developmentseed
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+# NLDAS icechunk example — Design
+
+- **Date:** 2026-05-27
+- **Issues:** [#569](https://github.com/developmentseed/deck.gl-raster/issues/569)
+- **Status:** Proposed
+- **Related:** [`2026-04-17-ecmwf-zarr-animation-design.md`](2026-04-17-ecmwf-zarr-animation-design.md) — the closest precedent example; this design deliberately strips its UI down to a static frame
+
+## Problem
+
+We want an example proving that an [icechunk](https://icechunk.io) repository can
+be read in the browser and rendered with `deck.gl-raster`, using
+[`icechunk-js`](https://github.com/EarthyScience/icechunk-js) as a
+zarrita-compatible store. icechunk is increasingly used to publish analysis-ready
+and *virtual* Zarr (chunks that reference byte ranges inside other cloud objects),
+and we currently have no example demonstrating that path.
+
+The target dataset, suggested in the issue, is
+[NLDAS-3](https://github.com/virtual-zarr/nldas-icechunk) — NASA's North American
+Land Data Assimilation System v3 daily forcing data, virtualized into an icechunk
+repo:
+
+- **Repo:** `https://nasa-waterinsight.s3.us-west-2.amazonaws.com/virtual-zarr-store/NLDAS-3-icechunk`
+- **Access:** public / anonymous.
+- **Virtual chunks:** reference the original NLDAS-3 files under
+  `s3://nasa-waterinsight/NLDAS3/forcing/daily/` — **the same bucket**.
+
+Feasibility facts verified during design:
+
+- The entire `nasa-waterinsight` bucket returns `Access-Control-Allow-Origin: *`
+  for `GET`/`HEAD`, so both the icechunk repo metadata and the virtual source
+  objects are reachable from a browser origin.
+- `icechunk-js@0.4.0` declares `zarrita ^0.5 || ^0.6 || ^0.7` as a peer
+  dependency, matching this repo's `zarrita@0.7.3`.
+- The repo's `config.yaml` declares exactly one virtual chunk container:
+  ```yaml
+  virtual_chunk_containers:
+    s3://nasa-waterinsight/NLDAS3/forcing/daily/:
+      url_prefix: s3://nasa-waterinsight/NLDAS3/forcing/daily/
+      store: !s3 { region: us-west-2, anonymous: false, ... }
+  ```
+  The container's underlying objects are nonetheless publicly readable over
+  HTTPS (verified), so the browser can fetch them unsigned despite
+  `anonymous: false` in the stored config.
+
+The working Python recipe (provided by @kylebarron) confirms what the browser
+code must replicate:
+
+```python
+storage = icechunk.s3_storage(bucket='nasa-waterinsight',
+    prefix="virtual-zarr-store/NLDAS-3-icechunk", region="us-west-2", anonymous=True)
+virtual_credentials = icechunk.containers_credentials({
+    "s3://nasa-waterinsight/NLDAS3/forcing/daily/": icechunk.s3_anonymous_credentials()})
+repo = icechunk.Repository.open(storage=storage,
+    authorize_virtual_chunk_access=virtual_credentials)
+session = repo.readonly_session('main')
+ds = xr.open_zarr(session.store, consolidated=False, zarr_version=3, chunks={})
+```
+
+Two requirements fall out of this: **region** `us-west-2` (in the browser this is
+just encoded in the HTTPS host — `icechunk-js` has no region param), and
+**explicit authorization of the virtual chunk container** before chunk reads
+work.
+
+## Goals
+
+- A new `examples/nldas-icechunk` that renders a single Tair (air temperature)
+  timestep over North America with a temperature colormap.
+- Exercise the real integration seam: `IcechunkStore` → `zarrita.open` →
+  `ZarrLayer` (the existing `@developmentseed/deck.gl-zarr` layer).
+- Reuse this repo's idiomatic GPU colormap pipeline (rescale + colormap on the
+  GPU via `deck.gl-raster`'s gpu-modules), as in the ECMWF example.
+- `pnpm typecheck` passes and `pnpm dev` shows the rendered frame.
+
+## Non-goals
+
+- **No animation and no UI controls.** This is a minimal "plumbing" demo — one
+  pinned timestep, a fixed colormap, and a fixed rescale range. A time slider and
+  colormap/rescale controls are obvious follow-ups but explicitly out of scope.
+- **No GeoZarr support work.** The NLDAS virtual store is not GeoZarr-compliant;
+  we hard-code synthetic spatial attrs (the established ECMWF approach) rather
+  than teaching anything to parse NLDAS's native layout.
