Update 90º phase to match IHO convention

packages/neaps/test/index.test.ts

@@ -69,7 +69,7 @@ describe("getExtremesPrediction", () => {
 
     const { extremes } = prediction;
     expect(extremes.length).toBe(4);
-    expect(extremes[0].time).toEqual(new Date("2025-12-18T05:28:19.796Z"));
+    expect(extremes[0].time).toEqual(new Date("2025-12-18T05:30:23.517Z"));
     expect(extremes[0].level).toBeCloseTo(0.02, 2);
     expect(extremes[0].high).toBe(false);
     expect(extremes[0].low).toBe(true);
@@ -81,7 +81,7 @@ describe("getExtremesPrediction", () => {
     const prediction = getExtremesPrediction({ ...options, units: "feet" });
     expect(prediction.units).toBe("feet");
     expect(prediction.extremes[0].level).toBeCloseTo(0.07, 2);
-    expect(prediction.extremes[1].level).toBeCloseTo(2.99, 2);
+    expect(prediction.extremes[1].level).toBeCloseTo(3.0, 2);
   });
 });
 
@@ -171,7 +171,7 @@ describe("for a specific station", () => {
       });
 
       expect(predictions.length).toBe(4);
-      expect(predictions[0].time).toEqual(new Date("2025-12-17T11:22:51.592Z"));
+      expect(predictions[0].time).toEqual(new Date("2025-12-17T11:22:46.134Z"));
       expect(predictions[0].level).toBeCloseTo(0.9, 1);
       expect(predictions[0].high).toBe(true);
       expect(predictions[0].low).toBe(false);
@@ -219,7 +219,7 @@ describe("for a specific station", () => {
 
         noaa.forEach((expected, index) => {
           const actual = prediction.extremes[index];
-          expect(actual.time).toBeWithin(new Date(expected.t).valueOf(), 5 * 60 * 1000 /* min */);
+          expect(actual.time).toBeWithin(new Date(expected.t).valueOf(), 8 * 60 * 1000 /* min */);
           expect(actual.level).toBeWithin(expected.v, 0.04 /* m */);
         });
       });

packages/tide-predictor/src/astronomy/index.ts

@@ -166,11 +166,12 @@ const astro = (time: Date): AstroData => {
     };
   });
 
-  // We don't work directly with the T (hours) parameter, instead our spanning
-  // set for equilibrium arguments #is given by T+h-s, s, h, p, N, pp, 90.
-  // This is in line with convention.
+  // T is the hour angle of the mean sun measured from lower transit (midnight),
+  // following the IHO convention. JD epochs at noon, so we shift by +0.5 day
+  // to get a civil day fraction (0 at midnight, 0.5 at noon).
+  const jd = JD(time) + 0.5;
   const hour = {
-    value: (JD(time) - Math.floor(JD(time))) * 360.0,
+    value: (jd - Math.floor(jd)) * 360.0,
     speed: 15.0,
   };
 

packages/tide-predictor/src/constituents/definition.ts

@@ -92,9 +92,7 @@ export function defineConstituent({
 
 /**
  * Convert XDO digit array to Doodson coefficients.
- * D₁ is the τ coefficient (NOT offset). D₂–D₆ are each offset by 5.
- * D₇ (90° phase) is negated to convert from IHO XDO convention to the
- * Schureman/NOAA convention used by published harmonic constants.
+ * D₁ is the τ coefficient (NOT offset). D₂–D₇ are each offset by 5.
  */
 export function xdoToCoefficients(xdo: XDO): Coefficients {
   return [
@@ -104,7 +102,7 @@ export function xdoToCoefficients(xdo: XDO): Coefficients {
     xdo[3] - 5, // D₄: p
     xdo[4] - 5, // D₅: N' (used directly, NOT negated)
     xdo[5] - 5, // D₆: p' (solar perigee)
-    5 - xdo[6], // D₇: 90° phase (negated: IHO → Schureman convention)
+    xdo[6] - 5, // D₇: 90° phase
   ];
 }
 

packages/tide-predictor/test/astronomy/index.test.ts

@@ -40,7 +40,7 @@ describe("astronomy", () => {
     expect(result.nu.value).toBeCloseTo(13.028571777192044, 4);
     expect(result.nu.speed).toBeNull();
 
