right()[0])
+        self._map         = mapnik.Map(graph_bbox[0],
+                                       graph_bbox[1],
+                                       self._projname)
         mapnik.load_map(self._map, mapfile_path)
 
         # Keep geographic bounding box, ignoring one dimension of the

ocitysmap/street_index.py

@@ -178,14 +178,14 @@ class OCitySMap:
         return sorted(map(_humanize_street_label, sl),
                           lambda x, y: cmp(x[0].lower(), y[0].lower()))
 
-    def render_into_files(self, osm_map_file, out_filenames):
+    def render_into_files(self, osm_map_file, out_filenames, zoom_factor):
         GRID_COLOR = '#8BB381'
         l.debug('rendering from %s to %s...' % (osm_map_file, out_filenames))
         g = self.griddesc.generate_shape_file('x.shp')
 
         bbox = self.boundingbox.create_expanded(self.griddesc.height_square_angle/2.,
                                                 self.griddesc.width_square_angle/2.)
-        city = map_canvas.MapCanvas(osm_map_file, bbox)
+        city = map_canvas.MapCanvas(osm_map_file, bbox, zoom_factor)
         city.add_shapefile(g.get_filepath(), GRID_COLOR)
         l.debug('adding labels...')
         for idx, label in enumerate(self.griddesc.vertical_labels):

render.py

@@ -23,6 +23,9 @@ def main():
                       nargs=3, metavar='NAME BBOX',
                       help='Specify a zoomed section by its named '
                            'bounding box.')
+    parser.add_option('-f', '--zoom-factor',
+                      metavar='[0-18]', help='Zoom factor for the'
+                      'rendering (default=16)', type='int', default =16)
     parser.add_option('-x', '--osm-xml', dest='osm_xml', metavar='PATH',
                       help='Path to the osm.xml file')
 
@@ -40,6 +43,11 @@ def main():
         parser.error("Invalid path to the osm.xml file (%s)"
                      % options.osm_xml)
 
+    try:
+        options.zoom_factor = int(options.zoom_factor)
+    except ValueError:
+        parser.error("Invalid zoom factor: %s" % options.zoom_factor)
+
     if not options.output:
         options.output = ['citymap.svg']
 
@@ -68,7 +76,8 @@ def main():
     except KeyboardInterrupt:
         sys.stderr.write(' Aborting.\n')
 
-    renderer.render_into_files(options.osm_xml, options.output)
+    renderer.render_into_files(options.osm_xml, options.output,
+                               "zoom:%d" % options.zoom_factor)
     return 0
 
 if __name__ == '__main__':