如何转换为谷歌编码的折线算法格式？

Question

Google 地图的encoded polyline format 存储纬度/经度信息以及缩放级别。

我有一个包含纬度/经度对的巨大文本文件，我想将其转换为这种格式并用于折线的不同部分（即我需要执行批量转换）

有人知道执行此操作的代码吗？

Answer 1

编码和解码折线的权威参考由 Mark McClure 教授撰写，http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/

它包含实用程序、对算法的讨论以及将 Javascript 代码移植到 Perl、Ruby、PHP、Java 和 Mathematica 中。

注意：对于第 3 版，您不需要第 2 版所需的 levels 字符串。第 3 版自己制定了级别。

Answer 2

我不知道你需要什么语言。你可以从谷歌here得到大致的想法。但是，我发现这些说明并不是 100% 准确的。这就是我的理解，使用同一文本中的示例。我用Java实现的，应该很容易转换成JavaScript或PHP。

  public class MapMath {
    private final static double MULTIPLIER = 100000;
    private final static int FIVE_BIT_MASK = 0x1f;

    public MapMath() {
      double[][] coords = new double[][]{
        {-12.422187,130.854922},
          {-12.422445,130.854937},
          {-12.422234,130.854886}
      };

      StringBuilder encodedStrings = new StringBuilder();
      for (int i = 0; i < 3; i++){
        encodedStrings.append(
            encodeCoordinate(coords[i][0]) + 
            encodeCoordinate(coords[i][1]) + "\n"
            );
      }
      System.out.println(encodedStrings);
    }

    private String encodeCoordinate(double coordinate) {
      StringBuilder encodedCoordinate = new StringBuilder();
      boolean hasNext;

      coordinate *= MULTIPLIER;
      int value = (int) coordinate;
      value <<= 1;
      if(coordinate < 0) value = ~value;  

      do {
        int next = (value >> 5);
        hasNext = (next > 0);
        int encVal = value & FIVE_BIT_MASK;
        if(hasNext) encVal |= 0x20;
        encVal += 0x3f;
        value = next;
        encodedCoordinate.append((char)(encVal));
      } while (hasNext);

      return encodedCoordinate.toString();
    } 

    public static double toRadians(double degrees) {
      return (degrees*Math.PI)/180;
    }

    public static void main(String[] args){
      new MapMath();
    }
  }

请注意，连续坐标应该是前一个坐标的偏移量。 希望它对您有用，如果需要任何进一步的帮助，请告诉我。

Answer 3

我还看到了一些不太准确的算法实现（也有一些非常糟糕的代码）。这是我的编码函数（用 VB.NET 编写）。此函数仅对传递给它的一个值进行编码，因此您必须在其他地方进行所有差异计算。返回的结果与 Google 的 Encoded Polyline Algorithm Format 页面上显示的结果完全一致。 （我的一些代码可以被压缩和优化，但我试图让算法的每一步都清晰）。我希望有人觉得这很有用！

''' <summary>
''' Encodes a latitude or longitude value by using Google's Polyline algorithm
''' </summary>
''' <param name="ToEnc">Latitude or Longitude to encode (or a difference value) (Single)</param>
''' <returns>Polyline encoded point (String)</returns>
''' <remarks>This function doesn't care what value you pass it, whether it's an absolute coordinate or a difference.  Make sure you do all of the point difference calculations somewhere else before calling this method.</remarks>
Private Function Encode(ByVal ToEnc As Single) As String
    Dim Coord As Integer 'The integer version of the coordinate, as per steps 2 and 3
    Dim B(5) As Byte 'The 5-bit chunks, as per steps 6 and 7.  Note that all 6 bytes may not be used
    Dim I As Integer 'Generic counter
    Dim C(5) As Char 'The chunks converted from bytes to characters

    '2., 3. Take the decimal value and multiply is by 1e5, rounding the result.  Convert the decimal value to binary.
    Coord = Math.Sign(ToEnc) * Int(Math.Abs(ToEnc) * 100000.0)

    '4. Left-shift the binary value one bit
    Coord <<= 1

    '5. If the original decimal value is negative, invert this encoding
    If ToEnc < 0 Then Coord = Not Coord

    '6. Break the binary value out into 5-bit chunks (starting from the right hand side)
    '7. Place the 5-bit chunks in reverse order
    'Steps 6 and 7 are done at the same time
    B(0) = Coord And &H1F
    B(1) = (Coord And &H3E0) >> 5
    B(2) = (Coord And &H7C00) >> 10
    B(3) = (Coord And &HF8000) >> 15
    B(4) = (Coord And &H1F00000) >> 20
    B(5) = (Coord And &H3E000000) >> 25