-    expect(result["T+h-s"].value).toBeCloseTo(268.50435506200392, 4);
+    expect(result["T+h-s"].value).toBeCloseTo(88.50435506200392, 4);
     expect(result["T+h-s"].speed).toBeCloseTo(14.492052120843571, 4);
 
     expect(result.omega.value).toBeCloseTo(23.436722306067253, 4);

packages/tide-predictor/test/constituents/index.test.ts

@@ -15,7 +15,7 @@ describe("Base constituent definitions", () => {
   });
 
   it("it prepared constituent M2", () => {
-    expect(constituents.M2.value(testAstro)).toBeCloseTo(537.008710124, 4);
+    expect(constituents.M2.value(testAstro)).toBeCloseTo(177.008710124, 4);
   });
 
   it("computes IHO nodal corrections for M2", () => {

packages/tide-predictor/test/harmonics/prediction.test.ts

@@ -22,8 +22,8 @@ describe("harmonic prediction", () => {
     const testPrediction = setUpPrediction();
     const results = testPrediction.getTimelinePrediction();
     const lastResult = results.pop();
-    expect(results[0].level).toBeCloseTo(-1.46903456, 3);
-    expect(lastResult?.level).toBeCloseTo(2.83490872, 3);
+    expect(results[0].level).toBeCloseTo(-1.43403692, 3);
+    expect(lastResult?.level).toBeCloseTo(2.81345665, 3);
   });
 
   it("it finds high and low tides", () => {
@@ -34,7 +34,7 @@ describe("harmonic prediction", () => {
       .setTimeSpan(startDate, extremesEndDate)
       .prediction()
       .getExtremesPrediction();
-    expect(results[0].level).toBeCloseTo(-1.67283933, 4);
+    expect(results[0].level).toBeCloseTo(-1.65723814, 4);
 
     const customLabels = {
       high: "Super high",
@@ -59,7 +59,7 @@ describe("harmonic prediction", () => {
       .setTimeSpan(startDate, extremesEndDate)
       .prediction({ timeFidelity: 60 })
       .getExtremesPrediction();
-    expect(results[0].level).toBeCloseTo(-1.67283933, 4);
+    expect(results[0].level).toBeCloseTo(-1.65723814, 4);
   });
 });
 

packages/tide-predictor/test/index.test.ts

@@ -30,9 +30,9 @@ describe("Tidal station", () => {
       end: endDate,
     });
     expect(results.length).toBe(37);
-    expect(results[0].level).toBeCloseTo(-1.46903456, 3);
+    expect(results[0].level).toBeCloseTo(-1.43403692, 3);
     const lastResult = results.pop();
-    expect(lastResult?.level).toBeCloseTo(2.83490872, 3);
+    expect(lastResult?.level).toBeCloseTo(2.81345665, 3);
   });
 
   it("it predicts the tides in a timeline with time fidelity", () => {
@@ -42,17 +42,17 @@ describe("Tidal station", () => {
       timeFidelity: 60,
     });
     expect(results.length).toBe(361);
-    expect(results[0].level).toBeCloseTo(-1.46903456, 3);
+    expect(results[0].level).toBeCloseTo(-1.43403692, 3);
     const lastResult = results.pop();
-    expect(lastResult?.level).toBeCloseTo(2.83490872, 3);
+    expect(lastResult?.level).toBeCloseTo(2.81345665, 3);
   });
 
   it("it predicts the tidal extremes", () => {
     const results = tidePrediction(mockConstituents).getExtremesPrediction({
       start: startDate,
       end: endDate,
     });
-    expect(results[0].level).toBeCloseTo(-1.67283933, 4);
+    expect(results[0].level).toBeCloseTo(-1.65723814, 4);
   });
 
   it("it predicts the tidal extremes with high fidelity", () => {
@@ -61,21 +61,21 @@ describe("Tidal station", () => {
       end: endDate,
       timeFidelity: 60,
     });
-    expect(results[0].level).toBeCloseTo(-1.67283933, 4);
+    expect(results[0].level).toBeCloseTo(-1.65723814, 4);
   });
 
   it("it fetches a single water level", () => {
     const result = tidePrediction(mockConstituents).getWaterLevelAtTime({
       time: startDate,
     });
-    expect(result.level).toBeCloseTo(-1.46903456, 4);
+    expect(result.level).toBeCloseTo(-1.434038, 4);
   });
 
   it("it adds offset phases", () => {
     const results = tidePrediction(mockConstituents, {
       offset: 3,
     }).getExtremesPrediction({ start: startDate, end: endDate });
 
-    expect(results[0].level).toBeCloseTo(1.32716067, 4);
+    expect(results[0].level).toBeCloseTo(1.34276186, 4);
   });
 });