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