routing-service/encoding/polylines/encoding.go

package polylines

import (
	"github.com/paulmach/orb"
	"github.com/twpayne/go-polyline"
)

// // Encode encodes coordinates to the "Encoded Polyline Algorithm Format"
// // More info: https://developers.google.com/maps/documentation/utilities/polylinealgorithm
// // points: points of the polyline
// // precision: usually 5 or 6; Google's original algorithm uses 5 digits of decimal precision,
// // which is accurate to about a meter. A precision of 6 gives you an accuracy of about 10cm
// // more info: https://mapzen.com/blog/polyline-precision/
// func Encode(linestring orb.LineString, precision uint32) string {

// 	encoded := ""

// 	latitude := 0.0
// 	longitude := 0.0

// 	for _, point := range linestring {
// 		polyLatitude := encodeElement(point.Lat()-latitude, precision)
// 		encoded += polyLatitude

// 		polyLongitude := encodeElement(point.Lon()-longitude, precision)
// 		encoded += polyLongitude

// 		// to conserve space, points only include the offset from the previous point
// 		latitude = point.Lat()
// 		longitude = point.Lon()

// 	}

// 	return encoded

// }

// // Encode5 is a short call for Encode with precision set to 5
// // Accuracy is about one meter
// func Encode5(linestring orb.LineString) string {
// 	return Encode(linestring, 5)
// }

// // Encode6 is a short call for Encode with precision set to 6
// // Accuracy is about ten centimeters
// func Encode6(linestring orb.LineString) string {
// 	return Encode(linestring, 6)
// }

// // encodeElement encodes an coordinate element (i.e. latitude or longitude)
// // to the "Encoded Polyline Algorithm Format"
// func encodeElement(element float64, precision uint32) string {

// 	elementInt := int32(math.Round(element * math.Pow10(int(precision))))
// 	elementInt = elementInt << 1
// 	if element < 0 {
// 		elementInt = ^elementInt
// 	}

// 	var c chunks
// 	c.Parse(elementInt)

// 	return c.String()

// }

// // round n to precision digits
// func round(n float64, precision uint32) float64 {

// 	factor := math.Pow10(int(precision))
// 	return math.Round(n*factor) / factor

// }

func Encode(line orb.LineString, precision uint32) string {

	preparedLine := [][]float64{}

	for _, point := range line {
		preparedLine = append(preparedLine, []float64{point.Lat(), point.Lon()})
	}

	return string(polyline.EncodeCoords(preparedLine))
}