Implementation of Google Maps API encoding line algorithm

Implementation of Google Maps API encoding line algorithm

 

 

In the secondary development of Google Maps API, we encountered the encoding line algorithm problem through gpolyline. fromencoded can effectively improve the rendering speed. based on the fact that there is no relevant implementation on the internet, I will give the algorithm of latitude and longitude and level in the encoding line for your reference. it is implemented using MFC and Standard C. You can modify the relevant code in other environments.

 

 

1. Convert binary to decimal (8 digits)

 

Inline int bintodec (char * B)
{
Int I, j, V;
V = 0;
Int Len = strlen (B );
If (LEN <1) return V;
I = 0; V = 0; j = 0;
For (I = len-1; I> = 0; I --)
{
If (B [I] = '1 ')
V + = (INT) Pow (2, J );
J ++;
}
Return V;
}

 

Ii. Related Algorithms

 

1. Latitude and longitude Algorithms

Cstring polyline_lonlat_encode (double num)
{
Int m, I;
Cstring S;

Int d [8];

Char m_buf [8] [6];
Int n = 32;
Char Buf [256] = {0 };
Bool is_negative = false;
Double T = num;

// Fine-tune data to prevent data distortion
T + = (T <1e-8 )? -1:1) * 1e-8;
T * = 1e5;
M = int (t );
If (M <0) is_negative = true;

// Convert decimal to binary
For (I = 0; I <n; I ++)
{
If (1 <(n-i-1) & M)
Buf [I] = '1 ';
Else
Buf [I] = '0 ';
}

// Calculate the anticode and add the suffix 1 (negative number is 1, positive number is 0)
If (is_negative)
{
For (I = 0; I <n; I ++)
{
If (BUF [I] = '0 ')
Buf [I] = '1 ';
Else
Buf [I] = '0 ';

}
}
S = Buf;
S + = is_negative? "1": "0 ";
// Remove the front-end 0, starting from 1
I = S. Find ("1", 0 );
If (I! =-1)
S = S. Right (S. getlength ()-I );

Else

S = "0 ";

// Computing Group (a group of five digits)

M = S. getlength ()/5;
If (M * 5 <S. getlength ())
M + = 1;
// XOR 0x20 (not used in the last group) before grouping data, add 63
For (I = 0; I <m; I ++)
{
Sprintf (m_buf [I], "% s", S. Right (5 ));
If (I = m-1)
D [I] = bintodec (m_buf [I]) + 63;
Else
D [I] = bintodec (m_buf [I]) + 32 + 63;

S = S. Left (S. getlength ()-5 );
}

// Convert to ASCII
S = "";
For (I = 0; I <m; I ++)
{
S + = toascii (d [I]);
}
Return S;
}

2. encoding-level Algorithms

Cstring polyline_level_encode (INT level)

{
Int m, I;
Cstring S;

Int d [8];

Char m_buf [8] [6];
Int n = 32;
Char Buf [256] = {0 };

M = level;

// Convert decimal to binary
For (I = 0; I <n; I ++)
{
If (1 <(n-i-1) & M)
Buf [I] = '1 ';
Else
Buf [I] = '0 ';
}

// Calculate the anticode and add the suffix 1 (negative number is 1, positive number is 0)
If (is_negative)
{
For (I = 0; I <n; I ++)
{
If (BUF [I] = '0 ')
Buf [I] = '1 ';
Else
Buf [I] = '0 ';

}
}
S = Buf;
// Remove the front-end 0, starting from 1
I = S. Find ("1", 0 );
If (I! =-1)
S = S. Right (S. getlength ()-I );

Else

S = "0 ";

// Computing Group (a group of five digits)

M = S. getlength ()/5;
If (M * 5 <S. getlength ())
M + = 1;
// XOR 0x20 (not used in the last group) before grouping data, add 63
For (I = 0; I <m; I ++)
{
Sprintf (m_buf [I], "% s", S. Right (5 ));
If (I = m-1)
D [I] = bintodec (m_buf [I]) + 63;
Else
D [I] = bintodec (m_buf [I]) + 32 + 63;

S = S. Left (S. getlength ()-5 );
}

// Convert to ASCII
S = "";
For (I = 0; I <m; I ++)
{
S + = toascii (d [I]);
}
Return S;
}

 

Iii. Call description

 

Afxmessagebox ("level:" + polyline_level_encode (16 ));
Afxmessagebox ("points (38.5-120.2), (40.7,-120.95), (43.252,-126.453):" +

Polyline_lonlat_encode (38.5) + polyline_lonlat_encode (-120.2) +

Polyline_lonlat_encode (40.7-38.5) +

Polyline_lonlat_encode (-120.95 + 120.2) +

Polyline_lonlat_encode (43.252-40.7) +

Polyline_lonlat_encode (-126.453 + 120.95 ));

 

Iv. Description

1. For the encoding line algorithm format, see Encoding

2. sprintf, toascii, and pow are standard C functions.

 

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