fix: use Math.round for tile latStart/lonStart to handle GeoTIFF FP precision (#820)

Copernicus DEM GeoTIFF files for latitude bands N03, N15, and N63 have
ModelTiepoint Y coordinates slightly below the expected integer
(e.g., 63.99999999999999 instead of 64.0). Math.floor(minLat) then
rounded down to the wrong tile index, causing entire latitude bands
of terrain data to be unfindable.

Fixes #817

Co-authored-by: wilhel1812 <wilhelm@linksim.link>

Author: wilhel1812

src/lib/copernicusTerrainClient.ts

@@ -307,8 +307,8 @@ const parseCopernicusTileInMain = async (
   }
   return {
     key: tileKey,
-    latStart: Math.floor(minLat),
-    lonStart: Math.floor(minLon),
+    latStart: Math.round(minLat),
+    lonStart: Math.round(minLon),
     size: Math.max(width, height),
     width,
     height,

src/workers/copernicusTileParser.worker.ts

@@ -59,8 +59,8 @@ const parse = async (message: TileParserRequestMessage): Promise<TileParserRespo
         key: message.key,
         dataset: message.dataset,
         path: message.path,
-        latStart: Math.floor(minLat),
-        lonStart: Math.floor(minLon),
+        latStart: Math.round(minLat),
+        lonStart: Math.round(minLon),
         width,
         height,
         elevations: out,