nordisk/facett

facett-osm — crate card

Reverse-engineered (from source — verify, don't trust the name)

• One-line pitch: An OSM GeoParquet reader — decode osm2geoparquet/katana-osm WKB geometry into facett map points/ways.
• Does: decode_wkb parses a WKB blob (Point/LineString/Polygon, LE/BE, ignoring Z/M/SRID) into (lon,lat) vertices; reader functions (e.g. read_points/read_ways) stream a GeoParquet's geometry column via a parquet ParquetRecordBatchReaderBuilder and hand facett_map::Ways / points to MapView. Works from either an on-disk File or an in-memory bytes::Bytes (so the wasm demo can include_bytes! Sigtuna with no filesystem).
• Key deps: facett-map (Way), facett-core (Theme), arrow-array, parquet (arrow+zstd, no default features), bytes, serde_json.
• Shape: lib; tiny (single lib.rs).
• Observed role in the workspace: Re-exported by umbrella facett as facett::osm. How facett gets real OSM data (millions of points) for the map component + its tests; used by korp's map load from osm-katana GeoParquet.

Fill in (one line each — only the human knows these)

• Primary consumer(s):
• Why it exists (vs the obvious alternative):
• Hard constraint (airgap / no-C-deps / no-FFI / pure-Rust / etc.):
• Release cadence & independence (rides a parent? own repo someday?):
• Status (production / prototype / experimental / stubbed):
• Must-NOT-change invariant:
• Biggest known gap or TODO:
• Anything a newcomer would get wrong about it:

Coverage (nornir test matrix)

The one crate on the map hot path used to emit no functional cell. tests/testmatrix.rs now drives the whole decode pipeline in memory (via the _bytes readers — the filesystem-free path the wasm demo uses, so no osm2geoparquet binary is needed) and emits, behind the no-op testmatrix feature (--features testmatrix):

• facett-osm/nodes · decodes_wkb_points — N WKB Points → N (lon,lat) vertices;
• facett-osm/ways · classifies_area_vs_line — a water Polygon → filled area, a highway LineString → stroked line (the tag-driven split the basemap render keys on);
• facett-osm · headless_render — the reader produced non-blank drawable geometry (emit_render: decoded way vertices > 0 over a non-degenerate bbox), so a WKB-decode regression reddens the cell instead of silently blanking every downstream map;
• facett-osm/wkb · truncated_blob_does_not_panic — a clipped WKB header decodes to nothing without an out-of-bounds panic (guards the bounds-check fix 0b5f0a6).