+- **No icechunk version-control UI** (snapshots/tags/branches). The example
+  checks out the default `main` branch only.
+
+## Design
+
+### Directory layout
+
+Mirrors `examples/dynamical-zarr-ecmwf`, minus the control-panel UI:
+
+```
+examples/nldas-icechunk/
+  index.html
+  package.json
+  tsconfig.json
+  vite.config.ts
+  README.md
+  src/
+    main.tsx            React entry
+    App.tsx             open store -> open Tair -> build ZarrLayer -> map + overlay
+    nldas/
+      metadata.ts       REPO_URL, VARIABLE, TIME_INDEX, rescale range,
+                        colormap choice, hard-coded NLDAS_GEOZARR_ATTRS
+      get-tile-data.ts  zarr.get(arr, sliceSpec) -> Float32 tile {data,width,height,byteLength}
+      render-tile.ts    GPU rescale + colormap pipeline (trimmed ECMWF render-tile)
+```
+
+No Chakra UI — there are no controls. Dependencies: `icechunk-js@^0.4.0`,
+`zarrita`, the workspace deck.gl-raster / deck.gl-zarr packages, the deck.gl
+peer packages, `maplibre-gl`, `react-map-gl`, and the shared
+`deck.gl-raster-examples-shared` (`DeckGlOverlay`).
+
+### Data flow
+
+1. **Open (once, on mount).** Build the store with the virtual chunk container
+   authorized. The `virtualChunkContainers` option lives on `ReadSession.open`
+   (not on `IcechunkStore.open(url, …)`), so we construct the session explicitly
+   and wrap it:
+   ```ts
+   const storage = new HttpStorage(REPO_URL); // region encoded in the HTTPS host
+   // VCC name (from config.yaml) -> public HTTPS prefix for the source objects
+   const virtualChunkContainers = new Map([[
+     "s3://nasa-waterinsight/NLDAS3/forcing/daily/",
+     "https://nasa-waterinsight.s3.us-west-2.amazonaws.com/NLDAS3/forcing/daily/",
+   ]]);
+   // exact entry point (Repository.checkoutBranch vs ReadSession.open with an
+   // explicit snapshot id) is pinned at the smoke-test step below
+   const session = await /* main-branch read session */;
+   const store = await IcechunkStore.open(session); // withRangeCoalescing is fn-typed; omit
+   const arr = await zarr.open(store.resolve("/Tair"), { kind: "array" });
+   ```
+   Use `zarr.open.v3` if auto-detection misfires — icechunk is always Zarr v3.
+   Assert the dtype is float; throw with a clear message otherwise (ECMWF
+   precedent). No custom `FetchClient` is needed: the source objects are public,
+   so the default client's unsigned `fetch` succeeds.
+2. **Colormap.** Fetch the shipped `colormaps.png`, `decodeColormapSprite` to
+   `ImageData`, and `createColormapTexture` once the luma `Device` arrives via
+   the overlay's `onDeviceInitialized` callback. Identical to ECMWF.
+3. **Layer.** Construct
+   `ZarrLayer({ node: arr, metadata: NLDAS_GEOZARR_ATTRS, selection: { <timeDim>: TIME_INDEX }, getTileData, renderTile, maxRequests })`.
+   The layer tiles the single-level array; `getTileData` pulls one chunk per tile
+   via `zarr.get(arr, options.sliceSpec)`; `renderTile` applies the fixed rescale
+   + colormap on the GPU.
+4. **Map.** A `maplibre-gl` basemap centered on North America (≈ lon −98, lat 39,
+   zoom ≈ 3.5) with the shared `DeckGlOverlay` (interleaved).
+
+### Spatial metadata (the one non-obvious piece)
+
+NLDAS-3 virtual-zarr is not GeoZarr-compliant, so — exactly like ECMWF's
+`ECMWF_GEOZARR_ATTRS` — we hard-code a synthetic attrs object and pass it as
+`ZarrLayer`'s `metadata` prop:
+
+```ts
+{
+  "spatial:dimensions": [<yDim>, <xDim>],   // e.g. ["lat", "lon"]
+  "spatial:transform": [a, b, c, d, e, f],  // @developmentseed/affine convention
+  "spatial:shape": [height, width],
+  "proj:code": "EPSG:4326",
+}
+```
+
+The **exact grid values** (spatial dim names, the non-spatial time dim name,
+shape, origin, pixel size, and crucially the latitude **row direction**) are not
+guessed — they are read from the store once during implementation by logging
+`arr.shape` and reading the 1-D lat/lon coordinate arrays, then frozen into
+`metadata.ts` with a comment recording where they came from. Tair's units
+(likely Kelvin) are confirmed the same way and drive a fixed rescale range plus a
+temperature colormap choice.
