Support precision for GeometryCollection geometries in fiona.transform

fiona/_transform.pyx

@@ -162,8 +162,8 @@ def _transform_geom(
         g = geom
 
     if precision >= 0:
-
-        if g['type'] == 'Point':
+    
+        def round_point(g):
             coords = list(g['coordinates'])
             x, y = coords[:2]
             x = round(x, precision)
@@ -172,8 +172,10 @@ def _transform_geom(
             if len(coords) == 3:
                 z = coords[2]
                 new_coords.append(round(z, precision))
-
-        elif g['type'] in ['LineString', 'MultiPoint']:
+            return new_coords
+
+
+        def round_linestring(g):
             coords = list(zip(*g['coordinates']))
             xp, yp = coords[:2]
             xp = [round(v, precision) for v in xp]
@@ -184,8 +186,10 @@ def _transform_geom(
                 new_coords = list(zip(xp, yp, zp))
             else:
                 new_coords = list(zip(xp, yp))
+            return new_coords
+
 
-        elif g['type'] in ['Polygon', 'MultiLineString']:
+        def round_polygon(g):
             new_coords = []
             for piece in g['coordinates']:
                 coords = list(zip(*piece))
@@ -198,8 +202,9 @@ def _transform_geom(
                     new_coords.append(list(zip(xp, yp, zp)))
                 else:
                     new_coords.append(list(zip(xp, yp)))
+            return new_coords
 
-        elif g['type'] == 'MultiPolygon':
+        def round_multipolygon(g):
             parts = g['coordinates']
             new_coords = []
             for part in parts:
@@ -216,7 +221,24 @@ def _transform_geom(
                     else:
                         inner_coords.append(list(zip(xp, yp)))
                 new_coords.append(inner_coords)
-
-        g['coordinates'] = new_coords
+            return new_coords
+
+        def round_geometry(g):        
+            if g['type'] == 'Point':
+                g['coordinates'] = round_point(g)
+            elif g['type'] in ['LineString', 'MultiPoint']:
+                g['coordinates'] = round_linestring(g)
+            elif g['type'] in ['Polygon', 'MultiLineString']:
+                g['coordinates'] = round_polygon(g)
+            elif g['type'] == 'MultiPolygon':
+                g['coordinates'] = round_multipolygon(g)
+            else:
+                raise RuntimeError("Unsupported geometry type: {}".format(g['type']))
+
+        if g['type'] == 'GeometryCollection':
+            for _g in g['geometries']:
+                round_geometry(_g)
+        else:
+            round_geometry(g)
 
     return g

tests/test_transform.py

@@ -70,3 +70,15 @@ def test_axis_ordering(crs):
     geom = {"type": "Point", "coordinates": [-8427998.647958742, 4587905.27136252]}
     g2 = transform.transform_geom("epsg:3857", crs, geom, precision=3)
     assert g2["coordinates"] == pytest.approx(rev_expected)
+
+
+def test_transform_issue971():
+    """ See https://github.com/Toblerity/Fiona/issues/971 """
+    source_crs = "epsg:25832"
+    dest_src = "epsg:4326"
+    geom = {'type': 'GeometryCollection', 'geometries': [{'type': 'LineString',
+                                                          'coordinates': [(512381.8870945257, 5866313.311218272),
+                                                                          (512371.23869999964, 5866322.282500001),
+                                                                          (512364.6014999999, 5866328.260199999)]}]}
+    geom_transformed = transform.transform_geom(source_crs, dest_src, geom, precision=3)
+    assert geom_transformed['geometries'][0]['coordinates'][0] == pytest.approx((9.184, 52.946))