Ratatoskr/scripts/ridge-bake

ridge-bake

Offline baker for the ridge backdrop: it turns a Copernicus DEM into six sun frames of three transparent WebP planes (far, mid, near) per place, plus a manifest.json and an index.json that the runtime reads. The baker is not shipped; public/ridge/ holds its output.

Run

python3 -I scripts/ridge-bake/export.py <place-id> --tiles DIR --out public/ridge/ [--work DIR] [--sheet contact.png]

Needs Python 3 with numpy, tifffile and imagecodecs. --tiles is a directory of Copernicus GLO-30 tiles (never committed); --work caches the mosaic and rays (default $TMPDIR/ridge-bake-work); --sheet writes the six frames over one flat sky. python3 -I scripts/ridge-bake/export.py --write-schema rewrites ridge-bake.schema.json; export.py holds the one dict it comes from.

Tests: RIDGE_PY=<python> RIDGE_TILES=DIR scripts/ridge-bake/tests/run.sh [test_ridge.py|mutate.py|mutate_export.py] (the full file takes about 9 minutes; mutate.py runs the mutants of taper, chains and sweep and mutate_export.py those of the planes path and export, each failing if one survives).

Tiles per preset (places.json, date 2026-09-23)

Files are Copernicus_DSM_COG_10_<N|S>dd_00_<E|W>ddd_00_DEM.tif; the list below is <N|S>dd<E|W>ddd.

place id	tiles
vienna	N47E015 N47E016 N47E017 N48E015 N48E016 N48E017 N49E015 N49E016
matterhorn	N45E007 N45E008 N46E007 N46E008
fuji	N34E138 N34E139 N35E137 N35E138 N35E139
halfdome	N37W121 N37W120 N38W120
amadablam	N27E086 N27E087 N28E086 N28E087
trecime	N46E011 N46E012

Planes

relight_planes renders every layer twice, with haze colour 0 and 1; the relight is affine in the haze colour, so the difference is each pixel's haze share. That share becomes transparency and the sky behind supplies the haze. Far is slot 0 plus the floor, near is the last slot, mid is every slot between (a place needs at least 3). Colour is exact over the frame's own haze colour; over another sky it drifts by the difference between the two. Stacked planes would leak: each plane's haze is alpha over whatever is behind it, so a nearer plane's haze would veil the farther ridge instead of the sky, and the farther ridge would show through it (a slanted seam through Vienna's near plane). relight_planes therefore scales a farther plane's alpha, near to far, to what the nearer layers leave open in the opaque frame (their transmittance over the stack's), looked up as the most open pixel within OCCLUDE_MARGIN_PX columns and eased by a Gaussian, because the runtime slides the planes against each other and a hidden pixel must stay hidden after the slide. The nearest layer is the ground in front of the eye: bake_layer(near=True) keeps its body opaque down to the horizon (its dissolve starts there), where the farther layers keep theirs (the haze arches). export.check_near_cover refuses, at write_bake, a near plane with a fully transparent column or a hole between a column's crest and the horizon row, in every frame; the farther planes may have empty columns. Over a flat sky the stack differs from the opaque frame by 1.8/255 over the whole frame (Vienna noon; 4.9 before the knock-out), but that is 11.2/255 mean over the 16.4% of pixels where two planes overlap and 0.005/255 everywhere else; the tests bound the frame at 3/255 and the overlap at 12.5/255. The spec's 2/255 pin is met on the frame; the overlap keeps the margin's soft blob.

Manifest luma is the min and max relative luminance (WCAG, linear 0..1) of the three planes composited far, mid, near over a flat mid-grey sky, over the pixels whose composite coverage 1 - prod(1 - alpha) is at least 0.5. No plane pixel is opaque (haze is alpha), so no per-plane solid set exists; the composite is what the runtime shows.

Licence

Elevation: Copernicus DEM GLO-30. The credit line is written into every manifest (attribution) and must be shown with any rendering:

Contains modified Copernicus data: DEM © DLR e.V. 2010-2014 and © Airbus Defence and Space GmbH 2014-2018 provided under COPERNICUS by the European Union and ESA; all rights reserved.

Licence: free, full and open access, with the credit line shown (https://spacedata.copernicus.eu/collections/copernicus-digital-elevation-model).