aliasfox/openzenith-dem

OpenZenith DEM: Global Elevation & Bathymetry Tiles

Global elevation dataset combining Copernicus GLO-30 (land) and GEBCO 2025 (ocean bathymetry) in Terrarium PNG tile format.

Dataset Description

OpenZenith DEM provides global elevation coverage as Terrarium PNG tiles organized in a standard XYZ tile pyramid. The dataset merges:

• Copernicus GLO-30 (30 arc-second, ~30m resolution) for all global landmass
• GEBCO 2025 (15 arc-second, ~450m resolution) for ocean bathymetry and land fill

The merge priority per pixel:

• Ocean (elevation < 0): GEBCO 2025 bathymetry
• Land: Copernicus GLO-30 (highest accuracy), GEBCO fallback for gaps

Terrarium Encoding

Each tile is a 256×256 RGB PNG with elevation encoded as:

height_meters = (R × 256 + G + B / 256) - 32768

This is the standard format used by MapLibre GL JS, CesiumJS, and Deck.gl for terrain visualization.

Zoom Levels

Zoom	Resolution	Tiles	Size	Source
0-3	~110km	85	7.5MB	GEBCO only
4-6	~14km	4,376	378MB	GEBCO only
7-8	~1.7km	81,920	4.7GB	GEBCO + Copernicus land overlay
9	~850m	262,144	~14GB	GEBCO + Copernicus land overlay

Dataset Structure

tiles/
├── 0/
│   └── 0.png
├── 1/
│   ├── 0/
│   │   └── 0.png
│   └── 1/
│       └── 0.png
├── ...
└── 8/
    ├── 0/
    │   ├── 0/
    │   │   └── 0.png
    │   └── ...
    └── ...

Usage

Python (pip install openzenith)

from openzenith import get_elevation, load_tiles

# Download tiles from HuggingFace (zoom 0-8, ~5GB)
tiles_dir = load_tiles(zoom_levels=[0, 1, 2, 3, 4, 5, 6, 7, 8])

# Query elevation at any lat/lon
elev = get_elevation(40.7128, -74.0060)  # New York City
print(f"NYC elevation: {elev:.1f}m")

# Batch queries
from openzenith import get_elevation_batch
elevations = get_elevation_batch([
    (40.7128, -74.0060),   # New York
    (35.6762, 139.6503),   # Tokyo
    (27.9881, 86.9250),    # Mount Everest
])

Decode tiles directly

from openzenith import decode_tile, encode_tile

# Decode a Terrarium PNG tile to numpy array
with open("tiles/8/217/151.png", "rb") as f:
    data = f.read()

elevation = decode_tile(data)
print(f"Shape: {elevation.shape}")
print(f"Range: {elevation.min():.1f} to {elevation.max():.1f}m")

# Encode back to PNG
png_bytes = encode_tile(elevation)

MapLibre GL JS (Web)

// Add terrain source from R2 (or local tiles)
map.addSource("dem", {
  type: "raster-dem",
  tiles: ["https://openzenith.pages.dev/api/dem-tile/{z}/{x}/{y}"],
  tileSize: 256,
  encoding: "terrarium",
  maxzoom: 10,
});

map.setTerrain({ source: "dem", exaggeration: 1.2 });

CesiumJS (Web)

// Custom Terrarium terrain provider (included in openzenith/globe)
viewer.terrainProvider = createTerrariumTerrainProvider(Cesium);

API Endpoint

# Query elevation
curl "https://openzenith.pages.dev/api/elevation?lat=40.7128&lon=-74.0060"

# Get a tile
curl "https://openzenith.pages.dev/api/dem-tile/8/217/151.png" -o tile.png

# Health check
curl "https://openzenith.pages.dev/api/dem-tile?health=1"

Data Sources

Source	Resolution	Coverage	License
Copernicus GLO-30	30 arc-sec (~30m)	Global land	ESA Open
GEBCO 2025	15 arc-sec (~450m)	Global (land+ocean)	CC-BY 4.0

Technical Details

• Tile format: 256×256 RGB PNG, Terrarium encoding
• Tile pyramid: Standard XYZ (Slippy Map) scheme
• Vertical datum: WGS84 ellipsoidal
• Coordinate system: EPSG:4326 (WGS84)
• NoData encoding: R=0, G=0, B=0 (decodes to NaN)
• Accuracy: Copernicus GLO-30: 3-7m RMSE; GEBCO 2025: ~100m (bathymetry)

Limitations

• Zoom 0-8 tiles are complete and verified
• Zoom 9 tiles are being generated (check dataset updates)
• Ocean bathymetry from GEBCO has lower accuracy than land elevation
• Edge tiles may contain extrapolated data from the source datasets

License

MIT License. The underlying data sources retain their own licenses:

• Copernicus GLO-30: ESA Open (free for any purpose)
• GEBCO 2025: CC-BY 4.0 (attribution required)