Feat/osm dem - #55
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Feat/osm dem#55
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type = "osm" reads ways (roads, rivers, ...) by Overpass statements, clipped to
the grid plus a margin, and registers them as a vector source with checksum and
provenance, ready for the `distance` and `count` operators.
- The answer is cached by request (statements, bbox, date): a pipeline reads the
same bytes, hence the same spec_hash, on every run and workspace.
- `date` asks for an older snapshot ([date:"..."]); with `years`,
date = "{year}-07-01" gives one per year.
- Several public Overpass servers are tried in turn with retries; HTTP 406 stops
at once and points to OSM_CONTACT; an empty answer is an error and not cached.
- Provenance: request, server, time retrieved, timestamp_osm_base, features,
checksum, ODbL attribution.
- Tests run against a local fake Overpass server (no network); guide
docs/guides/osm.md.
Ports 02b_fetch_osm.py of lab15-reconstruction. Not exercised against the real
Overpass API (unreachable from the environment this was written in).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
…PODATA type = "dem" reads a digital elevation model over the grid (plus a margin) and registers elevation, or slope in degrees or percent, as a raster source with checksum and provenance, ready for the zonal operators. - dem = srtm | copernicus | topodata, or `tiles` with your own GeoTIFFs. Only the window over the grid is read (HTTP range requests for SRTM and Copernicus); TOPODATA sheets are downloaded once into $DISSCUBE_CACHE/dem. - Slope is computed in the source, because an operator does not see the neighbours of a pixel: bilinear to the UTM zone of the grid's centre at `resolution` metres, then central differences (numpy.gradient). - Voids and values outside -1000..9000 m become NaN. A tile that cannot be opened is skipped with a warning; none readable is an error. - Asking for a Copernicus slope logs a warning: GLO-30 includes the forest canopy, so slopes at forest edges are overestimated. - Tests use synthetic tiles (a plane of known slope, a gzip-ed HGT, a ZIP served by a local HTTP server); guide docs/guides/dem.md. Ports 02c_fetch_dem.py of lab15-reconstruction. Builds on the `osm` commit (same schema, runner and docs insertion points). Not exercised against the real tile servers (unreachable from the environment this was written in). Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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