Store page: assume a GOES fixed grid when nothing names the satellite

js/store-page.js

@@ -56,7 +56,7 @@ const PRESETS = [
 // gridlook's keys (url, varname, projection, lat, lon, dimIndices_<dim>) and
 // this page's own, which gridlook ignores
 const defaults = { url: PRESETS[0].url, varname: "", projection: "mollweide", lat: null, lon: null,
-  t: 0, colour: "data", chunks: 1, cells: 1, coast: 1, grat: 1, pick: "", cam: null };
+  t: 0, colour: "data", chunks: 1, cells: 1, coast: 1, grat: 1, pick: "", cam: null, assume: "" };
 const state = { ...defaults, dims: {} };
 
 function readHash() {
@@ -74,6 +74,7 @@ function readHash() {
   const c = params.get("colour");
   if (["data", "area", "omega", "none"].includes(c)) state.colour = c;
   state.pick = params.get("pick") || "";
+  state.assume = R.ASSUME[params.get("assume")] ? params.get("assume") : "";
   const cam = (params.get("cam") || "").split(",").map(Number);
   state.cam = cam.length === 6 && cam.every(isFinite) ? cam : null;
   for (const [k, v] of params) if (k.startsWith("dimIndices_") && isFinite(+v)) state.dims[k.slice(11)] = Math.max(0, Math.round(+v));
@@ -90,6 +91,7 @@ function writeHash() {
     if (state.t) p.t = +state.t.toFixed(3);
     for (const k of ["colour", "chunks", "cells", "coast", "grat"]) if (state[k] !== defaults[k]) p[k] = state[k];
     if (state.pick) p.pick = state.pick;
+    if (state.assume) p.assume = state.assume;
     if (state.cam) p.cam = state.cam.map((x) => +x.toFixed(2)).join(",");
     history.replaceState(null, "", "#" + C.hashString(state.url, p));
     $("open-full").href = location.pathname + location.hash;
@@ -727,7 +729,10 @@ async function open() {
     if (!state.varname) throw new Error("the store lists no arrays: add ::varname=<array> to the address");
     if (![...sel.options].some((o) => o.value === state.varname)) { const o = document.createElement("option"); o.value = o.textContent = state.varname; sel.appendChild(o); }
     sel.value = state.varname;
-    const v = await R.describeVariable(s, state.varname);
+    const v = await R.describeVariable(s, state.varname, { assume: state.assume });
+    // the choice of satellite, offered only where the store leaves it open
+    $("assume-row").hidden = !(v.abiLike || (v.crs && v.crs.assumed));
+    $("assume").value = state.assume;
     const F = v.grid ? await crsOf(v) : null;
     if (serial !== openSerial) return;
     const g = v.grid || { x0: 0, dx: 1, y0: 0, dy: 1, nx: v.meta.shape[v.ix], ny: v.meta.shape[v.iy] };
@@ -1010,6 +1015,7 @@ $("centre-grid").addEventListener("click", () => {
   if (cur) { buildFlat(); place(); }
   writeHash();
 });
+$("assume").addEventListener("change", (e) => { state.assume = e.target.value; writeHash(); open(); });
 ui.colour.addEventListener("change", () => { state.colour = ui.colour.value; if (cur) { drawTexture(); showLegend(); } writeHash(); });
 for (const k of ["chunks", "cells", "coast", "grat"])
   $(k).addEventListener("change", () => { state[k] = $(k).checked ? 1 : 0; if (cur) { drawTexture(); place(); showLegend(); } writeHash(); });

js/store-read.js

@@ -193,7 +193,15 @@ async function bodyNamed(s, attrs, dir) {
 // Where the cells of the variable at path are, and in which CRS:
 // { path, meta, dims, ix, iy, grid (storecrs.gridOf), crs (a cfProj()-like
 // description or null), crsFrom, notes[] }.
-export async function describeVariable(s, path) {
+// Satellites whose fixed grid can be assumed when a store has GOES ABI scan
+// angles but names no satellite (the ABI fixed grid's own parameters).
+export const ASSUME = {
+  goes_east: { label: "GOES-East (75.0 W)", lon0: -75 },
+  goes_west: { label: "GOES-West (137.0 W)", lon0: -137 }
+};
+const ABI_H = 35786023;
+
+export async function describeVariable(s, path, opts = {}) {
   const meta = await nodeMeta(s, path);
   if (!meta || meta.group) throw new Error(`${path || "the root"} is not an array`);
   const nd = meta.shape.length;
@@ -275,19 +283,30 @@ export async function describeVariable(s, path) {
   }
 
