Your heightmap.
Your next mountain.

STEP 01

Install the tools once

You need Python 3.10 or later, pipx, and the Windows edition of Ski-E-O! or its demo installed through Steam. Linux with Proton is also supported. You can prepare maps on macOS, but this tutorial’s game launch requires Windows or Linux with Proton.

Launch the game once through Steam, then close it. If you already use Custom Map, update the CLI with the command below and run skieomod update to update the installed loader.

py -m pip install --user pipx
py -m pipx ensurepath

Install the latest published tools and set up the game:

pipx install --force --index-url https://skieomap.emillon.fr/downloads/pypi/ skieo-custom-map
skieomod setup
skieomod --version

setup installs UE4SS, the Custom Map loader and the Veymont example, and remembers the game directories. If it cannot find the game, use skieomod setup --game-dir "PATH TO GAME". Choose the Steam installation folder that contains SkiResortSimulator.

Prefer a graphical interface? With CLI 1.15 or later, run skieomod editor to create or open a source project, import your own heightmap, sculpt terrain in 3D and configure vegetation. The icon toolbar also opens graph/Lua triggers, resources and object properties. Its Build, Test and Play buttons use the same pipeline described below. See the native editor guide and screenshots and the visual scripts and scenarios tutorial, or follow the Ticket Office model tutorial.

Checkpoint: skieomod --version prints a version number. This walkthrough was checked with CLI 1.16.0, a prepared release awaiting publication. The public download is currently 1.15.0. Automatic raw dimensions and the relative test elevation range require 1.12 or later.

STEP 02

Know what your heightmap contains

Already have a heightmap? Start with your own file. Choose the answer that matches it below. Your choice also selects the configuration in step 4. The practice download is a separate option.

What you provide, and what the build calculates

• Source: the file you want to build, referenced by build.heightmap.file.
• Spacing: metres between neighbouring samples. Use the exporter’s value. If you know the intended width, spacing is width_in_metres / (samples_x − 1). Both axes use the same spacing.
• Dimensions: automatic for PNG; assumed square from the sample count for raw R16 when possible. Known raw dimensions override that assumption.
• Elevation: optional for a first test. Without elevation settings, the lowest and highest actual samples become 0 and 1,000 m. This is a relative test range; pixels alone do not reveal real altitudes. For accurate terrain, supply the actual altitude range or the exporter’s scale and offset.

The build calculates the map extent, sample encoding, centred origin and menu preview, then updates the generated terrain fields. You do not need to calculate those fields yourself.

Do not rename a PNG to .r16. Renaming a compressed image does not turn it into raw samples.

STEP 03

Create a map project

Create a working folder, for example SkiEO-maps, and open a terminal in that folder. Keep your original heightmap available for step 4. On Windows, File Explorer’s Open in Terminal action opens PowerShell at the right location.

Create a project for your mountain:

skieomod create map --output my-resort --name "My Mountain" --id author.my-mountain --author "Your name"

Replace Your name and the author prefix with your own name or handle. Keep the ID lowercase and unique, such as snowrider.my-mountain. The starter terrain dimensions do not matter for this workflow: the build will replace them with values derived from your source.

SkiEO-maps/
└── my-resort/
    ├── custom-map.json        Map identity and terrain settings
    ├── Terrain/heightmap.r16  Starter slope (regenerated by the build)
    ├── Scripts/main.lua      Commented map script
    ├── Vegetation/forest.json Example tree positions
    ├── docs/                 Guides for terrain, scripts and trees
    ├── README.md
    ├── preview.png
    └── workshop.json

create map generates a starter slope. It has not built your heightmap yet. Keep working from the parent SkiEO-maps folder for all commands below.

Checkpoint: the my-resort directory contains custom-map.json. If the directory already contains a project, choose a fresh output folder.

STEP 04

Describe your source in the JSON

Copy your chosen source file into my-resort/Terrain/. Open my-resort/custom-map.json in a text editor. The build object belongs at the top level, alongside metadata and terrain.

The generated project already has a build object for example trees. Replace that object with the selected block below for a first terrain-only test, or add heightmap inside the existing object to keep your manual forest. Use one build key. Leave the other top-level properties in place, with commas between them; JSON does not allow comments.

"build": {
  "heightmap": {
    "file": "Terrain/source-heightmap.r16",
    "spacing_meters": 8
  }
}

"build": {
  "heightmap": {
    "file": "Terrain/source-heightmap.png",
    "spacing_meters": 8
  }
}

"build": {
  "heightmap": {
    "file": "Terrain/source-heightmap.png",
    "spacing_meters": 8,
    "elevation_meters": [800, 2200]
  }
}

Paths are relative to my-resort and use forward slashes. Keep the source separate from Terrain/heightmap.r16: that filename is reserved for the generated terrain. Every build reads your original source again.

