Terrain Tile Format

Terrain is stored as a directory of square tiles: one Terrain.json manifest plus one .riff file per tile.

Terrain.json

{
  "origin": { "latitude": 35.3826, "longitude": -83.4954 },
  "tileDimension": 500,
  "heightmapResolution": 513,
  "tiles": [
    { "x": 0, "y": 0, "min": 600, "max": 667 }
  ]
}

Field	Meaning
`origin`	Latitude/longitude of world position (0, 0), the south-west corner of tile (0, 0).
`tileDimension`	Tile edge length in meters.
`heightmapResolution`	Height samples per tile edge. Defaults to 513 when absent.
`tiles[].x`, `tiles[].y`	Tile position. `x` increases east (+X), `y` increases north (+Z).
`tiles[].min`, `tiles[].max`	The tile’s height range in meters. Must match the tile’s `RHGI` chunk.

Leave tileDimension (500) and heightmapResolution (513) as the game writes them. Other values are untested, and changing either in an existing tile set does not convert its tiles.

Tile (x, y) covers world X from x * tileDimension to (x + 1) * tileDimension, and world Z over the same range using y. Positions may be negative.

Each tile is stored as tile_XXX_YYY.riff, with the position zero-padded to at least three digits, for example tile_004_012.riff or tile_-001_000.riff.

RIFF container

Tiles are standard RIFF files. All integers are little-endian.

Offset	Size	Value
0	4	`RIFF`
4	4	`int32` size of everything after this field
8	4	Form type `RRT0`
12	…	Chunks

Each chunk is a 4-byte ASCII id, an int32 payload size, then the payload. A payload with an odd size is followed by one pad byte, which the size does not include.

Chunks may appear in any order. Readers should skip chunks they do not recognize.

Texture chunks

RHGT and RBIO hold rasters with this payload layout:

Offset	Size	Value
0	4	Pixel format: `R16` , `R8` , `RFLT`, `RGBA`, `RGB` , or `RBC4` (BC4 block-compressed)
4	4	`int32` width
8	4	`int32` height
12	…	Pixels, rows packed with no padding

Pixel (x, y) is at index y * width + x. Row 0 is the south edge and column 0 is the west edge.

Chunks

`RHGI` — height info

12 bytes:

Offset	Type	Value
0	`int32`	Tile format version: `0` = no biome raster, `1` = has `RBIO`
4	`int32`	Minimum height, meters
8	`int32`	Maximum height, meters

`RHGT` — heights

R16, heightmapResolution x heightmapResolution (513 x 513). Each sample is an unsigned 16-bit value scaled linearly between the RHGI min and max:

height = sample / 65535 * (max - min) + min
sample = round((height - min) / (max - min) * 65535)

Samples sit on the tile’s grid vertices. The first and last rows and columns lie exactly on the tile edges, so neighboring tiles share their edge samples, and those samples should be equal.

The game also reads RFLT heights (32-bit float meters, min/max ignored), but always writes R16.

`RBIO` — biome raster

R8, 256 x 256. Each texel is a biome class code covering 1/256 of the tile, sampled at the texel center. The values are categories, so the chunk must stay R8. Block compression or interpolation produces codes that don’t exist.

The codes currently in use are listed below. Fetched land cover data is mapped to the family codes (multiples of 10). Dirt and Gravel are written by biome painting in the Map Editor. Ballast is applied at runtime by map features and is not normally stored in tiles.

Code	Biome	Status
0	Unknown (no data)	No vegetation
10	Water	Supported
20	Bare	Placeholder sparse grass only
21	Ballast	Ballast texture, no vegetation
22	Dirt	Dirt texture, no vegetation
23	Gravel	Gravel texture, no vegetation
30	Grass	Supported
40	Shrub	Supported
50	Trees	Supported
60	Wetland	Placeholder vegetation
70	Crops	Placeholder vegetation
80	Built	No vegetation
90	Ice	Not supported; for permanent ice/glaciers

Codes are grouped in families of 10, with variations in the units digit. Codes 128 and above are reserved for asset packs.