+
+### Error handling
+
+- Async open effect uses a `cancelled` flag (ECMWF precedent) to avoid setting
+  state after unmount.
+- Non-float dtype throws with a descriptive message.
+- Layer is only constructed once both the opened array and the colormap texture
+  are ready.
+
+## Risks / smoke-test before building UI
+
+- **Virtual chunk resolution — the load-bearing risk.** Mechanism is understood
+  (the `virtualChunkContainers` map above), but two unknowns remain until run: the
+  exact session entry point that accepts `virtualChunkContainers`
+  (`Repository.checkoutBranch` vs `ReadSession.open` with an explicit snapshot id),
+  and whether the manifest stores chunk locations such that the container's
+  `url_prefix` matches and rewrites cleanly to the HTTPS prefix. **First
+  implementation step is a throwaway script/console call** that opens the store
+  and `zarr.get`s a single Tair chunk, confirming bytes return, *before* any
+  layer/UI work. If it fails, revisit the approach here rather than pressing on.
+- **Zarr version.** icechunk is Zarr v3 with no consolidated metadata; the store
+  serves metadata directly. Prefer `zarr.open.v3` if plain `open` mis-detects.
+
+## Testing
+
+Examples in this repo are demos without unit tests; verification is:
+
+- `pnpm typecheck` in the example.
+- Manual `pnpm dev` confirming Tair renders over North America with the colormap.
+
+A fresh worktree first needs submodule init + `pnpm install` + `pnpm build` so the
+workspace packages resolve.
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+# NLDAS-3 icechunk Example
+
+Renders a single timestep of NLDAS-3 near-surface air temperature from a public
+[icechunk](https://icechunk.io) repository, read in the browser via
+[`icechunk-js`](https://github.com/EarthyScience/icechunk-js) + zarrita and
+displayed with `@developmentseed/deck.gl-zarr`'s `ZarrLayer`.
+
+The store is a *virtual* Zarr: its chunks reference NLDAS-3 source objects in
+the same public `nasa-waterinsight` S3 bucket, authorized through a
+`virtualChunkContainers` map.
+
+## Setup
+
+1. Install dependencies from the repository root:
+   ```bash
+   pnpm install
+   ```
+2. Build the packages:
+   ```bash
+   pnpm build
+   ```
+3. Run the development server:
+   ```bash
+   cd examples/nldas-icechunk
+   pnpm dev
+   ```
+4. Open your browser to http://localhost:3000
+
+`src/nldas/metadata.ts` hard-codes the grid (origin, pixel size, shape, units,
+fill) because the virtual store is not GeoZarr-compliant.
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+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>NLDAS icechunk Example</title>
+    <style>
+      body {
+        margin: 0;
+        font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+      }
+      #root {
+        width: 100vw;
+        height: 100vh;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>
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+{
+  "name": "deck.gl-nldas-icechunk",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview",
+    "typecheck": "tsc --noEmit",
+    "publish": "pnpm build && gh-pages -d dist -b gh-pages -e examples/nldas-icechunk"
+  },
+  "dependencies": {
+    "@chakra-ui/react": "^3.34.0",
+    "@deck.gl/core": "^9.3.2",
+    "@deck.gl/geo-layers": "^9.3.2",
+    "@deck.gl/layers": "^9.3.2",
+    "@deck.gl/mapbox": "^9.3.2",
+    "@developmentseed/deck.gl-raster": "workspace:^",
+    "@developmentseed/deck.gl-zarr": "workspace:^",
+    "@emotion/react": "^11.14.0",
+    "@luma.gl/core": "^9.3.2",
+    "@luma.gl/shadertools": "^9.3.2",
+    "deck.gl-raster-examples-shared": "workspace:*",
+    "icechunk-js": "^0.4.0",
+    "maplibre-gl": "^5.24.0",
+    "react": "^19.2.5",
+    "react-dom": "^19.2.5",
+    "react-map-gl": "^8.1.1",
+    "zarrita": "^0.7.3"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^6.0.1",
+    "gh-pages": "^6.3.0",
+    "vite": "^8.0.0"
+  }
+}