Global Digital Elevation Model (DEM) tiles from the Copernicus GLO-30 dataset, pre-processed into 256x256 chunks in OZCHNK01 merged format for efficient web serving.

Source

Copernicus DEM GLO-30 (30-meter resolution) from the European Space Agency. Original COG tiles downloaded from AWS Open Data: https://copernicus-dem-30m.s3.eu-central-1.amazonaws.com/

License

Copernicus Licence (free for most uses). See: https://copernicus.eu/user-license

Format

Binary merged format (OZCHNK01):

Magic: 8 bytes "OZCHNK01"
Version: 2 (Copernicus = Float32)
Grid: Variable ROWS x COLS (depends on tile dimensions)
Index: Array of [4-byte offset, 4-byte size] per chunk
Data: Concatenated zlib-compressed 256x256 Float32 chunks

Tile Grid

Internal COG tiles: 1024x1024 pixels
Each split into 4x4 = 16 chunks of 256x256
Edge tiles may have fewer chunks
Data type: Float32 (4 bytes/pixel)

File Naming

Files are organized by latitude band:

Path: {lat_dir}/{basename}.merged
Example: N00/COPDEM_N00_00_E006_00_DEM.merged

Coverage

Global land areas at 30m resolution (~90GB total, ~26,450 tiles).

Usage

For use with OpenZenith elevation API. Each merged file contains all 256x256 chunks for one Copernicus tile, allowing efficient range requests to fetch individual chunks.

To read a chunk:

Open the merged file
Read the 12-byte header (magic + version + rows + cols)
Read the index: rows*cols entries of [offset, size]
Seek to the chunk offset, read size bytes
Decompress with zlib to get 256x256 Float32 pixel data
Elevation value = float32 at row*256 + col

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