85 lines
2.3 KiB
Go
85 lines
2.3 KiB
Go
package polylines
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import (
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"github.com/paulmach/orb"
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"github.com/twpayne/go-polyline"
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)
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// // Encode encodes coordinates to the "Encoded Polyline Algorithm Format"
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// // More info: https://developers.google.com/maps/documentation/utilities/polylinealgorithm
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// // points: points of the polyline
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// // precision: usually 5 or 6; Google's original algorithm uses 5 digits of decimal precision,
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// // which is accurate to about a meter. A precision of 6 gives you an accuracy of about 10cm
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// // more info: https://mapzen.com/blog/polyline-precision/
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// func Encode(linestring orb.LineString, precision uint32) string {
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// encoded := ""
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// latitude := 0.0
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// longitude := 0.0
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// for _, point := range linestring {
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// polyLatitude := encodeElement(point.Lat()-latitude, precision)
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// encoded += polyLatitude
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// polyLongitude := encodeElement(point.Lon()-longitude, precision)
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// encoded += polyLongitude
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// // to conserve space, points only include the offset from the previous point
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// latitude = point.Lat()
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// longitude = point.Lon()
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// }
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// return encoded
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// }
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// // Encode5 is a short call for Encode with precision set to 5
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// // Accuracy is about one meter
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// func Encode5(linestring orb.LineString) string {
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// return Encode(linestring, 5)
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// }
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// // Encode6 is a short call for Encode with precision set to 6
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// // Accuracy is about ten centimeters
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// func Encode6(linestring orb.LineString) string {
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// return Encode(linestring, 6)
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// }
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// // encodeElement encodes an coordinate element (i.e. latitude or longitude)
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// // to the "Encoded Polyline Algorithm Format"
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// func encodeElement(element float64, precision uint32) string {
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// elementInt := int32(math.Round(element * math.Pow10(int(precision))))
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// elementInt = elementInt << 1
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// if element < 0 {
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// elementInt = ^elementInt
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// }
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// var c chunks
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// c.Parse(elementInt)
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// return c.String()
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// }
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// // round n to precision digits
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// func round(n float64, precision uint32) float64 {
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// factor := math.Pow10(int(precision))
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// return math.Round(n*factor) / factor
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// }
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func Encode(line orb.LineString, precision uint32) string {
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preparedLine := [][]float64{}
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for _, point := range line {
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preparedLine = append(preparedLine, []float64{point.Lat(), point.Lon()})
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}
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return string(polyline.EncodeCoords(preparedLine))
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}
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