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https://github.com/acaloiaro/roam-location
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Detect twilight by checking when the solar radiation sensor reads low but positive values (< 30 W/m²) while the sun is geometrically near the horizon (sinusoidal fraction < 0.2 or outside model daylight hours). Morning/afternoon local time distinguishes dawn from dusk without hard-coding sunrise/sunset times.
100 lines
3.1 KiB
Go
100 lines
3.1 KiB
Go
package weather
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import "math"
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// Condition is an inferred weather condition with a human label and emoji.
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type Condition struct {
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Label string `json:"label"`
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Emoji string `json:"emoji"`
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}
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// peakSolarRadiation is the approximate clear-sky maximum at sea level (W/m²).
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const peakSolarRadiation = 950.0
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// twilightSolar is the solar radiation threshold (W/m²) below which the sun is considered
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// low in the sky, producing dawn or dusk conditions.
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const twilightSolar = 30.0
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// sunFraction returns the fraction of peak solar radiation expected at the given
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// local time of day, using a simple sinusoidal model (sunrise ~6, sunset ~18).
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// Returns 0 outside of daylight hours.
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func sunFraction(localMinutes int) float64 {
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localMinutes = ((localMinutes % 1440) + 1440) % 1440
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localHourF := float64(localMinutes) / 60.0
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if localHourF < 6 || localHourF >= 18 {
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return 0
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}
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return math.Sin(math.Pi * (localHourF - 6) / 12.0)
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}
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// Infer derives a weather condition from sensor readings and approximate location.
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// Solar radiation is normalized against the expected clear-sky maximum for the
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// current time of day, so conditions are accurate at any hour.
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func Infer(d Data, lat, lon float64) *Condition {
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solar := 0.0
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if d.SolarRadiation != nil {
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solar = *d.SolarRadiation
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}
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humidity := 0.0
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if d.Humidity != nil {
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humidity = *d.Humidity
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}
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// Rain takes priority.
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if d.HourlyRainIn != nil && *d.HourlyRainIn > 0.02 {
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if *d.HourlyRainIn > 0.1 {
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return &Condition{"Heavy rain", "⛈️"}
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}
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return &Condition{"Rainy", "🌧️"}
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}
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// Near-rain: very high humidity and overcast.
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if humidity >= 95 && solar < 10 {
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return &Condition{"Foggy", "🌫️"}
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}
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// Estimate local time from longitude (rough UTC offset).
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utcMinutes := d.LastUpdated.Hour()*60 + d.LastUpdated.Minute()
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localMinutes := utcMinutes + int(math.Round(lon/15))*60
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localMinutes = ((localMinutes % 1440) + 1440) % 1440
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fraction := sunFraction(localMinutes)
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isDaytime := fraction > 0
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isMorning := localMinutes < 720
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// Dawn/dusk: sensor detects low but positive solar radiation while the sun is
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// geometrically near the horizon (fraction < 0.2 or before/after model daylight).
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// isMorning distinguishes the two without hard-coding sunrise/sunset hours.
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if solar > 0 && solar < twilightSolar && (!isDaytime || fraction < 0.2) {
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if isMorning {
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return &Condition{"Dawn", "🌅"}
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}
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return &Condition{"Dusk", "🌇"}
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}
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if !isDaytime || solar < 10 {
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if !isDaytime {
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if humidity > 80 {
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return &Condition{"Cloudy night", "☁️"}
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}
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return &Condition{"Clear night", "🌙"}
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}
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// Daytime with no solar — heavy overcast or dense cloud.
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return &Condition{"Overcast", "☁️"}
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}
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// Normalize solar radiation against the expected clear-sky max for this hour.
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// Clamp to [0, 1] to absorb sensor noise.
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normalized := math.Min(solar/(peakSolarRadiation*fraction), 1.0)
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if normalized > 0.85 {
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return &Condition{"Sunny", "🌞"}
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}
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if normalized > 0.55 {
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return &Condition{"Partly cloudy", "⛅"}
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}
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if normalized > 0.15 {
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return &Condition{"Mostly cloudy", "🌥️"}
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}
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return &Condition{"Overcast", "☁️"}
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}
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