From d64f07ad9c6882b01b59a707c62c61721f4b9769 Mon Sep 17 00:00:00 2001
From: Codex <codex@geointel.local>
Date: Wed, 15 Jul 2026 19:01:11 +0200
Subject: [PATCH] Normalize DHMV tile mosaic resolution

---
 .../app/services/dhmv_acquisition_service.py  | 35 +++++++++++++------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/backend/app/services/dhmv_acquisition_service.py b/backend/app/services/dhmv_acquisition_service.py
index 818c282c..e410e019 100644
--- a/backend/app/services/dhmv_acquisition_service.py
+++ b/backend/app/services/dhmv_acquisition_service.py
@@ -349,7 +349,7 @@ class DhmvAcquisitionService:
         )
 
     @staticmethod
-    def _mosaic_geotiffs(coverages: list[bytes]) -> bytes:
+    def _mosaic_geotiffs(coverages: list[bytes], expected_resolution_m: float | None = None) -> bytes:
         if len(coverages) == 1:
             return coverages[0]
         try:
@@ -367,20 +367,35 @@ class DhmvAcquisitionService:
         sources = []
         try:
             sources = [memory.open() for memory in memories]
-            crs_values = {str(source.crs) for source in sources}
-            band_counts = {source.count for source in sources}
-            resolutions = {
-                (round(abs(float(source.res[0])), 6), round(abs(float(source.res[1])), 6))
-                for source in sources
-            }
-            if crs_values != {DhmvAcquisitionService.SOURCE_CRS} or band_counts != {1} or len(resolutions) != 1:
+            target_resolution = float(expected_resolution_m or abs(float(sources[0].res[0])))
+            invalid_crs = [index for index, source in enumerate(sources) if source.crs is None or source.crs.to_epsg() != 31370]
+            invalid_bands = [index for index, source in enumerate(sources) if source.count != 1]
+            invalid_resolution = [
+                {
+                    "tile_index": index,
+                    "resolution": [abs(float(source.res[0])), abs(float(source.res[1]))],
+                }
+                for index, source in enumerate(sources)
+                if not all(
+                    math.isclose(abs(float(value)), target_resolution, rel_tol=0.02, abs_tol=0.05)
+                    for value in source.res
+                )
+            ]
+            if invalid_crs or invalid_bands or invalid_resolution:
                 raise AppError(
                     code="DHMV_TILE_MISMATCH",
-                    message="DHMV coverage tiles do not share one CRS, band layout and resolution",
+                    message="DHMV coverage tiles do not match the governed CRS, band layout and resolution",
+                    details={
+                        "invalid_crs_tile_indexes": invalid_crs,
+                        "invalid_band_tile_indexes": invalid_bands,
+                        "invalid_resolution_tiles": invalid_resolution,
+                        "expected_resolution_m": target_resolution,
+                    },
                     status_code=502,
                 )
             mosaic, transform = merge(
                 sources,
+                res=(target_resolution, target_resolution),
                 nodata=DhmvAcquisitionService.NODATA,
                 dtype="float32",
             )
@@ -456,7 +471,7 @@ class DhmvAcquisitionService:
             coverage_hash.update(coverage_content)
             content_types.append(content_type)
             coverages.append(coverage_content)
-        return DhmvAcquisitionService._mosaic_geotiffs(coverages), {
+        return DhmvAcquisitionService._mosaic_geotiffs(coverages, prepared["resolution_m"]), {
             "tile_count": len(request_urls),
             "request_urls": request_urls,
             "response_content_types": content_types,