Live browser QA of the Wind layer surfaced several rendering defects that
unit tests with fakes did not catch:
- The trail fade used a translucent black fill (source-over), which raises
alpha instead of erasing; combined with additive strokes the overlay
saturated into a solid white disk. Fade with destination-out instead, and
draw strokes with normal blending.
- Particles were seeded uniformly over the whole globe, so at regional zoom
almost none fell on screen. Seed inside the camera's visible rectangle.
- A non-finite particle position (polar divide-by-zero) reached Cesium,
which threw and aborted the entire frame before any stroke. Guard finite
coordinates per particle and per projection.
- Exaggerate advection in proportion to camera height, so the same visual
speed is legible at street level and at hemispheric zoom.
- Brighter colour ramp (the old ramp started near-invisible dark grey) and a
defensive frame try/catch so one bad frame cannot kill the loop.
Verified: the wind field/colour/particle model renders the real GFS 06z field
correctly in an offline render, and the wind unit tests pass (8/8).
Add a Wind layer animating the global 10 m wind field from NOAA GFS.
The /api/wind proxy selects the latest available 0.25° cycle, reads its .idx
inventory, byte-range fetches only the UGRD/VGRD 10 m GRIB2 messages (~1 MB
each instead of the whole ~500 MB file), decodes them with ecCodes (WASM),
resamples to a compact grid (1° default), and serves a manifest plus a Float32
U/V payload cached per cycle for an hour (single-flight, last-good on failure).
The client renders nullschool-style particles in a canvas overlay: bilinear
field sampling with longitude wrap, per-frame advection, Cesium camera
projection, and globe-occlusion culling via EllipsoidalOccluder.
Validated end-to-end against the real 2026-09-14 06z cycle on Node 25
(180x91 grid at 2°, 131,040-byte payload, plausible mean |u|/|v|). The WASM
decoder requires Node >=24, which the repo already requires.
Registered as `wind` (token k) with attribution and docs. Verified: npm test
(3412 pass, 0 fail), npm run check:boundaries.
Gustavo Beneduzi