# Ala-Kul terrain provenance ## DEM - Copernicus DEM GLO-30 Public, AWS 2021 release, accessed 2026-10-26. - Tile: `Copernicus_DSM_COG_10_N42_00_E078_00_DEM`. - Original: https://copernicus-dem-30m.s3.amazonaws.com/Copernicus_DSM_COG_10_N42_00_E078_00_DEM/Copernicus_DSM_COG_10_N42_00_E078_00_DEM.tif - Dataset / license entry: https://registry.opendata.aws/copernicus-dem/ - License and attribution guidance: https://dataspace.copernicus.eu/explore-data/data-collections/copernicus-contributing-missions/collections-description/COP-DEM - Crop WGS84: west 78.48, south 42.28, east 78.59, north 42.36. - Reprojection: EPSG:32644 (UTM 44N), bilinear resampling, 257 × 257 sample centres. Heights remain in metres; no vertical exaggeration. This is a surface model, not a surveyed hiking map. The grid is a browser-resolution derivative, not native 30 m resolution. Heights retain the source vertical datum (EGM2008); no conversion to ellipsoidal height. - Original SHA-256 is embedded in `terrain.json`. Generated with `scripts/import-ala-kul.py`. - Colours, snow threshold, atmospheric haze and illumination are artistic; no satellite imagery is used. produced using Copernicus WorldDEM-30 © DLR e.V. 2010-2014 and © Airbus Defence and Space GmbH 2014-2018 provided under COPERNICUS by the European Union and ESA; all rights reserved ## Shoreline © OpenStreetMap contributors, ODbL 1.0: https://www.openstreetmap.org/copyright Source way 27426053, accessed 2026-10-26: https://www.openstreetmap.org/api/0.6/way/27426053/full.json The reprojected shoreline polygon is in the `lake` field of `terrain.json`, distributed under ODbL. Lake plane level is estimated from the DEM at the shoreline; it is not a verified water gauge reading. Water material is illustrative, with a subtle roughness animation; physical reflection/wave simulation is not implemented. Location reference: https://www.geonames.org/7626600/ala-kul-lake.html Photograph attribution: /images/CREDITS.md ## Satellite surface — updated 2026-10-26 The 3D surface now uses the actual EOxCloudless Sentinel-2 **2016** mosaic, CC BY 4.0. The live WMTS capabilities identify the `s2cloudless` layer as the 2016 release: https://tiles.maps.eox.at/wmts/1.0.0/WMTSCapabilities.xml Official usage guidance: https://cloudless.eox.at/documentation/faq License: https://creativecommons.org/licenses/by/4.0/ EOxCloudless https://cloudless.eox.at by EOX IT Services GmbH (Contains modified Copernicus Sentinel data 2016) Fetched one WMS GetMap JPEG using service https://tiles.maps.eox.at/ with VERSION=1.1.1, LAYERS=s2cloudless, SRS=EPSG:4326, BBOX=78.46,42.26,78.61,42.38, WIDTH=2048, HEIGHT=2048, FORMAT=image/jpeg. This older acquisition is not live imagery. It can contain mosaic seams and baked-in shadows. Newer EOX vintages require different usage rights and are not used here. Adaptation: reprojected to EPSG:32644 at the exact terrain vertex footprint using bilinear resampling, compressed to WebP quality 92. UV north/south orientation matches the DEM row order. No AI imagery, stock mountain texture or copied Everest asset is used. Input checksum and attribution are in imagery.json. The texture is embedded in this experience; no standalone satellite tile service is provided. The DEM derivative was regenerated at 385 × 385 samples (about 24 m grid spacing; this does not increase the ~30 m source accuracy). Its source-derived vertical range is 2443.5–4346.7 m. The terrain keeps real proportions. The previous flat water overlay and artificial snow/rock vertex colours are removed; lake, snow and rock appearance now come from the registered satellite image itself. ## Single-acquisition surface — 2026-10-27 Default surface is now Copernicus Sentinel-2 L2A, acquired 2025-09-28, item `S2C_43TGG_20250928_0_L2A` via Earth Search's public Sentinel COG archive. This historical acquisition shows substantial snow cover. The 2016 EOX surface remains an explicitly selectable alternative; its license and credits above still apply. Contains modified Copernicus Sentinel data 2025. Terms: https://dataspace.copernicus.eu/terms-and-conditions Collection: https://earth-search.aws.element84.com/v1/collections/sentinel-2-l2a Item asset URL, acquisition timestamp and pixel checksum: imagery-2025.json. The actual 10 m true-colour COG was read by a range/window request, reprojected to the exact existing DEM footprint, resampled and compressed to WebP quality 94. No generated pixels or fictitious height detail were added. The importer rejects uncovered full-black RGB pixels; individual zero-valued colour channels are valid. Script: scripts/prepare-sentinel-texture.py. Seasonal snow and baked-in sun shadows belong to that acquisition. Geometry remains the same Copernicus ~30 m DEM; photogrammetric cliff detail is not claimed. ## Visual water and close-range material treatment The source DEM remains unchanged on disk. Rendered vertices inside the mapped lake polygon are lowered only as needed to one metre below a representative lake plane, whose level is derived from the median interior DEM samples. This is a hydro-flattening display correction, not inferred bathymetry or a new survey. The plane uses the exact source shoreline polygon. Ripples, planar reflections, atmospheric sprite clouds and procedural sub-metre bump shading are artistic rendering layers. They do not increase the geographic resolution of the ~30 m DEM. No third-party cloud, rock, water or audio assets were copied. Audio is synthesized. The land alpha mask is rasterized directly from the saved OSM shoreline at 2048 × 2048 (scripts/prepare-lake-mask.py) and clips land triangles beneath the water to avoid grid-shaped shoreline artifacts. It has the same ODbL provenance as the outline; it is not an independently surveyed shoreline. Close-range bump shading fades out between 90 and 500 metres to avoid distant noise/aliasing.