main.go

package coordtransform

import (
	"math"
)

// WGS84坐标系：即地球坐标系，国际上通用的坐标系。
// GCJ02坐标系：即火星坐标系，WGS84坐标系经加密后的坐标系。Google Maps，高德在用。
// BD09坐标系：即百度坐标系，GCJ02坐标系经加密后的坐标系。

const (
	X_PI   = math.Pi * 3000.0 / 180.0
	OFFSET = 0.00669342162296594323
	AXIS   = 6378245.0
)

//BD09toGCJ02 百度坐标系->火星坐标系
func BD09toGCJ02(lon, lat float64) (float64, float64) {
	x := lon - 0.0065
	y := lat - 0.006

	z := math.Sqrt(x*x+y*y) - 0.00002*math.Sin(y*X_PI)
	theta := math.Atan2(y, x) - 0.000003*math.Cos(x*X_PI)

	gLon := z * math.Cos(theta)
	gLat := z * math.Sin(theta)

	return gLon, gLat
}

//GCJ02toBD09 火星坐标系->百度坐标系
func GCJ02toBD09(lon, lat float64) (float64, float64) {
	z := math.Sqrt(lon*lon+lat*lat) + 0.00002*math.Sin(lat*X_PI)
	theta := math.Atan2(lat, lon) + 0.000003*math.Cos(lon*X_PI)

	bdLon := z*math.Cos(theta) + 0.0065
	bdLat := z*math.Sin(theta) + 0.006

	return bdLon, bdLat
}

//WGS84toGCJ02 WGS84坐标系->火星坐标系
func WGS84toGCJ02(lon, lat float64) (float64, float64) {
	if isOutOFChina(lon, lat) {
		return lon, lat
	}

	mgLon, mgLat := delta(lon, lat)

	return mgLon, mgLat
}

//GCJ02toWGS84 火星坐标系->WGS84坐标系
func GCJ02toWGS84(lon, lat float64) (float64, float64) {
	if isOutOFChina(lon, lat) {
		return lon, lat
	}

	mgLon, mgLat := delta(lon, lat)

	return lon*2 - mgLon, lat*2 - mgLat
}

//BD09toWGS84 百度坐标系->WGS84坐标系
func BD09toWGS84(lon, lat float64) (float64, float64) {
	lon, lat = BD09toGCJ02(lon, lat)
	return GCJ02toWGS84(lon, lat)
}

//WGS84toBD09 WGS84坐标系->百度坐标系
func WGS84toBD09(lon, lat float64) (float64, float64) {
	lon, lat = WGS84toGCJ02(lon, lat)
	return GCJ02toBD09(lon, lat)
}

func delta(lon, lat float64) (float64, float64) {
	dlat, dlon := transform(lon-105.0, lat-35.0)
	radlat := lat / 180.0 * math.Pi
	magic := math.Sin(radlat)
	magic = 1 - OFFSET*magic*magic
	sqrtmagic := math.Sqrt(magic)

	dlat = (dlat * 180.0) / ((AXIS * (1 - OFFSET)) / (magic * sqrtmagic) * math.Pi)
	dlon = (dlon * 180.0) / (AXIS / sqrtmagic * math.Cos(radlat) * math.Pi)

	mgLat := lat + dlat
	mgLon := lon + dlon

	return mgLon, mgLat
}
func transform(lon, lat float64) (x, y float64) {
	var lonlat = lon * lat
	var absX = math.Sqrt(math.Abs(lon))
	var lonPi, latPi = lon * math.Pi, lat * math.Pi
	var d = 20.0*math.Sin(6.0*lonPi) + 20.0*math.Sin(2.0*lonPi)
	x, y = d, d
	x += 20.0*math.Sin(latPi) + 40.0*math.Sin(latPi/3.0)
	y += 20.0*math.Sin(lonPi) + 40.0*math.Sin(lonPi/3.0)
	x += 160.0*math.Sin(latPi/12.0) + 320*math.Sin(latPi/30.0)
	y += 150.0*math.Sin(lonPi/12.0) + 300.0*math.Sin(lonPi/30.0)
	x *= 2.0 / 3.0
	y *= 2.0 / 3.0
	x += -100.0 + 2.0*lon + 3.0*lat + 0.2*lat*lat + 0.1*lonlat + 0.2*absX
	y += 300.0 + lon + 2.0*lat + 0.1*lon*lon + 0.1*lonlat + 0.1*absX
	return
}

func isOutOFChina(lon, lat float64) bool {
	return !(lon > 72.004 && lon < 135.05 && lat > 3.86 && lat < 53.55)
}