"elevation_meters": [800, 2200]

"height_scale_meters": 0.025,
"height_offset_meters": 724

Optional: bake erosion, green ground cover and trees

First build and test the original relief. Then add treatments without changing the source you selected above. The following values suit the practice terrain; adapt the biome to your own mountain and elevation range.

Add processing inside your existing build.heightmap, after its source settings. Keep its file, spacing and any dimensions or elevation encoding:

"processing": {
  "resolution": 513,
  "smoothing": {"iterations": 2, "strength": 0.15, "max_delta_meters": 1},
  "thermal_erosion": {"iterations": 8, "talus_degrees": 35, "strength": 0.2, "max_delta_meters": 3},
  "hydraulic_erosion": {"iterations": 4, "strength": 0.06, "rainfall": 1, "max_delta_meters": 1}
}

Copy

Add vegetation beside heightmap, inside the same build object. Separate sibling properties with commas:

"vegetation": {
  "biome": {
    "tree_line_meters": 1900,
    "alpine_line_meters": 2400,
    "temperature_sea_level_celsius": 15,
    "lapse_rate_celsius_per_km": 6.5,
    "moisture": 0.65,
    "wind_strength": 0.3,
    "wind_direction_degrees": 270
  },
  "trees": {
    "seed": 42,
    "density_per_hectare": 90,
    "min_spacing_meters": 5,
    "max_slope_degrees": 32,
    "tree_line_fade_meters": 150,
    "patch_size_meters": 160,
    "patchiness": 0.6,
    "max_trees": 100000
  },
  "ground_cover": {"texture_size": 256, "max_slope_degrees": 45}
}

Copy

If you are using the relative 0–1,000 m test range, start with a tree_line_meters of 900 and an alpine_line_meters of 1,100, then tune them after checking the result. Known real elevations let you use the actual tree line.

The complete practice preset is for the downloaded PNG. For your own heightmap, add the fragments above to your current settings so the source path stays correct.

What each setting changes

Setting	Effect
smoothing	Softens local relief. strength controls each pass; iterations repeats it.
thermal_erosion	Moves material downhill where the slope exceeds talus_degrees.
hydraulic_erosion	Uses steepest-descent drainage and contributing area to move material downhill. rainfall is a dimensionless multiplier.
max_delta_meters	Bounds the total height change per vertex for that treatment, across all its iterations. Budgets from different treatments can add together.
resolution	Limits processing to 513 vertices on the longest axis here. Larger inputs retain fine source detail while receiving interpolated corrections. Allowed: 33–1025.
tree_line_meters, alpine_line_meters	Upper altitude for trees and green ground cover. The alpine line must be higher than the tree line.
Temperature, moisture and wind	Control static growth suitability. Moisture and wind strength range from 0 to 1. Wind comes from the specified compass direction: 0 north, 90 east, 270 west.
density_per_hectare, min_spacing_meters	Control candidate density and tree separation. Habitat filters reduce the actual tree count.
max_slope_degrees, tree_line_fade_meters	Exclude steep ground and thin the forest as it approaches the tree line.
seed, patch_size_meters, patchiness	Give reproducible forest patches. Use another seed for a different arrangement.
max_trees	Caps the forest. At the cap, the build retains a seeded uniform subset across the map.
ground_cover.texture_size	Resolution of the grass/rock albedo. Use a power of two from 16 to 512; the build supplies all mip levels and the material mapping.

These are bounded terrain-authoring approximations. They do not reproduce the official developer’s complete erosion and climate bake. Drainage does not fill depressions or create rivers. Wind affects vegetation exposure; weather and snow remain managed by the game. Ground cover is grass/rock colour on the terrain, not 3D grass blades.

The drainage routing follows the D8 steepest-descent principle; thermal erosion uses a critical slope, a common heightfield modelling technique. The implementation and budgets here are specific to these community tools.

Disable a treatment or add fine detail

Omit an individual processing method to disable it; omit processing for the original relief. Add "noise": {"amplitude_meters": 0.25, "wavelength_meters": 64, "seed": 42} inside processing for reproducible detail. The wavelength must span at least two processing grid intervals. The boundary is preserved.

Use "enabled": false inside trees or ground_cover to disable that component. Removing vegetation restores the authored terrain material. With automatic trees off, any configured build.forest supplies the manual forest; otherwise the generated forest is empty.

Reserve a clearing or place trees manually

Add "exclude": [[-60, -40, 60, 40]] inside trees to keep a 120 × 80 m clearing around the centred origin. Each rectangle is [west, north, east, south] in world metres: X east, Y south. min_elevation_meters can also set a lower altitude limit.

