BEGIN:VCALENDAR VERSION:2.0 PRODID:-//pretalx//talks.osgeo.org//foss4g-2026//talk//RP9FQJ BEGIN:VTIMEZONE TZID:JST BEGIN:STANDARD DTSTART:20000101T000000 RRULE:FREQ=YEARLY;BYMONTH=1 TZNAME:JST TZOFFSETFROM:+0900 TZOFFSETTO:+0900 END:STANDARD END:VTIMEZONE BEGIN:VEVENT UID:pretalx-foss4g-2026-RP9FQJ@talks.osgeo.org DTSTART;TZID=JST:20260901T130000 DTEND;TZID=JST:20260901T133000 DESCRIPTION:Problem Statement\nOpen 3D city model datasets are becoming inc reasingly available worldwide through standards such as CityGML. In Japan\ , the Ministry of Land\, Infrastructure\, Transport and Tourism (MLIT) has released Project PLATEAU\, one of the largest national open 3D city model initiatives\, covering over 200 municipalities with building\, terrain\, vegetation\, and infrastructure data at multiple Levels of Detail. However \, while PLATEAU provides official SDKs for proprietary game engines (Unit y\, Unreal Engine)\, no documented workflow exists for integrating PLATEAU data into open-source interactive environments. More broadly\, the geospa tial community lacks a fully documented\, reproducible pipeline for transf orming CityGML data into lightweight\, interactive 3D applications suitabl e for deployment on low-specification hardware typically found in schools or community centres where participatory planning workshops take place.\n\ nThis paper presents and evaluates a complete open-source pipeline from Ci tyGML acquisition to interactive real-time 3D environment\, using exclusiv ely free and open-source software: Blender for geospatial data processing and 3D optimisation\, and the Godot Engine for real-time rendering and int eraction. We validate this pipeline through deployment in a participatory urban design workshop with elementary school students in Yokohama\, Japan. \n\nPipeline Architecture\nThe pipeline comprises four stages.\nStage 1: D ata Acquisition. CityGML data for the target site (Takashima Central Park\ , Minato Mirai\, Yokohama\; approximately 113 m x 159 m) was downloaded fr om PLATEAU's open data portal\, including buildings\, terrain\, vegetation \, and infrastructure at LOD1 and LOD2. The LOD selection involves a criti cal trade-off: LOD2 provides roof shapes and facade detail but substantial ly increases polygon count. A selective strategy was adopted\, retaining L OD2 for buildings within the workshop perimeter and simplified representat ions for surrounding context.\n\nStage 2: Conversion and Optimisation in B lender. CityGML data was converted to Blender-compatible formats (FBX\, gl TF). This stage involved coordinate reference system alignment\, geometric cleaning (degenerate faces\, inverted normals\, non-manifold geometries)\ , mesh simplification balancing fidelity with rendering performance\, sema ntic layer structuring (terrain\, buildings\, vegetation\, public space)\, and removal of elements beyond the perimeter. The processed model was exp orted in glTF to preserve coordinate alignment with the Godot engine.\n\nS tage 3: Integration in Godot. The optimised model was imported into the Go dot Engine (version 4.x). A critical step at this stage was the automatic generation of collision shapes for all CityGML-derived meshes (buildings\, terrain\, infrastructure)\, a requirement absent from GIS workflows but e ssential for game engine navigation: without collision data\, the first-pe rson character controller would pass through walls and terrain. A custom p lugin system was then developed\, comprising: a drag-and-drop asset placem ent interface sourcing 94 curated 3D objects from the Kenney asset library (CC0 licence) across six functional categories\; a first-person character controller for pedestrian-scale navigation over the collision-enabled env ironment\; and an embedded GDScript-based logging system that records ever y placed asset's identifier\, category\, position (X\, Z)\, and bounding-b ox volume as CSV files suitable for post-hoc geospatial analysis.\n\nStage 4: Deployment. The environment was packaged as a standalone Godot project deployable on standard educational PCs without dedicated graphics hardwar e\, requiring stable frame rates and responsive interaction under classroo m conditions.