Feature: STL Tiles

Purpose

Printable 3D models of the Earth rendered from the GDEM data on the shared /datasets volume: the surface of the globe is divided into roughly equal-size tiles along lines of latitude and longitude, and each tile is rendered as an STL file that loads into a slicer (OrcaSlicer, PrusaSlicer) and prints on a 3D printer.

Requirements

• scripts/stl-tiles-build.sh must render the tile set into dataflow.out/stl/ from the ETOPO 2022 source tiles (/datasets/dataset-etopo-2022/, read-only).
• The globe surface must be divided into tiles along latitude and longitude lines; tiles in the same latitude band must have roughly equal surface area (longitude split scales by the cosine of the band’s mid latitude).
• The highest and lowest latitude bands must each be a single round tile (the polar caps, spanning the full 360 degrees of longitude).
• Each tile must have a flat bottom that sits against the printer bed; the STL’s z = 0 is the bed plane.
• Each tile must be a watertight solid (every edge shared by exactly two triangles), so slicers accept it.
• Each tile must mate with its neighbors along the top surface: the top surface is the spherical surface of the globe at radius R with elevation relief, and neighboring tiles sample the same geographic boundary.
• The side walls must be chamfered so each wall plane contains the globe center, so the walls of assembled neighbors are coplanar.
• Alignment keys: north and east walls carry vertical fins, south and west walls carry vertical grooves, polar-cap rings carry grooves; a fin is placed only when its mating groove exists, so every fin meets a groove in the assembled globe. The keys must be vertical (running from the top edge down the wall) so they print without supports.
• The underside must carry an engraved (recessed) tile id; z = 0 must stay the lowest plane.
• Elevation must be mapped with a global (not per-tile) range, so all tiles share the same absolute scale.
• Output format: binary STL, millimeters.
• scripts/stl-tiles-build.sh --check must validate every generated tile (watertight, flat bottom at z = 0, expected bounds, positive signed volume) without rebuilding.
• The build must write dataflow.out/stl/manifest.json: parameters, tile list with bounds and sizes, and provenance (dataset, script, timestamp, git commit).
• The build must support rendering a subset: --tiles <ids> (specific tiles) and --region <south> <north> <west> <east> (tiles intersecting a geographic region).
• Derived output (dataflow.out/stl/) is generated and must not be edited by hand.

Behavior

• Running the script recreates the tile set deterministically from the source tiles and the given parameters.
• Re-running the script overwrites existing tiles.

Dependencies

• Tool-gated: GDAL 3.8+ and Python 3 with the osgeo and numpy modules, plus the ETOPO source tiles under /datasets on the owning host.
• Dataset etopo-2022 maintained by the model-elevation-earth project.