Sort-of parsing OSM files

osm-slurp.py

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+from sys import stdin
+from math import hypot, ceil
+from xml.parsers.expat import ParserCreate
+
+from networkx import Graph
+from shapely.geometry import MultiLineString, MultiPolygon, Polygon
+from pyproj import Proj
+
+merc = Proj('+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over')
+
+def segmentize(ring, distance):
+    """
+    """
+    coords = [ring.coords[0]]
+
+    for curr_coord in list(ring.coords)[1:]:
+        prev_coord = coords[-1]
+
+        dx, dy = curr_coord[0] - prev_coord[0], curr_coord[1] - prev_coord[1]
+        steps = ceil(hypot(dx, dy) / distance)
+        count = int(steps)
+
+        while count:
+            prev_coord = prev_coord[0] + dx/steps, prev_coord[1] + dy/steps
+            coords.append(prev_coord)
+            count -= 1
+
+    return coords
+
+class ParserOSM:
+
+    nodes = None
+    ways = None
+    way = None
+
+    def __init__(self):
+        self.p = ParserCreate()
+        self.p.StartElementHandler = self.start_element
+        self.p.EndElementHandler = self.end_element
+        #self.p.CharacterDataHandler = char_data
+
+    def parse(self, input):
+        self.nodes = dict()
+        self.ways = dict()
+        self.p.Parse(input)
+
+        parsed = dict()
+
+        for (id, way) in self.ways.items():
+            if not way['key'][0]:
+                # no-name, no way!
+                continue
+
+            key = tuple(way['key'])
+
+            if key not in parsed:
+                parsed[key] = []
+
+            parsed[key].append(way['nodes'])
+
+        line = MultiLineString(parsed[(u'Harrison Street', u'secondary')])
+        poly = line.buffer(20, 3)
+
+        if hasattr(poly, 'geoms'):
+            geoms = []
+
+            for geom in poly.geoms:
+                exterior = segmentize(poly.exterior, 10)
+                interiors = [segmentize(interior, 10) for interior in poly.interiors]
+                geoms.append((exterior, interiors))
+
+            poly = MultiPolygon(geoms)
+
+        else:
+            exterior = segmentize(poly.exterior, 10)
+            interiors = [segmentize(interior, 10) for interior in poly.interiors]
+            poly = Polygon(exterior, interiors)
+
+        print poly
+
+        return
+
+        print parsed.keys()
+        print line.buffer(20, 3)
+
+    def start_element(self, name, attrs):
+        if name == 'node':
+            self.add_node(attrs['id'], float(attrs['lat']), float(attrs['lon']))
+
+        elif name == 'way':
+            self.add_way(attrs['id'])
+
+        elif name == 'tag' and self.way:
+            self.tag_way(attrs['k'], attrs['v'])
+
+        elif name == 'nd' and attrs['ref'] in self.nodes and self.way:
+            self.extend_way(attrs['ref'])
+
+    def end_element(self, name):
+        if name == 'way':
+            self.end_way()
+
+    def add_node(self, id, lat, lon):
+        x, y = merc(lon, lat)
+        self.nodes[id] = x, y
+
+    def add_way(self, id):
+        self.way = id
+        self.ways[id] = dict(nodes=[], key=[None, None])
+
+    def tag_way(self, key, value):
+        way = self.ways[self.way]
+
+        if key == 'name':
+            way['key'][0] = value
+        elif key == 'highway':
+            way['key'][1] = value
+
+    def extend_way(self, id):
+        way, node = self.ways[self.way], self.nodes[id]
+        way['nodes'].append(node)
+
+    def end_way(self):
+        self.way = None
+
+p = ParserOSM()
+p.parse(stdin.read())