From ca95e06ab731247ba6fa171d83b6d2f9b1e8e656 Mon Sep 17 00:00:00 2001
From: straitz <afanasiev.aysen@gmail.com>
Date: Tue, 16 Dec 2025 11:42:00 +0900
Subject: [PATCH] fixed wind data bug

---
 internal/pkg/grib/cube.go      | 2 +-
 internal/pkg/grib/extractor.go | 7 ++++---
 internal/pkg/grib/grib.go      | 2 +-
 internal/pkg/grib/util.go      | 8 ++++----
 4 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/internal/pkg/grib/cube.go b/internal/pkg/grib/cube.go
index d2015ec..64818dd 100644
--- a/internal/pkg/grib/cube.go
+++ b/internal/pkg/grib/cube.go
@@ -28,7 +28,7 @@ func openCube(path string) (*cube, error) {
 	}
 
 	const (
-		nT   = 97  // 0-96 hours with step 1 hour
+		nT   = 33  // 0-96 hours with step 3 hours (33 time steps)
 		nP   = 47  // 47 pressure levels matching tawhiri
 		nLat = 361
 		nLon = 720
diff --git a/internal/pkg/grib/extractor.go b/internal/pkg/grib/extractor.go
index 769b7cd..850a0e3 100644
--- a/internal/pkg/grib/extractor.go
+++ b/internal/pkg/grib/extractor.go
@@ -17,9 +17,10 @@ func (d *dataset) uv(lat, lon, alt float64, tHours float64) (float64, float64) {
 	x0 := int(math.Floor(ix)) % d.cube.lon
 	x1 := (x0 + 1) % d.cube.lon
 	wx := ix - float64(x0)
-	// For hourly data (step = 1 hour)
-	it0 := int(math.Floor(tHours))
-	wt := tHours - float64(it0)
+	// For 3-hourly data (step = 3 hours)
+	// Convert tHours to 3-hour index (e.g., 1.5 hours -> index 0.5, interpolate between 0 and 1)
+	it0 := int(math.Floor(tHours / 3.0))
+	wt := (tHours - float64(it0*3)) / 3.0 // Interpolation weight within 3-hour window
 	p := pressureFromAlt(alt)
 	ip0 := 0
 	for ip0+1 < len(pressureLevels) && pressureLevels[ip0+1] > p {
diff --git a/internal/pkg/grib/grib.go b/internal/pkg/grib/grib.go
index 32c4466..637a9aa 100644
--- a/internal/pkg/grib/grib.go
+++ b/internal/pkg/grib/grib.go
@@ -186,7 +186,7 @@ func (s *service) Update(ctx context.Context) error {
 }
 
 func assembleCube(dir string, run time.Time, cubePath string) error {
-	const sizePerVar = 97 * 47 * 361 * 720 * 4 // 97 time steps (0-96 hours), 47 pressure levels
+	const sizePerVar = 33 * 47 * 361 * 720 * 4 // 33 time steps (0-96 hours, 3-hour intervals), 47 pressure levels
 	total := int64(sizePerVar * 3)             // 3 variables: gh, u, v
 	f, err := os.Create(cubePath)
 	if err != nil {
diff --git a/internal/pkg/grib/util.go b/internal/pkg/grib/util.go
index 8de4af7..14b00be 100644
--- a/internal/pkg/grib/util.go
+++ b/internal/pkg/grib/util.go
@@ -6,11 +6,11 @@ import (
 	"time"
 )
 
-// Generate steps from 0 to 96 with step 1 hour (97 steps total)
-// GFS provides hourly data for 0-120 hours, we use first 96 hours
+// Generate steps from 0 to 96 with step 3 hours (33 steps total)
+// GFS provides 3-hourly data for 0-120 hours, we use first 96 hours (0, 3, 6, ..., 96)
 var steps = func() []int {
-	result := make([]int, 0, 97)
-	for i := 0; i <= 96; i++ {
+	result := make([]int, 0, 33)
+	for i := 0; i <= 96; i += 3 {
 		result = append(result, i)
 	}
 	return result