feat: Support Gaussian grids like O1280 for IFS HRES

Author: patrick-zippenfenig

examples/temperature.html

@@ -46,7 +46,7 @@
 			});
 
 			// s3 storage structure: /data_spatial/{domain}/{modelRun /year/month/day/time}Z/{selectedTime year-month-day-time.om}?variable={variable}
-			const omUrl = `https://map-tiles.open-meteo.com/data_spatial/dwd_icon/2025/10/15/1200Z/2025-10-15T1400.om?variable=temperature_2m`;
+			const omUrl = `https://map-tiles.open-meteo.com/data_spatial/ecmwf_ifs/2025/10/20/0000Z/2025-10-20T1200.om?variable=temperature_2m`;
 
 			map.on('load', () => {
 				map.addSource('omFileSource', {

src/utils/domains.ts

@@ -377,6 +377,27 @@ export const domainOptions: Array<Domain> = [
 		model_interval: 6,
 		windUVComponents: true
 	},
+		{
+		value: 'ecmwf_ifs',
+		label: 'ECMWF IFS HRES',
+		grid: {
+			nx: 1440, // 6599680
+			ny: 721,
+			latMin: -90,
+			lonMin: -180,
+			dx: 360 / 1440,
+			dy: 180 / (721 - 1),
+			zoom: 3.2,
+			gaussianGridLatitudeLines: 1280,
+			center: function () {
+				this.center = getCenterPoint(this);
+				return this;
+			}
+		},
+		time_interval: 1,
+		model_interval: 3,
+		windUVComponents: true
+	},
 
 	// GEM
 	{

src/worker.ts

@@ -172,16 +172,60 @@ self.onmessage = async (message) => {
 				const ind = j + i * TILE_SIZE;
 				const lon = tile2lon(x + j / TILE_SIZE, z);
 
-				const { index, xFraction, yFraction } = getIndexAndFractions(
-					lat,
-					lon,
-					domain,
-					projectionGrid,
-					ranges,
-					[latMin, lonMin, latMax, lonMax]
-				);
-
-				let px = interpolator(values as Float32Array, index, xFraction, yFraction, ranges);
+				let px = NaN
+				if (domain.grid.gaussianGridLatitudeLines) {
+					const latitudeLines = domain.grid.gaussianGridLatitudeLines
+					const dy = 180 / (2 * latitudeLines + 0.5);
+					const count = 6599680;
+
+					const nearestNeighbor = false
+					if (nearestNeighbor) {
+						// nearest neighbor
+						const y = (Math.round(latitudeLines - 1 - (lat - dy / 2) / dy) + 2 * latitudeLines) % (2 * latitudeLines);
+						const nx = y < latitudeLines ? 20 + y * 4 : (2 * latitudeLines - y - 1) * 4 + 20;
+						const dx = 360 / nx;
+						const x = (Math.floor(lon / dx) + nx) % nx;
+						const integral = y < latitudeLines ? 2 * y * y + 18 * y : count - (2 * (2 * latitudeLines - y) * (2 * latitudeLines - y) + 18 * (2 * latitudeLines - y));
+						const index = integral + x
+						px = values[index]
+					} else {
+						// linear interpolation
+						const yLower = (Math.floor(latitudeLines - 1 - (lat - dy / 2) / dy) + 2 * latitudeLines) % (2 * latitudeLines);
+						const yFraction = (latitudeLines - 1 - (lat - dy / 2) / dy) % 1
+						const yUpper = yLower + 1;
+						const nxLower = yLower < latitudeLines ? 20 + yLower * 4 : (2 * latitudeLines - yLower - 1) * 4 + 20;
+						const nxUpper = yUpper < latitudeLines ? 20 + yUpper * 4 : (2 * latitudeLines - yUpper - 1) * 4 + 20;
+						const dxLower = 360 / nxLower;
+						const dxUpper = 360 / nxUpper;
+						const xLower0 = (Math.floor(lon / dxLower) + nxLower) % nxLower;
+						const xUpper0 = (Math.floor(lon / dxUpper) + nxUpper) % nxUpper;
+						const integralLower = yLower < latitudeLines ? 2 * yLower * yLower + 18 * yLower : count - (2 * (2 * latitudeLines - yLower) * (2 * latitudeLines - yLower) + 18 * (2 * latitudeLines - yLower));
+						const integralUpper = yUpper < latitudeLines ? 2 * yUpper * yUpper + 18 * yUpper : count - (2 * (2 * latitudeLines - yUpper) * (2 * latitudeLines - yUpper) + 18 * (2 * latitudeLines - yUpper));
+						const indexLower = integralLower + xLower0;
+						const indexUpper = integralUpper + xUpper0;
+						const xFractionLower = (lon / dxLower) % 1
+						const xFractionUpper = (lon / dxUpper) % 1
+						const p0 = values[indexLower]
+						const p1 = values[indexLower+1]
+						const p2 = values[indexUpper]
+						const p3 = values[indexUpper+1]
+						px = p0 * (1 - xFractionLower) * (1 - yFraction) +
+							p1 * xFractionLower * (1 - yFraction) +
+							p2 * (1 - xFractionUpper) * yFraction +
+							p3 * xFractionUpper * yFraction
+					}
+				} else {
+					const { index, xFraction, yFraction } = getIndexAndFractions(
+						lat,
+						lon,
+						domain,
+						projectionGrid,
+						ranges,
+						[latMin, lonMin, latMax, lonMax]
+					);
+
+					px = interpolator(values as Float32Array, index, xFraction, yFraction, ranges);
+				}
 
 				if (hideZero.includes(variable.value)) {
 					if (px < 0.25) {