Fix angle calculation at 180 degrees

queries.yaml

@@ -1139,13 +1139,22 @@ post_process:
     params:
       source_layer: roads
       start_zoom: 8
-      end_zoom: 16
+      end_zoom: 15
       # setting the following will try to merge linestrings across junctions
       # (i.e: more than 2 roads meeting at a point) where the angle between
       # roads at that point is less than 5 degrees.
       merge_junctions: true
       merge_junction_angle: 5.0
 
+  # we do want to merge at 15, but we don't want to merge junctions becase that
+  # might merge across oneway information, which doesn't get dropped until
+  # zoom < 15.
+  - fn: vectordatasource.transform.merge_line_features
+    params:
+      source_layer: roads
+      start_zoom: 15
+      end_zoom: 16
+
   # simplify roads again, to take advantage of any opportunities opened up
   # by merging roads with the same properties in the previous step.
   - fn: vectordatasource.transform.simplify_layer

test/test_transform.py

@@ -965,3 +965,29 @@ def test_merge_buildings(self):
 
         self.assertEquals(len(result), 1)
         self.assertTrue(result[0].is_valid)
+
+
+class AngleAtTest(unittest.TestCase):
+
+    def _check(self, coords, angle):
+        from shapely.geometry import LineString
+        from vectordatasource.transform import _angle_at
+
+        ls = LineString(coords)
+        self.assertEqual(_angle_at(ls, ls.coords[0]), angle)
+        self.assertEqual(_angle_at(ls, ls.coords[-1]), angle)
+
+    def test_angle_at_zero(self):
+        self._check([[0, 0], [1, 0]], 0)
+
+    def test_angle_at_180(self):
+        self._check([[1, 0], [0, 0]], 0)
+
+    def test_angle_at_90(self):
+        self._check([[0, 0], [0, 1]], 90)
+
+    def test_angle_at_270(self):
+        self._check([[0, 1], [0, 0]], 90)
+
+    def test_angle_at_degenerate(self):
+        self._check([[0, 0], [0, 0]], None)

vectordatasource/transform.py

@@ -3580,6 +3580,13 @@ def _angle_at(linestring, pt):
         dy = -dy
 
     a = math.atan2(dy, dx) / math.pi * 180.0
+
+    # wrap around at exactly 180, because we don't care about the direction of
+    # the road, only what angle the line is at, and 180 is horizontal same as
+    # 0.
+    if a == 180.0:
+        a = 0.0
+
     assert 0 <= a < 180
     return a