Resolve "Add height from OSM `height` and `min_height` tags"

Closes #16 (closed)

\approve @ds @pdlmora

building/02_process/height_and_floorspace/height_and_floorspace.py

@@ -40,16 +40,14 @@ class HeightAndFloorspaceRule:
         # If they are present, the floorspace of a building can be calculated. OpenStreetMap
         # buildings can also contain a `height` tag but this tag is only parsed without the
         # floorspace being estimated.
-        try:
-            stories, floorspace = self.get_stories_and_floorspace_from_osm(tags, area)
-        # OSM can have unexpected data types and unexpected content in their tagging scheme,
-        # therefore we do not raise an exception in case of a ValueError, but instead ignore
-        # the values.
-        except ValueError:
-            stories, floorspace = None, None
+        stories, floorspace = self.get_stories_and_floorspace_from_osm(tags, area)
         if stories:
             gem_taxonomy_height.append(stories)
 
+        height = self.get_height_from_osm(tags)
+        if height:
+            gem_taxonomy_height.append(height)
+
         # If any of the number-of-stories and height tags are found in OpenStreetMap, they are
         # returned.
         if len(gem_taxonomy_height) > 0:
@@ -130,6 +128,36 @@ class HeightAndFloorspaceRule:
 
         return "+".join(story_tags), floorspace
 
+    def get_height_from_osm(self, tags: dict):
+        """
+        Get the height of a building, based on the `height` and `min_height` tags. The
+        information about parsing the tags comes from
+        https://wiki.openstreetmap.org/wiki/Key:building:levels.
+
+        Args:
+            tags (dict):
+                Building tags, such as the building levels or building type.
+
+        Returns:
+            A string formatted according to the `height` tag in the GEM Taxonomy.
+        """
+
+        # Parse the height tag from OpenStreetMap.
+        height = self.tag_to_float(tags, "height")
+        if not height:
+            return None
+
+        # Check if there is a `min_height` tag.
+        min_height = self.tag_to_float(tags, "min_height")
+        if min_height:
+            height -= min_height
+
+        # Check if the height is higher than 0.
+        if height <= 0:
+            return None
+
+        return f"HHT:{height:.2f}"
+
     def tag_to_float(self, tags: dict, tag_key: str):
         """
         Try to parse a tag as a floating point value. If the value cannot be parsed, return
@@ -152,8 +180,9 @@ class HeightAndFloorspaceRule:
         if tag_value is None or tag_value == "":
             return None
 
-        # If the tag does exist, try to convert it to float. If that raises a `ValueError`,
-        # return None.
+        # OSM can have unexpected data types and unexpected content in their tagging scheme,
+        # therefore we do not raise an exception in case of a ValueError, but instead ignore
+        # the values.
         try:
             return float(tag_value)
         except ValueError: