ambient-local-exporter/pkg/weather/enrich.go

package weather

import (
	"math"
	"net/url"
	"strconv"

	"gitea.libretechconsulting.com/rmcguire/ambient-weather-local-exporter/pkg/ambient/config"
)

// Attempts to complete missing fields that may not
// be set by a specific provider, such as DewPoint and WindChill
func (u *WeatherUpdate) Enrich(weatherStations ...*config.WeatherStation) {
	if u == nil {
		return
	}

	if u.WindChillF == nil && u.TempOutdoorF != nil && u.WindSpeedMPH != nil {
		wc := CalculateWindChill(*u.TempOutdoorF, *u.WindSpeedMPH)
		u.WindChillF = &wc
	}

	if u.DewPointF == nil && (u.TempOutdoorF != nil && u.HumidityOudoor != nil) {
		if *u.TempOutdoorF != 0 || *u.HumidityOudoor != 0 {
			dp := CalculateDewPoint(*u.TempOutdoorF, float64(*u.HumidityOudoor))
			u.DewPointF = &dp
		}
	}

	if u.BaromAbsoluteIn == nil && u.BaromRelativeIn != nil {
		u.BaromAbsoluteIn = u.BaromRelativeIn
	}
}

func CalculateDewPoint(tempF, humidity float64) float64 {
	// Convert temperature from Fahrenheit to Celsius
	tempC := (tempF - 32) * 5 / 9

	// Calculate the dew point using the Magnus-Tetens approximation
	a := float64(17.27)
	b := float64(237.7)

	alpha := (a*tempC)/(b+tempC) + math.Log(humidity/100)
	dewPointC := (b * alpha) / (a - alpha)

	// Convert dew point back to Fahrenheit
	dewPointF := (dewPointC * 9 / 5) + 32
	return dewPointF
}

func CalculateWindChill(tempF float64, windSpeedMPH float64) float64 {
	if windSpeedMPH <= 3 {
		// Wind chill calculation doesn't apply for very low wind speeds
		return tempF
	}

	// Formula for calculating wind chill
	return 35.74 + 0.6215*tempF -
		35.75*math.Pow(windSpeedMPH, 0.16) +
		0.4275*tempF*math.Pow(windSpeedMPH, 0.16)
}

// Helper function to set values from fields
// typically from a WeatherUpdate
func SetURLVal(vals *url.Values, key string, value any) {
	if value == nil {
		return
	}

	switch v := value.(type) {
	case *float64:
		if v == nil {
			return
		}
		str := strconv.FormatFloat(*v, 'f', 4, 64)
		vals.Set(key, str)
	case *int:
		if v == nil {
			return
		}
		str := strconv.FormatInt(int64(*v), 10)
		vals.Set(key, str)
	case *string:
		if v == nil {
			return
		}
		vals.Set(key, *v)
	}
}