flatland — the geometric city layer
Public quest. A 3D city built from OpenStreetMap data — buildings, roads, ground — that gives the places in Rohan's world a real base, real edges, and a real skyline. It is the layer under the splats, not a replacement for them.
Name: from Edwin Abbott's Flatland (1884) — a world of pure geometry, viewed from the wrong number of dimensions. Ours is the flat, extruded, honest skeleton that photoreal splats get dropped onto.
Why it exists
Rohan, 2026-10-07, after finding cartesiancs/map3d and the viral campus reconstruction at https://mount-alison-3d.vercel.app/:
"I think it might help to have multiple layers… maybe we get some Frankenstein in-between viewer with white OpenStreetMap geometric basic layer, then we can add splats on top."
Three jobs, in order of how real they are:
| job | what it means | honest verdict |
|---|---|---|
| 1. Presentation base | real ground, streets and skyline behind and under the splats; the viewer stops being a model floating in black | ✅ doable now — one three.js scene, OSM extrusions + splat overlays |
| 2. Geo-reference and scale | match captured facades to their OSM footprints → solve the splat scene's arbitrary SfM scale and place it on the real map | ✅ doable — footprints + a rigid fit; this is how splats get coordinates |
| 3. A principled floater filter | cull splats that fall outside any building footprint or above its recorded height | ✅ doable — OSM gives the envelopes |
| feed the city geometry into Brush so it shapes the Gaussians | ❌ not available — 3DGS trainers take no mesh prior; don't spend time here |
Scope
- Public by construction. Only exteriors and places visible from public streets — the park, the block, the facade. No interiors, no personal data (the apartment's inside stays in the private apartment quest and the GLB viewer).
- Candidate areas: 348 W Wendell St (his block) · Washington Square Park (Chicago) · LaSalle / Oak streets · the downtown drive route. All locations he has 360 footage for, so splats can be layered on when they land.
- Data: OpenStreetMap (ODbL — attribution required when published) → building footprints +
heights + street centrelines. Generation options:
map3d(React-Three-Fiber, GLB export, MIT) or a small Overpass + extrusion script of our own that emits GLB/GeoJSON directly.
Deliverables
- A generator: bounding box → OSM query → extruded buildings + roads → GLB (plus a JSON of footprints/heights for the culling work).
- A viewer: the same three.js shell as the apartment page, with the flatland layer as the base and toggleable splat overlays — the "frankenstein" viewer.
- Geo-referencing notes: how a splat scene gets placed onto the layer (footprint-to-facade fit, scale solve, then a 4×4 transform baked at publish time).
Status
Filed 2026-10-07 (Rohan's call: public, no interiors). Nothing built yet.
Sources
github.com/cartesiancs/map3d(R3F, OSM → 3D buildings/roads, GLB export, MIT) ·mount-alison-3d.vercel.app(the campus demo that prompted this)wiki/apartment-3d.md(the places registry this layers into) ·wiki/splat-pipeline.md(the splats that go on top) ·inventory/splat-workspace.md(map/in the DAS workspace)