3857

app.py

@@ -301,22 +301,19 @@ async def generate_i3s(request: GenerateI3SRequest):
         if not coords or len(coords) < 9: # At least 3 points (3 * 3)
              raise HTTPException(status_code=400, detail="Invalid coordinates. Need at least 3 points (lon, lat, alt).")
 
-        # 1. Determine UTM Zone for projection
-        # We need meters for correct CGA generation and I3S placement
-        lon0 = coords[0]
-        lat0 = coords[1]
+        # 1. Project to Web Mercator (EPSG:3857)
+        # Why? 
+        # - It uses Meters (good for CGA generation/scaling).
+        # - It is standard for Web Maps/I3S supported by Cesium.
+        # - Avoids complexity of dynamic UTM zones.
         
-        zone = int((lon0 + 180) / 6) + 1
-        is_north = lat0 >= 0
-        utm_epsg = (32600 if is_north else 32700) + zone
+        target_epsg = 3857 
+        logger.info(f"Projecting I3S geometry to EPSG:{target_epsg} (Web Mercator)")
         
-        logger.info(f"Projecting I3S geometry to EPSG:{utm_epsg} (Zone {zone})")
+        transformer = pyproj.Transformer.from_crs("EPSG:4326", f"EPSG:{target_epsg}", always_xy=True)
         
-        transformer = pyprt.GeometryTransformer = pyproj.Transformer.from_crs("EPSG:4326", f"EPSG:{utm_epsg}", always_xy=True)
-        
-        # 2. Project Points to UTM
-        # coords is [lon, lat, alt, lon, lat, alt...]
-        utm_coords = []
+        # 2. Project Points
+        utm_coords = [] # Variable name kept for minimal diff, but now it's Web Mercator
         num_points = len(coords) // 3
         
         for i in range(num_points):
@@ -326,15 +323,14 @@ async def generate_i3s(request: GenerateI3SRequest):
             cz = coords[idx+2]
             
             ux, uy = transformer.transform(cx, cy)
-            # Z stays same (Alt in meters)
             utm_coords.extend([ux, uy, cz])
             
-        # 3. Calculate Anchor (UTM) to keep numbers small for float32 precision in CGA
+        # 3. Calculate Anchor (Mercator)
         anchor_x = utm_coords[0]
         anchor_y = utm_coords[1]
         anchor_z = utm_coords[2]
         
-        # 4. Localize (UTM - Anchor)
+        # 4. Localize
         local_coords = []
         for i in range(num_points):
             idx = i * 3
@@ -355,16 +351,13 @@ async def generate_i3s(request: GenerateI3SRequest):
         os.makedirs(output_dir, exist_ok=True)
         
         enc_options = {
-            'sceneType': 'Global', # Can also be 'Local', but 'Global' works with appropriate Wkid
-            'sceneWkid': '4326', # Output in UTM
+            'sceneType': 'Global', 
+            'sceneWkid': str(target_epsg), # 3857
             'baseName': 'SceneLayer',
             'sceneName': 'SceneLayer',
             'writePackage': False, 
             'compression': False, 
             'outputPath': output_dir,
-            
-            # Critical: Tell Encoder the offset we subtracted
-            # For I3S/PyPRT, globalOffset matches the sceneWkid coordinate system
             'globalOffset': [anchor_x, anchor_y, anchor_z] 
         }