. . . . "2026-04-08" . . "WGS84 Ellipsoid Significantly Affects HEALPix Cell Assignment at Mid and High Latitudes" . "WGS84 ellipsoid indexing assigns pixels to substantially different HEALPix cells than sphere-based indexing, particularly at mid and high latitudes. At mid-latitudes (+48°), 98% of pixels are assigned to a different cell. This demonstrates that sphere-based HEALPix indexing is unsuitable for European Earth observation data (Copernicus/Sentinel, 45-65°N). " . . " ELLIPSOID ANALYSIS (HEALPix depth 9, sphere vs WGS84):\n \n | Region | Center lat | Pixels in different cell | Jaccard similarity | \n |---------------|------------|--------------------------|-------------------| \n | Equatorial | 0° | 26.6% | 0.9951 | \n | Mid-latitude | +48° | 98.4% | 0.9844 | \n | High-latitude | +62° | 90.8% | 0.9868 |\n | Arctic | +78° | 52.6% | 0.9908 | \n \n At mid-latitudes (Mediterranean, +48°), nearly every pixel (98.4%) is assigned to a different HEALPix cell when using sphere vs WGS84 ellipsoid.\n Polygon coverage Jaccard similarity drops to 0.9844, indicating measurable differences in spatial coverage. The effect peaks at mid-latitudes \n where the WGS84 ellipsoid deviates most from a sphere, and decreases towards the equator and poles. " . " - Uses synthetic raster grids, not real Earth observation data\n - Single HEALPix depth (9) tested -- effect may vary at other depths \n - Four latitude bands only; continuous latitude sweep not performed \n - Does not quantify downstream impact on scientific analyses (e.g., land cover classification accuracy) " . . . . . " Anne Fouilloux" . "2026-04-09T20:59:47.543Z"^^ . . . . . . "NP created using Declaring a replication study outcome according to FORRT" . . "RSA" . "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" . "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" . . .