AC Track Builder

Turn any real road into an Assetto Corsa track, in your browser. Search for a road, drop a start and a finish pin, press Build, and download a zip that installs straight into Content Manager.

It is a from-scratch take on what Street2Sim does (see docs/how-street2sim-works.md), but everything runs client-side: no server, no account, no queue.

What you get

• The real road, routed along the OpenStreetMap network between your pins (add pins in between to force a route, or tick Loop back to start for a circuit).
• The road traced from the aerial photos: where the asphalt can be seen, the road follows its real line and width (OSM is often a metre or two off); under tree canopy it falls back to OpenStreetMap. Where the trace goes wrong, a "No-trace zone" on the map keeps the mapped line there.
• Line markings read off the photos (lane lines, edge lines, dashed or solid, in phase with the real ones), generated from sight distance where the photos can't show them.
• Optional photo road surface: each stretch of road textured with its own aerial photo (cars and paint removed, shadows evened, fine grain added).
• Real elevation from open terrain data, smoothed along the road, with a 2% crown and banking in corners.
• Road width from OSM width / lanes / road class, or a width you choose.
• Asphalt with edge lines and a dashed centre line, gravel verges, and terrain each side of the road textured with aerial imagery.
• Kerb and gutter in town: a concrete gutter, a 150 mm kerb (its own physics surface, mountable but felt) and a nature strip textured from the aerial photo, so footpaths and driveways show. Out of town only where the photo clearly shows one. Kerbs curve round the corners into side streets and carry on along them for 40 m, and roundabouts in town get a kerbed ring too, open wherever a road joins it. A kerb never stands on drivable road.
• Low-detail horizon terrain out to 1.5 km so the world doesn't end at the roadside.
• Australian road surfaces: chip seal on rural roads, dense asphalt on major roads and in town, with wheel-path wear, patch repairs and sealed cracks.
• Line markings as real geometry: white edge lines, and a dividing line that is broken where there's overtaking sight distance and becomes a barrier line on blind bends and crests, plus raised pavement markers.
• Real roundabouts: the full circulating carriageway, a mountable kerb and a planted island, instead of a hairpin where the route goes round one. Give-way lines across each entry, and on two-lane roundabouts (from the OSM lanes tag, or a ring wider than 9.5 m) a wider ring with a lane line round it.
• Side streets: the other roads around the route are drawn too, joined to it at proper junction mouths (motorways, bridges and tunnels are left out).
• Street name signs (white on blue blades) at every named junction, plus signs for shops, servos, schools and landmarks, bus stops with shelters and servo canopies, from OpenStreetMap.
• Street-level detail from Mapillary (optional, free token): real traffic signs (speed limits, give way, stop, warnings, chevron alignment markers), power poles, street lights, traffic lights, stop lines, zebra crossings, turn arrows (centred in their lane, facing their traffic) and painted speed numbers where its photos found them.
• Sharper aerial imagery from the Queensland and NSW governments where available (up to 0.1 m/px), falling back to Esri elsewhere. NSW imagery is colour-matched to Esri's at the zoom in use, as some of its surveys carry a strong blue haze.
• Bare-earth elevation from the Queensland, NSW and Victorian government models (lidar where captured) instead of SRTM, which measures the tree tops.
• Scenery: trees wherever the aerial imagery shows tree canopy, guard rails where the ground drops away beside the road (or where OSM maps one), white guide posts, and buildings: OSM footprints where mapped, plus placeholder houses wherever the imagery shows a roof, with Colorbond or terracotta roofs in the matching colour. In built-up areas every street frontage is read from the photo too, so each lot gets its house, square to the street at the setback and depth the photo shows.
• A wide range of building types, each with its own walls, windows and roof: brick veneer, weatherboard, fibro and rendered or clad modern houses (some two-storey, some with skillion roofs); Queenslanders on stumps behind lattice, with a verandah and deck (in Queensland); townhouses, brick walk-up flats and apartments with balconies; glass towers; offices; shops with a shopfront, sign, parapet and awning over the footpath (shops under the flats and offices on main streets); warehouses and sheds in Colorbond or tilt-up concrete with a roller door; brick churches, halls and schools. About 60 wall finishes and 20 roofs (Colorbond colours, terracotta and concrete tiles, membrane and gravel). The type comes from what's known: OSM's building type and height, a shop, cafe, church or school mapped inside it, the roof colour in the photo, its size and whether it fronts the street. Only the finishes a track uses go in its file.
• Race-day dressing (Race day in the options): the start/finish straight and the outside of each tight corner are dressed like a street circuit on race weekend. Concrete barriers with a debris fence on top and sponsor banners along it, wraps on the concrete, tyre walls through the corners, an overhead start gantry with lights (a chequered one at a separate finish), a grandstand full of people where there's room, spectators along the fence, feather flags, and marshal posts with flags. Side streets stay open, and the rest of the street is left as it is. Sponsors are an editable list of names, drawn as text in each brand's colours (known Australian motorsport brands get theirs). Real names are fine for your own use; if you share a track publicly, consider made-up ones.
• Invisible walls that keep you on the road and pull in where switchbacks pass close to each other.
• Time trial ready: on an A-to-B road the timed section is exactly the road between your pins. A run-up is added before the start pin (the grid, plus room for a flying start in Hotlap mode) and a 150 m run-off after the finish pin, along the real streets where they carry on. The start line is painted across the road and the finish line is chequered, with START and FINISH signs each side. Side streets and grass are off track, so cutting through them invalidates the run. "Back to pits" or "Restart" puts you on the grid 8 m behind the line. Loops get a start/finish line instead.
• Pit boxes, a starting grid, a hotlap start and an AI line (fast_lane.ai).
• Content Manager extras: ui_track.json with name, length, geotags and country, an outline, a preview render, and the in-game map.