   // without a transform, the coordinate arrays
-  let x = null, y = null, xs = 1, ys = 1, xc = null, yc = null;
+  let x = null, y = null, xs = 1, ys = 1, xc = null, yc = null, abiLike = false;
   if (!t && !curv) {
     const cx = coords[ix] ? await read1d(s, join(dir, dims[ix])) : null;
     const cy = coords[iy] ? await read1d(s, join(dir, dims[iy])) : null;
     if (cx && cy) {
       const lonlat = role[ix] === "lon" && role[iy] === "lat";
       x = axisOf(cx.values, { lon: lonlat || role[ix] === "rlon" });
       y = axisOf(cy.values);
+      // scan angles with no CRS: a GOES ABI fixed grid, if the user says whose
+      const u = String(cx.attrs.units || "").toLowerCase();
+      abiLike = !crs && !lonlat && x.regular && y.regular && (!u || u.startsWith("rad")) &&
+        Math.max(...[cx.values[0], cx.values[cx.values.length - 1], cy.values[0], cy.values[cy.values.length - 1]].map((q) => Math.abs(Number(q)))) <= 0.16;
+      if (abiLike && ASSUME[opts.assume]) {
+        const a = ASSUME[opts.assume];
+        crs = { proj4: `+proj=geos +h=${ABI_H} +lon_0=${a.lon0} +sweep=x +x_0=0 +y_0=0 +a=6378137 +b=6356752.31414 +units=m +no_defs`, name: `${a.label} fixed grid, assumed`, h: ABI_H, assumed: opts.assume };
+        crsFrom = `an assumption: the store names no CRS, and its x and y look like the GOES ABI fixed grid, here taken as ${a.label}`;
+      } else if (abiLike) notes.push("x and y look like GOES ABI scan angles (radians), but nothing names the satellite: choose one under Assume to place the grid");
       if (!lonlat && role[ix] !== "rlon") {
-        const h = crs && /\+proj=geos\b/.test(crs.def || crs.proj4 || "") && gma ? Number(gma.perspective_point_height) || 0 : 0;
+        const h = crs && crs.h ? crs.h : crs && /\+proj=geos\b/.test(crs.def || crs.proj4 || "") && gma ? Number(gma.perspective_point_height) || 0 : 0;
+        if (crs && crs.h && !cx.attrs.units) { xs = ys = h; } else {
         xs = unitScale(cx.attrs.units, h); ys = unitScale(cy.attrs.units, h);
+        }
       }
-      if (xs !== 1) notes.push(`x and y are in ${cx.attrs.units}: multiplied by ${xs} for the CRS, which is in metres`);
+      if (xs !== 1) notes.push(`x and y are in ${cx.attrs.units || "radians (assumed)"}: multiplied by ${xs} for the CRS, which is in metres`);
       // uneven but 1D (a Gaussian grid's latitudes, say): kept as they are
       if (!x.regular) xc = unwrapped(cx.values, lonlat || role[ix] === "rlon").map((v) => v * xs);
       if (!y.regular) yc = Array.from(cy.values, (v) => v * ys);
@@ -313,7 +332,7 @@ export async function describeVariable(s, path) {
   }
   if (!grid) notes.push("nothing in the store says where the cells are: drawn in index space");
   if (!crs && !curv) notes.push("no CRS found");
-  return { path, meta, dims, ix, iy, role, grid, crs, crsFrom, gm: gma, notes };
+  return { path, meta, dims, ix, iy, role, grid, crs, crsFrom, gm: gma, notes, abiLike };
 }
 
 // One chunk of the variable, as { data, shape } for the grid dimensions at

store.html

@@ -97,6 +97,14 @@ <h1>playproj</h1>
       <p id="describe" class="describe"></p>
       <table id="facts" class="readout"></table>
       <p id="notes" class="hint"></p>
+      <div id="assume-row" hidden>
+        <label class="row" for="assume"><span>Assume</span></label>
+        <select id="assume" class="wide" aria-label="Assume a satellite">
+          <option value="">Nothing: leave the grid unplaced</option>
+          <option value="goes_east">GOES-East fixed grid (75.0 W)</option>
+          <option value="goes_west">GOES-West fixed grid (137.0 W)</option>
+        </select>
+      </div>
     </section>
 
