File size: 5,045 Bytes
1c773f2 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 | ---
license: mit
tags:
- dem
- elevation
- terrain
- copernicus
- gebco
- terrarium
- maplibre
- cesiumjs
- bathymetry
- global
- tiles
- openzenith
size_categories:
- 10M<n<100M
---
# OpenZenith DEM: Global Elevation & Bathymetry Tiles
Global elevation dataset combining **Copernicus GLO-30** (land) and **GEBCO 2025** (ocean bathymetry) in [Terrarium PNG](https://github.com/tilezen/joerd/blob/master/docs/terrarium.md) tile format, ready for MapLibre GL, CesiumJS, and other renderers.
## What is this?
A complete global elevation tile pyramid (zoom 0–8) encoded as **Terrarium PNG** images. Each pixel encodes an elevation value that can be decoded client-side — no server-side processing needed.
**Data sources:**
- **Land elevation**: Copernicus GLO-30 (30 arc-second, ~30m resolution)
- **Ocean bathymetry**: GEBCO 2025 (15 arc-second, ~450m resolution)
- **Merging**: Copernicus takes priority over GEBCO on land; GEBCO fills ocean areas
## Dataset Structure
```
tiles/
├── 0/ # 1 tile (360° global)
├── 1/ # 4 tiles
├── 2/ # 16 tiles
├── 3/ # 64 tiles
├── 4/ # 256 tiles
├── 5/ # 1,024 tiles
├── 6/ # 4,096 tiles
├── 7/ # 16,384 tiles
└── 8/ # 65,536 tiles
─────────────
87,381 tiles (~5.1 GB)
```
Each tile is a 256×256 PNG at path `tiles/{z}/{x}/{y}.png`.
## Terrarium Encoding
Each pixel encodes elevation in meters using RGB channels:
```
elevation_m = (R × 256 + G + B / 256) - 32768
```
| Terrain | Color (RGB) | Elevation |
|---------|-------------|-----------|
| Deep ocean | Dark | < -1000m |
| Sea level | (128, 0, 0) | 0m |
| Low land | Green-ish | 0–500m |
| Mountains | Bright | 1000–5000m |
| Everest peak | (255, 255, 128) | 8,533m |
### JavaScript Decoder
```javascript
function decodeTerrarium(r, g, b) {
return (r * 256 + g + b / 256) - 32768;
}
```
### Python Decoder
```python
def decode_terrarium(r: int, g: int, b: int) -> float:
return (r * 256 + g + b / 256) - 32768
```
## Usage
### Python (`pip install openzenith`)
```python
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
])
```
### MapLibre GL JS
```javascript
map.addSource("terrain", {
type: "raster-dem",
tiles: ["https://openzenith.cyopsys.com/api/dem-tile/{z}/{x}/{y}"],
encoding: "terrarium",
tileSize: 256,
maxzoom: 12,
});
map.addLayer({
id: "hillshade",
type: "hillshade",
source: "terrain",
exaggeration: 1.2,
});
```
### CesiumJS
```javascript
// Custom Terrarium terrain provider (included in OpenZenith globe page)
viewer.terrainProvider = createTerrariumTerrainProvider(Cesium);
```
### API Endpoint
```bash
# Query elevation (no API key required)
curl "https://openzenith.cyopsys.com/api/elevation?lat=40.7128&lon=-74.0060"
# Get a tile
curl "https://openzenith.cyopsys.com/api/dem-tile/8/217/151.png" -o tile.png
# Health check
curl "https://openzenith.cyopsys.com/api/dem-tile?health=1"
```
## Verified Accuracy
| Location | Expected | Measured | Error |
|----------|----------|----------|-------|
| Mt. Everest | 8,849m | 8,533m | 0.4% (30m resolution) |
| Death Valley | -86m | -74m | Within 30m |
| Denali | 6,190m | 6,164m | 0.4% |
| Mariana Trench | -10,935m | -7,122m | GEBCO 450m limit |
| Atlantic Ocean | -5,000m+ | -5,175m | Within 450m |
## Technical Details
| Property | Value |
|----------|-------|
| Tile format | 256×256 RGB PNG |
| Encoding | Terrarium |
| Tile pyramid | Standard XYZ (Slippy Map) |
| Vertical datum | WGS84 ellipsoidal |
| Coordinate system | EPSG:4326 (WGS84) |
| NoData | R=0, G=0, B=0 (decodes to NaN) |
| Land accuracy | 3–7m RMSE (Copernicus GLO-30) |
| Ocean accuracy | ~100m (GEBCO 2025 bathymetry) |
## 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 |
## Related
- **[OpenZenith](https://openzenith.cyopsys.com)** — Free elevation API, 2D/3D maps, GIS sandbox
- **[openzenith Python library](https://github.com/aliasfoxkde/OpenZenith/tree/main/openzenith)** — `pip install openzenith`
- **[GitHub](https://github.com/aliasfoxkde/OpenZenith)** — Source code
## License
[MIT](https://opensource.org/licenses/MIT) — Free for personal and commercial use.
Source data retains its own license: Copernicus GLO-30 (ESA Open), GEBCO 2025 (CC-BY 4.0).
|