\n\nTechnical Challenges\nThe CityGML-to-game-engine conversi on raises several challenges that deserve documentation for reproducibilit y.\nCRS handling. PLATEAU metric coordinates produce models offset by larg e values from the scene origin when imported directly. A re-centring step in Blender was necessary to preserve internal metric distances while ensur ing that coordinates extracted from Godot remain mappable to real-world po sitions.\nConversion artefacts. CityGML-to-FBX/glTF conversion introduced flipped normals\, Z-fighting on coplanar surfaces\, and disconnected mesh fragments\, requiring manual inspection and correction. Documenting these artefacts and solutions reduces the barrier to entry for future pipeline u sers.\nLOD and performance. Full LOD2 for all buildings exceeded classroom -grade PC rendering capacity. The selective LOD strategy maintained intera ctive frame rates while preserving spatial realism sufficient for particip ants to recognise the site. Quantitative performance characterisation (pol ygon counts\, frame rates\, memory usage) will be reported in the full pap er.\nNo official Godot SDK for PLATEAU. Unlike Unity and Unreal\, Godot la cks a PLATEAU SDK. Blender proved essential as simultaneous format convert er\, geometry optimiser\, and semantic structurer\, positioning it as the key bridge component in any open-source CityGML-to-game-engine pipeline.\n Collision generation. CityGML meshes are designed for visualisation and sp atial analysis\, not for physics-based interaction. Game engine navigation requires collision shapes that prevent characters from passing through ge ometry. Automatic collision generation from imported meshes proved effecti ve for terrain and building shells but required verification for complex o r thin geometries where collision approximations could produce unintended barriers or gaps.\n\nValidation\nThe pipeline was validated through a part icipatory workshop conducted on 17 December 2025 at an elementary school i n Yokohama\, with approximately 50 sixth-grade students (aged 11-12) worki ng in 12 groups on six classroom PCs. Over two 45-minute sessions\, partic ipants placed 1\,192 assets without system failures\, demonstrating the pi peline's robustness under real deployment constraints with non-expert user s. The embedded logging system successfully generated coordinate-stamped d ata for all groups\, confirming that Godot's scripting capabilities can se rve as a lightweight geospatial data collection layer. Detailed evaluation of pedagogical and spatial outcomes is reported in companion publications .\n\nContribution\nThis work makes three contributions to the open-source geospatial community. First\, it provides the first documented end-to-end workflow for integrating CityGML/PLATEAU data into the Godot Engine via Bl ender\, filling the gap left by the absence of an official SDK. Second\, i t demonstrates that a fully open-source stack (PLATEAU + Blender + Godot + Python) can deliver interactive 3D urban environments on low-specificatio n hardware\, removing both licensing and infrastructure barriers. Third\, it shows that GDScript can serve as an embedded geospatial data collection tool\, producing coordinate-stamped logs amenable to standard GIS analysi s.\nThe pipeline is fully reproducible: all software is free and open-sour ce\, the PLATEAU data is publicly accessible\, and the asset library is CC 0-licensed. The methodology is transferable to any context where CityGML d ata is available\, including European national mapping agencies and the em erging OGC CityGML 3.0 ecosystem.\nFuture work will focus on automating th e Blender processing steps through scripted add-ons\, benchmarking the pip eline across different PLATEAU municipalities and LOD configurations\, and developing a standardised Godot plugin for direct CityGML import. DTSTAMP:20260717T225803Z LOCATION:Cosmos1 SUMMARY:From CityGML to Game Engine: A Reproducible Open-Source Pipeline fo r Interactive 3D Urban Environments Using PLATEAU\, Blender\, and Godot - Léo Martial URL:https://talks.osgeo.org/foss4g-2026/talk/RP9FQJ/ END:VEVENT END:VCALENDAR