    '8. OR each value with 0x20 if another bit chunk follows
    'Go through the 5-bit chunks looking for the first one that isn't zero
    'When we find it, that means the one BEFORE that is the last to get the 0x20 modification
    Dim E As Integer = -1 'Penultimate byte that contains data, the last one to get ORed by 0x20
    For I = 5 To 1 Step -1
        If B(I) <> 0 Then
            'This is the first nonzero value we've encountered, so keep track of this position and exit the loop
            E = I - 1
            Exit For
        End If
    Next
    'Apply the 0x20 modification
    For I = 0 To E
        B(I) = B(I) Or &H20
    Next

    '10. Add 63 to each value
    For I = 0 To 5
        If B(I) > 0 Then B(I) += 63
    Next

    '11. Convert each value to its ASCII equivalent
    For I = 0 To 5
        C(I) = Chr(B(I))
    Next

    'Turn the char array into a string and return it
    Return New String(C, 0, E + 2)
End Function

Answer 4

这里有一个很好的 PHP 实现：

https://github.com/tonydspaniard/Yii-extensions/blob/master/extensions/EGMap/EGMapPolylineEncoder.php

它基于http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/ 上提供的一些代码，但经过完善，形成了适当的类。

Answer 5

感谢乔纳森， 通过一些调整，我的 VBA 版本在这里.... 位移取自这里... http://www.excely.com/excel-vba/bit-shifting-function.shtml#.UoUFM8ZSiSo

   ''' <summary>
''' Encodes a latitude or longitude value by using Google's Polyline algorithm
''' </summary>
''' <param name="ToEnc">Latitude or Longitude to encode (or a difference value) (Single)</param>
''' <returns>Polyline encoded point (String)</returns>
''' <remarks>This function doesn't care what value you pass it, whether it's an absolute coordinate or a difference.  Make sure you do all of the point difference calculations somewhere else before calling this method.</remarks>
Function Encode(ByVal ToEnc As Single) As String
    Dim Coord As Double 'The integer version of the coordinate, as per steps 2 and 3
    Dim B(5) As Byte 'The 5-bit chunks, as per steps 6 and 7.  Note that all 6 bytes may not be used
    Dim i As Integer 'Generic counter
    Dim C(5) As String 'The chunks converted from bytes to characters
    Dim E As Integer
    E = -1 'Penultimate byte that contains data, the last one to get ORed by 0x20

    '2., 3. Take the decimal value and multiply is by 1e5, rounding the result.  Convert the decimal value to binary.
    Coord = Math.Sgn(ToEnc) * Int(Math.Abs(ToEnc) * 100000)

    '4. Left-shift the binary value one bit
    Coord = shl(Coord, 1)

    '5. If the original decimal value is negative, invert this encoding
    If ToEnc < 0 Then Coord = Not Coord

    '6. Break the binary value out into 5-bit chunks (starting from the right hand side)
    '7. Place the 5-bit chunks in reverse order
    'Steps 6 and 7 are done at the same time
    B(0) = Coord And &H1F
    B(1) = shr((Coord And &H3E0), 5)
    B(2) = shr((Coord And &H7C00), 10)
    B(3) = shr((Coord And &HF8000), 15)
    B(4) = shr((Coord And &H1F00000), 20)
    B(5) = shr((Coord And &H3E000000), 25)

    '8. OR each value with 0x20 if another bit chunk follows
    'Go through the 5-bit chunks looking for the first one that isn't zero
    'When we find it, that means the one BEFORE that is the last to get the 0x20 modification
    For i = 5 To 1 Step -1
        If B(i) <> 0 Then
            'This is the first nonzero value we've encountered, so keep track of this position and exit the loop
            E = i - 1
            Exit For
        End If
    Next
    'Apply the 0x20 modification
    For i = 0 To E
        B(i) = B(i) Or &H20
    Next

    '10. Add 63 to each value
    For i = 0 To 5
        If B(i) > 0 Then B(i) = B(i) + 63
    Next

    '11. Convert each value to its ASCII equivalent
    For i = 0 To 5
        C(i) = Chr(B(i))
    Encode = Encode + C(i)
    Next

    'Turn the char array into a string and return it
 End Function

Public Function shr(ByVal Value As Long, ByVal Shift As Byte) As Long
    Dim i As Byte
    shr = Value
    If Shift > 0 Then
        shr = Int(shr / (2 ^ Shift))
    End If
End Function
Public Function shl(ByVal Value As Long, ByVal Shift As Byte) As Long
    shl = Value
    If Shift > 0 Then
        Dim i As Byte
        Dim m As Long
        For i = 1 To Shift
            m = shl And &H40000000
            shl = (shl And &H3FFFFFFF) * 2
            If m <> 0 Then
                shl = shl Or &H80000000
            End If
        Next i
    End If
End Function