initial commit

encoding/polylines/decoding.go

@@ -0,0 +1,63 @@
+package polylines
+
+import (
+	"math"
+
+	"github.com/paulmach/orb"
+)
+
+func Decode(encoded *string, precisionOptional ...int) orb.LineString {
+	// default to 6 digits of precision
+	precision := 6
+	if len(precisionOptional) > 0 {
+		precision = precisionOptional[0]
+	}
+	factor := math.Pow10(precision)
+
+	// Coordinates have variable length when encoded, so just keep
+	// track of whether we've hit the end of the string. In each
+	// loop iteration, a single coordinate is decoded.
+	lat, lng := 0, 0
+	var coordinates orb.LineString
+	index := 0
+	for index < len(*encoded) {
+		// Consume varint bits for lat until we run out
+		var byte int = 0x20
+		shift, result := 0, 0
+		for byte >= 0x20 {
+			byte = int((*encoded)[index]) - 63
+			result |= (byte & 0x1f) << shift
+			shift += 5
+			index++
+		}
+
+		// check if we need to go negative or not
+		if (result & 1) > 0 {
+			lat += ^(result >> 1)
+		} else {
+			lat += result >> 1
+		}
+
+		// Consume varint bits for lng until we run out
+		byte = 0x20
+		shift, result = 0, 0
+		for byte >= 0x20 {
+			byte = int((*encoded)[index]) - 63
+			result |= (byte & 0x1f) << shift
+			shift += 5
+			index++
+		}
+
+		// check if we need to go negative or not
+		if (result & 1) > 0 {
+			lng += ^(result >> 1)
+		} else {
+			lng += result >> 1
+		}
+
+		// scale the int back to floating point and storeLineString it
+		coordinates = append(coordinates, orb.Point{float64(lat) / factor, float64(lng) / factor})
+	}
+
+	return coordinates
+}

encoding/polylines/encoding.go

@@ -0,0 +1,17 @@
+package polylines
+
+import (
+	"github.com/paulmach/orb"
+	"github.com/twpayne/go-polyline"
+)
+
+func Encode(line orb.LineString) string {
+
+	preparedLine := [][]float64{}
+
+	for _, point := range line {
+		preparedLine = append(preparedLine, []float64{point.Lon(), point.Lat()})
+	}
+
+	return string(polyline.EncodeCoords(preparedLine))
+}