Module cesium 

Cesium heightmap-1.0 terrain tile format.

The legacy Cesium terrain format. Each tile is a regular grid of 16-bit heights (default 65 × 65, north → south, west → east) plus a 1-byte child-availability mask. Optional extensions follow: a water mask (1 byte uniform or 256 × 256 bytes), then oct-encoded per-vertex normals (2 bytes per vertex).

Specification: https://github.com/CesiumGS/cesium/wiki/heightmap-1.0

Layout

+------------------------------------+
| u16 LE heights (size×size × 2 B)   |
+------------------------------------+
| u8 child mask                      |
+------------------------------------+
| water mask (optional, 1 or 256² B) |
+------------------------------------+
| oct normals (optional, 2 × N B)    |
+------------------------------------+

Encoded files are typically gzip-compressed; this module returns raw uncompressed bytes — compress them yourself with flate2 or similar.

Height encoding

value = (elevation + 1000) * 5, i.e. range −1000 m … +12107 m at 0.2 m resolution. Use elevation_to_u16 / u16_to_elevation for single-sample conversion.

Structs

ChildTileMask

Child-availability mask: one bit per quadrant indicating whether a child tile exists at the next zoom level.

Constants

MAX_ELEVATION

Maximum elevation representable in metres.

MIN_ELEVATION

Minimum elevation representable in metres.

SCALE

Scale factor: value = (elevation - MIN_ELEVATION) * SCALE.

TILE_SIZE

Default heightmap-1.0 tile side length (Cesium streams 65 × 65 tiles).

Functions

decode_heights

Decode little-endian u16 bytes back to a flat elevation grid.

elevation_to_u16

Encode a single elevation sample (metres) into the heightmap-1.0 u16.

encode_heights

Encode a row-major elevation grid into a freshly allocated Vec<u8>.

encode_heights_into

Encode a row-major width × height elevation grid into a caller-owned little-endian u16 byte buffer. out.len() must equal width * height * 2.

encode_heights_to

Stream-encode a width × height elevation grid as little-endian u16 bytes to a writer. Uses a 4 KiB stack buffer.

iter_heights

Lazily iterate decoded elevations from little-endian u16 bytes. Trailing odd bytes are ignored.

u16_to_elevation

Decode a heightmap-1.0 u16 back to elevation (metres).