Props & structures

A world generated from map data can feel strangely empty: the marina has water but no boats, the construction site is a gravel rectangle, the wind farm is a field. Props fix that. Since Meld 1.6.0 (Arnis fork 3.0.1), the generator ships a set of pre-built 3D models and stamps them where the map actually says they belong.

Why props are placed, not generated

Buildings can be generated from their footprints, because OSM records the footprint. A crane or a tractor has no footprint to extrude; the map only records that something is there (a construction site, farmland, a wind generator node). So props are hand-built schematics, bundled with the generator, placed at the features that imply them. Because they are pre-built, props are fixed-size: they do not shrink with your world’s scale, which is why they are gated at small scales (more below).

How it works

The families

Props come in families, each tied to a real OSM feature and each with its own toggle:

• Boats on open water
• Parked cars in car parks (sedans, SUVs, pickups, vans and friends)
• Cranes and excavators on construction sites
• Tractors on farmland
• Wind turbines at mapped wind generators
• Lighthouses at lighthouse features
• Fountains, playgrounds and cemetery tombstones at their amenities

There is also one landmark easter egg for those who go looking. A family that is off costs nothing: no extra render time, no extra RAM. Placement is seam-audited like everything else in the fork, so a prop never straddles two cells disagreeing about it; one prop (a parked helicopter for helipads) is deliberately deferred until it can be placed seam-safely, and the fork’s changelog says so rather than shipping it broken.

The scale gate

Because props are fixed-size, a scaled-down world does not scale them: at 1:10 a crane would tower over a whole district. The generator therefore skips props below scale 0.35 by default (the fork’s --props-min-scale). This used to be a silent trap (ten ticked checkboxes and no boat anywhere), so Meld now warns you the moment a project’s scale falls below the gate, and gives you the prop scale control to move it (0 places them at any scale, at your own aesthetic risk). See Choosing a scale for the other things that change with scale.

Quality control

Every bundled model is swept by a validity check, and a corrupt schematic fails loudly by name instead of stamping garbage in the wrong place. The system also self-corrects over time: an early 3D stadium model kept landing on ordinary neighbourhood football fields, so Arnis 3.0.10 removed that archetype outright, keeping the painted pitch lines and goals. Props are meant to appear where they belong or not at all.

How to use it

1. Open Settings and the Props & 3D models drawer. Schematic props and downloaded 3D models sit inside as labelled groups.
2. Tick the families you want. Omitting the choice keeps every family on; the fork’s CLI equivalent is --props all|none|<list>.
3. Check your scale. At 1:1 everything places; below 0.35 nothing does unless you lower the gate, and Meld will show the warning either way. The bundled Scaled 1:10 preset ships with props off for exactly this reason.
4. Generate. Boats appear in the harbour, turbines on the ridge, tombstones in the cemetery, all driven by the data, so a place with no mapped marina gets no boats.

Props pair well with the rest of the world-detail stack: Farmlands & crops fill the fields the tractors sit in, Region tree packs handle the vegetation, and The Arnis fork page covers the engine all three live in.