Running it

npm install
npm run dev        # http://localhost:5173
npm test           # format round-trips + a full synthetic build
npm run build      # static site in dist/, host it anywhere

The page keeps your road in its address: the pins, no-trace zones, track name and any settings you changed. Reloading brings it back, and Copy link gives a link that reproduces the build (your Mapillary token is never in it).

Installing a track

Drag the downloaded zip onto Content Manager and click Install, or unzip it into steamapps/common/assettocorsa/content/tracks/. The zip contains one folder (<track>/ with ui/, data/, ai/ and the .kn5), so nothing ends up nested too deep.

Making it look its best in game

The track works in plain Assetto Corsa. The ground is the aerial photo, which is a blur up close (30 cm a pixel at best), so with Detail shaders on (the default) it carries tiling grass, dirt and paving detail as well, picked per spot from the photo's colour: the photo gives the colour, the detail the close-up texture, as on hand-made tracks.

With Custom Shaders Patch (CSP) it also reads the track's extension/ext_config.ini, so turn these on in CSP's settings:

• Lighting FX: the street lights light the road at night, lanterns glow, house windows show lit rooms, and a built-up area glows on the skyline.
• Grass FX: real grass blades on lawns and nature strips near the car, where the aerial photo alone is a blur.
• Rain FX: puddles and soaked asphalt, darker concrete, slippery paint.

Ambient occlusion makes the biggest single difference to how solid a scene looks (soft shadow where walls meet the ground, under eaves, along kerbs), and CSP expects tracks to have it. It is baked per track on your PC with CSP's vertex AO bakery (runs on any hardware: on the CPU, or the GPU on recent cards): put the track in content/tracks and run the bakery on its .kn5.

If the road or the ground looks wrong up close (too dark or bright, shiny or black), untick Detail shaders and build again: that goes back to plain textures.

How a build works

pins ──OSRM──▶ route polyline ──▶ local metres (scaled Web Mercator)
                                   │
  Overpass (widths, rails, buildings) ─┤
                                   ▼
                     smoothed centreline, sampled every 2 m
                     width · banking · crown
                                   │
        Terrarium elevation tiles ─┤──▶ smoothed height profile
                                   ▼
   road ribbon · verges · terrain grid (blended into the road) · walls
   horizon terrain · spawn/timing dummies · AI line
                                   │
           Esri aerial tiles ──────┤──▶ one DXT1 .dds per 200 m chunk
                                   ▼
            .kn5 + fast_lane.ai + data/ + ui/ + map.png ──▶ zip

Path	What it does
src/core/kn5.ts	.kn5 writer and reader (textures, materials, node tree)
src/core/aiSpline.ts	fast_lane.ai v7 writer and reader
src/core/dds.ts, png.ts	DXT1 DDS and PNG encoders
src/core/geo.ts	Local projection that lines up exactly with web map tiles
src/core/road.ts, polyline.ts	Centreline smoothing, widths, banking, nearest-point index
src/core/roadMesh.ts	Road, verge and wall meshes
src/core/terrain.ts, backdrop.ts	Drivable terrain corridor and horizon scenery
src/core/scenery.ts	Trees from imagery, guard rails, guide posts
src/core/buildings.ts	OSM footprints and roofs detected in imagery; walls, roofs (hip, gable, skillion, flat behind a parapet), verandahs, awnings, doors
src/core/buildingStyles.ts	Building types, facades (walls and window layouts) and roof finishes, and the textures painted from them
src/core/frontage.ts	Houses read off the photo along each street frontage
src/core/markings.ts	Edge and dividing lines from sight distance, pavement markers
src/core/sideStreets.ts	Other streets near the route and their junctions
src/core/furniture.ts, art.ts	Street name signs, landmarks, bus stops, Mapillary objects; the sign artwork atlas
src/core/trace.ts	Road line and width traced from the aerial photo
src/core/paintLines.ts	Line markings read off the aerial photo
src/core/photoSurface.ts	Photo road surface textures
src/core/kerbs.ts	Where kerbs are (photo evidence and how built-up it is), kerb, gutter and nature strip meshes
src/core/roundabout.ts

src/core has no DOM or network code, so the whole pipeline runs under Node in the tests with synthetic terrain.

Data sources and licences

• Roads and buildings: © OpenStreetMap contributors, ODbL, via Overpass and OpenFreeMap vector tiles. Routing by the public OSRM demo server; place search by Photon and Nominatim.
• Elevation: Terrain Tiles on AWS Open Data (SRTM, USGS 3DEP, GMTED and national lidar where available).
• Elevation in Queensland, NSW and Victoria: the State of Queensland's bare-earth Queensland Digital Elevation Model (0.5 m lidar where captured) and NSW Spatial Services' 5 m elevation, used instead of the tiles there because SRTM-based tiles include the tree canopy. In Victoria, the Vicmap Elevation 10 m DEM (c) State of Victoria, decoded with Esri's lerc.
• Aerial imagery: Queensland Government and NSW Spatial Services imagery where available, else Esri World Imagery.
• Street-level detections: Mapillary, CC BY-SA, with your own client token. Fine for building tracks for yourself; don't publish or sell tracks that contain it. Pick Aerial imagery → Off for a track you want to share, and it uses a procedural grass texture instead.

The public OSRM, Nominatim and Overpass servers are free community services with fair-use policies. They're fine for personal use. If this ever gets real traffic, run your own instances or use a paid provider.

Assetto Corsa is a trademark of Kunos Simulazioni. This project is not affiliated with or endorsed by Kunos.

Status

Every file format is cross-checked against Content Manager's and AssettoServer's readers and round-trip tested, but nothing has been loaded in the game yet. docs/verification.md is the checklist for the first in-game test, and docs/roadmap.md lists what comes next.