     <section>

test/check-storecrs.mjs

@@ -116,7 +116,12 @@ for (const t of man.stores) {
   let s, v;
   try {
     s = await R.openStore(`${base}/${t.name}`);
-    v = await R.describeVariable(s, t.variable);
+    if (t.assume) {
+      // left unplaced until a satellite is chosen
+      const v0 = await R.describeVariable(s, t.variable);
+      check(v0.abiLike && !v0.crs, `${t.name}: without an assumption, abiLike ${v0.abiLike}, crs ${JSON.stringify(v0.crs)}`);
+    }
+    v = await R.describeVariable(s, t.variable, { assume: t.assume });
   } catch (e) { check(false, `${t.name}: ${e.message}`); continue; }
   const g = v.grid;
   check(s.kind === (t.name.endsWith(".icechunk") ? "icechunk" : t.kind ? "zarr2" : "zarr3"), `${t.name}: opened as ${s.kind}`);

test/fixtures/store/abi.zarr/u_wind/zarr.json

@@ -0,0 +1,51 @@
+{
+  "shape": [
+    1,
+    60,
+    60
+  ],
+  "data_type": "float32",
+  "chunk_grid": {
+    "name": "regular",
+    "configuration": {
+      "chunk_shape": [
+        1,
+        30,
+        30
+      ]
+    }
+  },
+  "chunk_key_encoding": {
+    "name": "default",
+    "configuration": {
+      "separator": "/"
+    }
+  },
+  "fill_value": "NaN",
+  "codecs": [
+    {
+      "name": "bytes",
+      "configuration": {
+        "endian": "little"
+      }
+    },
+    {
+      "name": "zstd",
+      "configuration": {
+        "level": 0,
+        "checksum": false
+      }
+    }
+  ],
+  "attributes": {
+    "_FillValue": "AAAAAAAA+H8="
+  },
+  "dimension_names": [
+    "time",
+    "y",
+    "x"
+  ],
+  "zarr_format": 3,
+  "node_type": "array",
+  "storage_transformers": []
+}

test/fixtures/store/abi.zarr/x/zarr.json

@@ -0,0 +1,45 @@
+{
+  "shape": [
+    60
+  ],
+  "data_type": "float64",
+  "chunk_grid": {
+    "name": "regular",
+    "configuration": {
+      "chunk_shape": [
+        60
+      ]
+    }
+  },
+  "chunk_key_encoding": {
+    "name": "default",
+    "configuration": {
+      "separator": "/"
+    }
+  },
+  "fill_value": "NaN",
+  "codecs": [
+    {
+      "name": "bytes",
+      "configuration": {
+        "endian": "little"
+      }
+    },
+    {
+      "name": "zstd",
+      "configuration": {
+        "level": 0,
+        "checksum": false
+      }
+    }
+  ],
+  "attributes": {
+    "_FillValue": "AAAAAAAA+H8="
+  },
+  "dimension_names": [
+    "x"
+  ],
+  "zarr_format": 3,
+  "node_type": "array",
+  "storage_transformers": []
+}

test/fixtures/store/abi.zarr/y/zarr.json

@@ -0,0 +1,45 @@
+{
+  "shape": [
+    60
+  ],
+  "data_type": "float64",
+  "chunk_grid": {
+    "name": "regular",
+    "configuration": {
+      "chunk_shape": [
+        60
+      ]
+    }
+  },
+  "chunk_key_encoding": {
+    "name": "default",
+    "configuration": {
+      "separator": "/"
+    }
+  },
+  "fill_value": "NaN",
+  "codecs": [
+    {
+      "name": "bytes",
+      "configuration": {
+        "endian": "little"
+      }
+    },
+    {
+      "name": "zstd",
+      "configuration": {
+        "level": 0,
+        "checksum": false
+      }
+    }
+  ],
+  "attributes": {
+    "_FillValue": "AAAAAAAA+H8="
+  },
+  "dimension_names": [
+    "y"
+  ],
+  "zarr_format": 3,
+  "node_type": "array",
+  "storage_transformers": []
+}