For manual trees, keep "forest": {"file": "Vegetation/forest.json"} alongside heightmap inside build and edit the source array of {"x": 10, "y": -20} points. Automatic trees take precedence when enabled. The build converts manual JSON to SKXY float32 centimetres; automatic trees are written directly in SKXY. The game reads only the compiled binary. JSON is an authoring format.

Inspect Terrain/Generated/build-report.json for height-change and tree-count statistics, Terrain/Generated/albedo.png for ground colour, and Vegetation/Generated/ground-cover.png for the growth mask. The forest is Vegetation/Generated/forest.skxy. Generated rendering overrides and the importer entry point live in the package; your original script and manual JSON remain editable.

Checkpoint: the JSON points to your chosen original source, with spacing and any known dimensions or altitude encoding. No separate import or conversion command is required.

STEP 05

Build and validate the map

From the parent SkiEO-maps folder, run:

skieomod build my-resort
skieomod test my-resort
skieomod test my-resort/bin/author.my-mountain-0.1.0.skieomap

Check the terrain summary before launching the game. Its dimensions and extent must match your source, rather than the starter slope. The heightmap path and settings come from the JSON. If you chose another ID, substitute it in the last filename. A successful build creates my-resort/bin/author.my-mountain-0.1.0.skieomap.

Terrain: 513 x 513 samples; 4096 x 4096 m; 800 to 2200 m elevation; portable R16LE

Without altitude settings, the summary shows 0 to 1,000 m and explains that real altitudes are unknown. Any square-grid assumption is also printed and saved in Terrain/Generated/build-report.json.

The build updates terrain.source, size_meters, elevation_meters, the centred origin and preview.samples in your project JSON. It writes the generated terrain to Terrain/heightmap.r16 and backs up the replaced manifest and terrain under .heightmap-backups/. The original source-heightmap.png or source-heightmap.r16 stays intact.

You can inspect the calculated values after building, but you do not need to enter them. The package contains the portable R16, map metadata, script and referenced resources; the development-only build section and original PNG are omitted. The loader constructs the terrain in the game.

test my-resort checks a freshly prepared package using the same JSON settings without changing the source project. Validation does not prove that the slopes, snow or gameplay feel right. If you change Lua scripts, install Lua 5.4 and additionally use skieomod test my-resort --check-scripts.

Checkpoint: the terrain summary matches your source, and both the project and the exported archive are reported as valid.

STEP 06

Try the terrain in Ski-E-O!

Close the game, then run:

skieomod run my-resort

run rebuilds your project, installs it into the saved map directory and opens the game through Steam. If the map selection screen appears, choose New Game → Custom Map → My Mountain. Use a new session to check the imported terrain before working with an existing save.

• Move around the terrain. Check that ridges and valleys face the expected directions.
• Check the elevation readout at a known high or low point. A recognisable shape can still have the wrong scale.
• Try a trail, building placement and snow tools to check the surface and collision.
• Inspect tree roots up close and check forest coverage across the full map, including both ends of rectangular terrain. Forests follow the biome, elevation and slope limits.

The optional bake supplies green ground cover and trees. A heightmap still does not specify ski lifts, buildings or a complete resort; add those after the terrain behaves correctly. Start a new session when comparing build settings.

Checkpoint: you can start a session on your terrain, with the intended size, elevation and orientation.

STEP 07

Keep the project, share the package

Send the file in my-resort/bin/ to a tester who has Custom Map installed. They can copy it to their maps_dir and select it in the game. Keep the source project so you can edit and rebuild the map later.

Before sharing your own map, update the name, description, authors and licence in custom-map.json. Credit your elevation data provider and respect its redistribution terms. For a new release, increase metadata.version (for example, 0.1.0 to 0.1.1) and build again. Keep the map ID stable.

Workshop preparation is a later step: skieomod publish my-resort --prepare stages an unpacked article, but it does not upload it. Actual publication requires the game’s Workshop integration and a native Steamworks client. You can share the local .skieomap while that integration is unavailable.

WHEN SOMETHING LOOKS WRONG

Troubleshooting

The build accepts up to 32 MiB of raw samples and 16,384 samples per axis. For larger inputs, resample in your terrain tool first. World extent is not capped at 8 km; choose spacing and rendering detail to suit the size of your map.

Where to go next

Your project’s docs/terrain.md, docs/vegetation.md and docs/scripting.md explain the terrain format, tree positions and Lua API. The terrain guide describes template defaults; the calculated terrain values written by your build describe your own map.

Project reference: getting started, CLI documentation and map format specification. The versioned guide bundled with your installed tools contains the matching release documentation.