step one

internal/weather/gfs/constants.go

@@ -0,0 +1,141 @@
+package gfs
+
+import "fmt"
+
+// Dataset shape: (hour, pressure_level, variable, latitude, longitude).
+// Matches the cube layout used by the reference Tawhiri implementation.
+const (
+	NumHours      = 65  // 0, 3, 6, ..., 192 hours forecast
+	NumLevels     = 47  // pressure levels
+	NumVariables  = 3   // geopotential height, U-wind, V-wind
+	NumLatitudes  = 361 // -90.0 to +90.0 inclusive in 0.5° steps
+	NumLongitudes = 720 // 0.0 to 359.5 in 0.5° steps
+
+	HourStep   = 3
+	MaxHour    = 192
+	Resolution = 0.5
+	LatStart   = -90.0
+	LonStart   = 0.0
+
+	VarHeight = 0
+	VarWindU  = 1
+	VarWindV  = 2
+
+	ElementSize = 4 // float32
+
+	// DatasetSize is the canonical file size: every grid cell × element size.
+	DatasetSize int64 = int64(NumHours) * int64(NumLevels) * int64(NumVariables) *
+		int64(NumLatitudes) * int64(NumLongitudes) * int64(ElementSize)
+)
+
+// LevelSet identifies which GRIB file (primary/secondary) carries a level.
+type LevelSet int
+
+const (
+	LevelSetA LevelSet = iota // pgrb2 — primary file
+	LevelSetB                 // pgrb2b — secondary file
+)
+
+// Pressures lists the 47 pressure levels (hPa) in dataset index order,
+// descending from surface to top of atmosphere.
+var Pressures = [NumLevels]int{
+	1000, 975, 950, 925, 900, 875, 850, 825, 800, 775,
+	750, 725, 700, 675, 650, 625, 600, 575, 550, 525,
+	500, 475, 450, 425, 400, 375, 350, 325, 300, 275,
+	250, 225, 200, 175, 150, 125, 100, 70, 50, 30,
+	20, 10, 7, 5, 3, 2, 1,
+}
+
+// PressuresPgrb2 lists the levels carried by the primary GRIB file.
+var PressuresPgrb2 = []int{
+	10, 20, 30, 50, 70, 100, 150, 200, 250, 300, 350, 400,
+	450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 925,
+	950, 975, 1000,
+}
+
+// PressuresPgrb2b lists the levels carried by the secondary GRIB file.
+var PressuresPgrb2b = []int{
+	1, 2, 3, 5, 7, 125, 175, 225, 275, 325, 375, 425,
+	475, 525, 575, 625, 675, 725, 775, 825, 875,
+}
+
+var pressureIndex map[int]int
+var pressureLevelSet map[int]LevelSet
+
+func init() {
+	pressureIndex = make(map[int]int, NumLevels)
+	for i, p := range Pressures {
+		pressureIndex[p] = i
+	}
+	pressureLevelSet = make(map[int]LevelSet, NumLevels)
+	for _, p := range PressuresPgrb2 {
+		pressureLevelSet[p] = LevelSetA
+	}
+	for _, p := range PressuresPgrb2b {
+		pressureLevelSet[p] = LevelSetB
+	}
+}
+
+// PressureIndex returns the dataset index for a pressure level in hPa,
+// or -1 when the level is unknown.
+func PressureIndex(hPa int) int {
+	idx, ok := pressureIndex[hPa]
+	if !ok {
+		return -1
+	}
+	return idx
+}
+
+// PressureLevelSet returns the GRIB file set carrying a pressure level.
+func PressureLevelSet(hPa int) (LevelSet, bool) {
+	ls, ok := pressureLevelSet[hPa]
+	return ls, ok
+}
+
+// HourIndex returns the dataset time index for a forecast hour, or -1 when
+// the hour is outside the range or not a multiple of HourStep.
+func HourIndex(hour int) int {
+	if hour < 0 || hour > MaxHour || hour%HourStep != 0 {
+		return -1
+	}
+	return hour / HourStep
+}
+
+// Hours returns the full list of forecast hours, [0, 3, 6, ..., MaxHour].
+func Hours() []int {
+	out := make([]int, 0, NumHours)
+	for h := 0; h <= MaxHour; h += HourStep {
+		out = append(out, h)
+	}
+	return out
+}
+
+// VariableIndex maps a GRIB (category, number) pair to a dataset variable
+// index, returning -1 for parameters this dataset does not store.
+func VariableIndex(parameterCategory, parameterNumber int) int {
+	switch {
+	case parameterCategory == 3 && parameterNumber == 5:
+		return VarHeight
+	case parameterCategory == 2 && parameterNumber == 2:
+		return VarWindU
+	case parameterCategory == 2 && parameterNumber == 3:
+		return VarWindV
+	default:
+		return -1
+	}
+}
+
+// S3 URL configuration for NOAA GFS data on the public S3 mirror.
+const S3BaseURL = "https://noaa-gfs-bdp-pds.s3.amazonaws.com"
+
+// GribURL returns the S3 URL for a primary (pgrb2) GRIB file.
+func GribURL(date string, runHour, forecastStep int) string {
+	return fmt.Sprintf("%s/gfs.%s/%02d/atmos/gfs.t%02dz.pgrb2.0p50.f%03d",
+		S3BaseURL, date, runHour, runHour, forecastStep)
+}
+
+// GribURLB returns the S3 URL for a secondary (pgrb2b) GRIB file.
+func GribURLB(date string, runHour, forecastStep int) string {
+	return fmt.Sprintf("%s/gfs.%s/%02d/atmos/gfs.t%02dz.pgrb2b.0p50.f%03d",
+		S3BaseURL, date, runHour, runHour, forecastStep)
+}

