Merge pull request #443 from Open-Earth-Foundation/on-1643

feat: add area to city boundaries and own endpoint

global-api/requirements.txt

@@ -26,4 +26,5 @@ dns-cache==0.3.*
 openpyxl==3.1.*
 pytest==8.1.1
 pytest-cov==4.1.0
-httpx==0.27.0
+httpx==0.27.0
+pyproj==3.6.*

global-api/routes/city_boundaries_endpoint.py

@@ -7,6 +7,10 @@
 from decimal import Decimal
 from shapely.geometry import Point, shape
 from shapely.wkt import loads
+import pyproj
+from functools import partial
+from shapely.ops import transform
+import math
 
 api_router = APIRouter(prefix="/api/v0")
 
@@ -21,6 +25,37 @@ def db_query(locode):
 
     return row
 
+def epsg_code(polygon):
+    """Calculate the UTM zone and corresponding EPSG code for a polygon"""
+    # Calculate centroid of the polygon
+    centroid = polygon.centroid
+    longitude = centroid.x
+    latitude = centroid.y
+
+    # Calculate UTM zone from centroid longitude
+    zone_number = math.floor((longitude + 180) / 6) + 1
+
+    # Determine the hemisphere and corresponding EPSG code
+    if latitude >= 0:
+        code = 32600 + zone_number
+    else:
+        code = 32700 + zone_number
+
+    return code
+
+def get_area(geometry):
+    polygon = loads(geometry)
+    code = epsg_code(polygon)
+
+    proj = partial(
+        pyproj.transform,
+        pyproj.Proj("epsg:4326"), # lat/lon
+        pyproj.Proj(f'epsg:{code}')
+    )
+
+    utm_polygon = transform(proj, polygon)
+    area = utm_polygon.area / 10.0**6 # in km^2
+    return area
 
 @api_router.get("/cityboundary/city/{locode}")
 def get_city_boundary(locode: str):
@@ -29,12 +64,28 @@ def get_city_boundary(locode: str):
     if not city:
         raise HTTPException(status_code=404, detail="City boundary not found")
 
+    area = get_area(city.geometry)
+
     return {
         "city_geometry": city.geometry,
         "bbox_north": city.bbox_north,
         "bbox_south": city.bbox_south,
         "bbox_east": city.bbox_east,
         "bbox_west": city.bbox_west,
+        "area": area
+    }
+
+@api_router.get("/cityboundary/city/{locode}/area")
+def get_city_area(locode: str):
+    city = db_query(locode)
+
+    if not city:
+        raise HTTPException(status_code=404, detail="City boundary not found")
+
+    area = get_area(city.geometry)
+
+    return {
+        "area": area
     }
 
 @api_router.get("/cityboundary/locode/{lat}/{lon}")