projtrans.go

package main

import (
	"fmt"
	"math"
)

func toWGS84(xLon, yLat float64) (lon, lat float64) {

    // Check if coordinate out of range for Web Mercator
    // 20037508.3427892 is full extent of Web Mercator
    if (math.Abs(xLon) > 20037508.3427892) || (math.Abs(yLat) > 20037508.3427892) {
    	return
    }
        
 
    semimajorAxis := 6378137.0  // WGS84 spheriod semimajor axis
 
    lat = (1.5707963267948966 - (2.0 * math.Atan(math.Exp((-1.0 * yLat) / semimajorAxis)))) * (180/math.Pi)
    lon = ((xLon / semimajorAxis) * 57.295779513082323) - ((math.Floor((((xLon / semimajorAxis) * 57.295779513082323) + 180.0) / 360.0)) * 360.0)
 
    return
}

func toWebMercator(xLon, yLat float64) (easting, northing float64) {
    // Check if coordinate out of range for Latitude/Longitude
    if (math.Abs(xLon) > 180) && (math.Abs(yLat) > 90) {
    	return
    }
        
 
    semimajorAxis := 6378137.0  // WGS84 spheriod semimajor axis
    east := xLon * 0.017453292519943295
    north := yLat * 0.017453292519943295
 
    northing = (semimajorAxis / 2) * math.Log((1.0 + math.Sin(north)) / (1.0 - math.Sin(north)))
    easting = semimajorAxis * east
 
    return
}

func main() {
	fmt.Println(toWebMercator(-105.816001, 40.067633))
	fmt.Println(toWGS84(-11779383.349100526, 4875775.395628653))
}