internal/weather/gfs/file.go

@@ -0,0 +1,150 @@
+package gfs
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+	"os"
+	"time"
+
+	mmap "github.com/edsrzf/mmap-go"
+)
+
+// File is an mmap-backed wind dataset file. The layout is a flat C-order
+// row-major array of float32 values, shape (hour, level, variable, lat, lng).
+type File struct {
+	mm       mmap.MMap
+	file     *os.File
+	writable bool
+	// Epoch is the forecast run time (UTC) the file represents.
+	Epoch time.Time
+}
+
+// Open opens an existing dataset file for reading.
+func Open(path string, epoch time.Time) (*File, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("open dataset: %w", err)
+	}
+	info, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, fmt.Errorf("stat dataset: %w", err)
+	}
+	if info.Size() != DatasetSize {
+		f.Close()
+		return nil, fmt.Errorf("dataset should be %d bytes (was %d)", DatasetSize, info.Size())
+	}
+	mm, err := mmap.Map(f, mmap.RDONLY, 0)
+	if err != nil {
+		f.Close()
+		return nil, fmt.Errorf("mmap dataset: %w", err)
+	}
+	return &File{mm: mm, file: f, writable: false, Epoch: epoch}, nil
+}
+
+// Create creates a new dataset file of the canonical size, mmap'd read-write.
+func Create(path string) (*File, error) {
+	f, err := os.Create(path)
+	if err != nil {
+		return nil, fmt.Errorf("create dataset: %w", err)
+	}
+	if err := f.Truncate(DatasetSize); err != nil {
+		f.Close()
+		return nil, fmt.Errorf("truncate dataset: %w", err)
+	}
+	mm, err := mmap.MapRegion(f, int(DatasetSize), mmap.RDWR, 0, 0)
+	if err != nil {
+		f.Close()
+		return nil, fmt.Errorf("mmap dataset: %w", err)
+	}
+	return &File{mm: mm, file: f, writable: true}, nil
+}
+
+// OpenWritable opens an existing dataset file for read-write access.
+// Used when resuming a partial download.
+func OpenWritable(path string) (*File, error) {
+	f, err := os.OpenFile(path, os.O_RDWR, 0o644)
+	if err != nil {
+		return nil, fmt.Errorf("open dataset rw: %w", err)
+	}
+	info, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, fmt.Errorf("stat dataset: %w", err)
+	}
+	if info.Size() != DatasetSize {
+		f.Close()
+		return nil, fmt.Errorf("dataset should be %d bytes (was %d)", DatasetSize, info.Size())
+	}
+	mm, err := mmap.MapRegion(f, int(DatasetSize), mmap.RDWR, 0, 0)
+	if err != nil {
+		f.Close()
+		return nil, fmt.Errorf("mmap dataset: %w", err)
+	}
+	return &File{mm: mm, file: f, writable: true}, nil
+}
+
+// offset returns the byte offset of the [hour][level][variable][lat][lng] cell.
+func offset(hour, level, variable, lat, lng int) int64 {
+	idx := int64(hour)
+	idx = idx*int64(NumLevels) + int64(level)
+	idx = idx*int64(NumVariables) + int64(variable)
+	idx = idx*int64(NumLatitudes) + int64(lat)
+	idx = idx*int64(NumLongitudes) + int64(lng)
+	return idx * int64(ElementSize)
+}
+
+// Val reads one cell as a float32.
+func (d *File) Val(hour, level, variable, lat, lng int) float32 {
+	off := offset(hour, level, variable, lat, lng)
+	return math.Float32frombits(binary.LittleEndian.Uint32(d.mm[off : off+4]))
+}
+
+// SetVal writes one cell. Only valid on writable files.
+func (d *File) SetVal(hour, level, variable, lat, lng int, val float32) {
+	off := offset(hour, level, variable, lat, lng)
+	binary.LittleEndian.PutUint32(d.mm[off:off+4], math.Float32bits(val))
+}
+
+// BlitGribData copies one decoded GRIB grid into the dataset, flipping the
+// latitude axis from GRIB's north-to-south scan order to our south-to-north
+// storage order. gribData must be 361*720 = 259920 float64 values.
+func (d *File) BlitGribData(hourIdx, levelIdx, varIdx int, gribData []float64) error {
+	expected := NumLatitudes * NumLongitudes
+	if len(gribData) != expected {
+		return fmt.Errorf("grib data has %d values, expected %d", len(gribData), expected)
+	}
+	for lat := range NumLatitudes {
+		for lng := range NumLongitudes {
+			gribIdx := (360-lat)*NumLongitudes + lng
+			d.SetVal(hourIdx, levelIdx, varIdx, lat, lng, float32(gribData[gribIdx]))
+		}
+	}
+	return nil
+}
+
+// Flush flushes the mmap to disk.
+func (d *File) Flush() error {
+	if d.mm != nil {
+		return d.mm.Flush()
+	}
+	return nil
+}
+
+// Close unmaps and closes the file.
+func (d *File) Close() error {
+	if d.mm != nil {
+		if err := d.mm.Unmap(); err != nil {
+			d.file.Close()
+			return fmt.Errorf("unmap: %w", err)
+		}
+		d.mm = nil
+	}
+	if d.file != nil {
+		err := d.file.Close()
+		d.file = nil
+		return err
+	}
+	return nil
+}

