Vättern extension, 2026-10-11
© OpenStreetMap contributors, ODbL 1.0: https://www.openstreetmap.org/copyright
Lake: https://www.openstreetmap.org/relation/253599 — multipolygon with islands; ele=88.6 metres. Geometry simplified about 4 m in latitude.
City extracts: Jönköping, Motala, Askersund, Karlsborg. Bounds are in scripts/fetch_vattern.py. Main OSM map API fallback was used after Overpass server failures; original XML retained locally in references/vattern/osm. Complete ways may extend slightly beyond extract boundaries. Buildings use OSM footprints and available height tags; missing building heights/roof forms are estimated.
Terrain: AWS Open Data elevation tiles / Skadi HGT, N57E014, N57E015, N58E014, N58E015. https://registry.opendata.aws/terrain-tiles/
Terrain is sampled onto a 129×257 grid over [14.05,57.68,15.22,58.96], about 500–560 m spacing; not a navigation-grade elevation model. Lake level is flattened to the OSM tag. Heights below the lake level are clamped and the outer 0.04-degree edge blends to the existing simplified scene. Shores are clipped to OSM water geometry; shallow slopes/DEM shoreline interpolation remain approximations.
Map coordinates are WGS84; rendering uses existing EPSG:32633 transform. Existing Baltic map coverage and detailed Bråvalla patch are retained.
