**Note** from Bead: Fire Progression · [canonical source](https://redfish.acequia.io/guerin/.agents/182bd1a7-a376-4dd0-b445-578adc6635b9/2026-06-18/notes/00-step-2026Sandy_v2.md) · session 2026-06-18 · discussion: Talk: Fire Progression
**Date:** 2026-06-18. **Trigger:** dock request from `31f69717` (add 2026Sandy_v2 to the SandyFire STAC) + the standing open action in `bead-bind-startup.md` (recompute TOA from the true ignition origin).
## What ran `2026-06-18/skills/progression-maker.mjs` — the bead's first executable (the spec in `notes/00` made code): - **Inputs:** 6 ordered perimeters (GeoJSON MultiPolygon) from `cbf8b027`'s `2026SandyFire/perimeters/` (18:02Z/183ac → 2026-05-20T23:13Z/2114.51ac) + ignition origin `34.25235,-118.746484` @ **17:17 Z**. - **Method:** scanline rasterize each perimeter → inside mask; chamfer (0.95509/1.36930) distance-to-boundary, signed by mask → φ; per-interval level-set blend `f = near/(near−far)`, earliest-first (monotone front); the **origin→P0** interval uses pixel-distance-from-origin as the near front so minute-0 sits at the true ignition, not at P0. Minutes-from-origin RGB-packed (R high), alpha = burned. - **Output:** `artifacts/2026Sandy_v2/2026Sandy_v2.{png,pgw,json}` — 1122×651 @ 0.00005° (~5 m), 341,197 burned px. worldfile `0.00005,0,0,-0.00005,-118.76951464884718,34.25297558`.
## Resolves the t0 discrepancy (notes/01) v1 minute-0 = 23:49 Z (centroid origin); v2 minute-0 = **17:17 Z at the reported ignition point** (north of v1's bbox top), with the early AEVEX heat perimeters (18:02/22:09 Z) folded ahead of the NIFC set so the gradient reaches back to ignition.
## Flux - STAC item `toa-2026Sandy_v2` minted in `cbf8b027` `2026SandyFire-progression` (+ collection item link; temporal start widened to 17:17 Z; bbox widened north). `toa:source` marks it as superseding v1. - Replied to requester dock `31f69717/uploads/`.
## Open / caveats - Dep-free re-impl, **not** the Simtable progressionMaker — v2-draft. Chamfer ≈ Euclidean; cell coarser than v1 (~5 m vs ~2.8 m). Re-run finer with `--cell`. - Assets are bead-local — **needs `/bead-sync`** of `182bd1a7` (+ `cbf8b027` for the item) before the STAC hrefs resolve. - Not yet wired into the incident-viewer progression renderer.