internal/weather/gfs/wind.go

@@ -0,0 +1,109 @@
+package gfs
+
+import (
+	"time"
+
+	"predictor-refactored/internal/numerics"
+	"predictor-refactored/internal/weather"
+)
+
+// Wind is a WindField backed by a GFS dataset file.
+type Wind struct {
+	file *File
+}
+
+// NewWind returns a Wind backed by file.
+func NewWind(file *File) *Wind {
+	return &Wind{file: file}
+}
+
+// Epoch returns the forecast run time of the underlying file.
+func (w *Wind) Epoch() time.Time { return w.file.Epoch }
+
+// Source returns the source identifier "noaa-gfs-0p50".
+func (w *Wind) Source() string { return "noaa-gfs-0p50" }
+
+// Close releases the underlying file's resources.
+func (w *Wind) Close() error { return w.file.Close() }
+
+// Grid axes for the GFS 0.5-degree dataset.
+var (
+	hourAxis = numerics.Axis{
+		Left: 0,
+		Step: float64(HourStep),
+		N:    NumHours,
+		Name: "hour",
+	}
+	latAxis = numerics.Axis{
+		Left: LatStart,
+		Step: Resolution,
+		N:    NumLatitudes,
+		Name: "lat",
+	}
+	lngAxis = numerics.Axis{
+		Left: LonStart,
+		Step: Resolution,
+		N:    NumLongitudes,
+		Wrap: true,
+		Name: "lng",
+	}
+)
+
+// Wind samples the field at the given UNIX time, geographic coordinate, and
+// altitude. Vertical interpolation matches Tawhiri: locate the two pressure
+// levels whose interpolated geopotential heights bracket alt, then linearly
+// interpolate U and V between them.
+func (w *Wind) Wind(t, lat, lng, alt float64) (weather.Sample, error) {
+	hours := (t - float64(w.file.Epoch.Unix())) / 3600.0
+
+	bh, err := hourAxis.Locate(hours)
+	if err != nil {
+		return weather.Sample{}, err
+	}
+	bla, err := latAxis.Locate(lat)
+	if err != nil {
+		return weather.Sample{}, err
+	}
+	bln, err := lngAxis.Locate(lng)
+	if err != nil {
+		return weather.Sample{}, err
+	}
+	bs := [3]numerics.Bracket{bh, bla, bln}
+
+	height := func(level int) func(i, j, k int) float64 {
+		return func(i, j, k int) float64 {
+			return float64(w.file.Val(i, level, VarHeight, j, k))
+		}
+	}
+
+	levelIdx := numerics.Bisect(0, NumLevels-2, alt, func(level int) float64 {
+		return numerics.EvalTrilinear(bs, height(level))
+	})
+
+	lowerHGT := numerics.EvalTrilinear(bs, height(levelIdx))
+	upperHGT := numerics.EvalTrilinear(bs, height(levelIdx+1))
+
+	var altFrac float64
+	if lowerHGT != upperHGT {
+		altFrac = (upperHGT - alt) / (upperHGT - lowerHGT)
+	} else {
+		altFrac = 0.5
+	}
+
+	component := func(level, variable int) float64 {
+		return numerics.EvalTrilinear(bs, func(i, j, k int) float64 {
+			return float64(w.file.Val(i, level, variable, j, k))
+		})
+	}
+
+	lowerU := component(levelIdx, VarWindU)
+	upperU := component(levelIdx+1, VarWindU)
+	lowerV := component(levelIdx, VarWindV)
+	upperV := component(levelIdx+1, VarWindV)
+
+	return weather.Sample{
+		U:          lowerU*altFrac + upperU*(1-altFrac),
+		V:          lowerV*altFrac + upperV*(1-altFrac),
+		AboveModel: altFrac < 0,
+	}, nil
+}