Google Map Data Algorithm

Use the Google map API to create a map for a project. Then I studied Google's image access. Algorithm It is not very difficult.
Let's take a look at our school chart.
Google Maps and Google Earth each level of each image has a URL, for example, the following figure of our school is the address of the http://kh.google.com/kh? V = 3 & t = trstrqqrsstttqtss (this is the image URL)

The variable v = 3 in the URL indicates that the projection algorithm of the satellite map uses the Mercator projection algorithm, and V = 2 indicates another algorithm (not supported)

Variable T = trstrqqrsstttqtssThis is the encoding of this image. The trstrqqrsstttqtss is calculated by an algorithm similar to the Q-tree. He uses the upper left, upper right, lower left, and lower right of an imageQ, R, t, sRespectively. Then recursion is performed in turn. The top layer isT.

If I want to see the top-level world map, the code is "T" and the URL is as follows:
Http://kh.google.com/kh? V = 3 & t = T click the link on the left and you will see the world map (maximum level ).

If I continue to find the graph of China (in fact, the upper right corner of the graph), the encoding is "TR" and the URL is as follows:
Http://kh.google.com/kh? V = 3 & t = tr click the link on the left to view the upper-right corner of the world map (that is, the area that contains China ).
And so on, you can find the map where you want to find it. (It is a simple explanation of this operation. The upper right corner uses a yellow box to indicate "r ")

The following is a tool in which you enter your latitude and longitude, And it will automatically recursion each image. You can step by step look at how Google Maps finds your location. Http://intepid.com/stuff/gmkh/

For more information about Q-tress, refer to this data structure book. The following figure is what I found in Wikipedia.

Below is the JavaScript code for this algorithmProgram(Including encoding and latitude and longitude)

Function Getquadtreeaddress ( Long, lat ) { VaR Pi = 3.1415926535897 ; VaR Digits = 18 ; // How many digits precision // Now convert to normalized square coordinates // Use standard equations to map into Mercator projection VaR X = ( 180.0 + Parsefloat ( Long )) / 360.0 ; VaR Y =- Parsefloat ( Lat ) * PI/ 180 ; // Convert to radians Y = 0.5 * Math. Log (( 1 + Math. Sin ( Y )) / ( 1 - Math. Sin ( Y ))); Y * = 1.0 / ( 2 * Pi ); // Scale factor from radians to normalized Y + = 0.5 ; // And make y range from 0-1 VaR Quad = "T" ; // Google addresses start with T VaR Lookup = "Qrts" ; // TL tr BL br While ( Digits- ) // (Post-Decrement) { // Make sure we only look at fractional part X-= Math. Floor ( X ); Y-= Math. Floor ( Y ); Quad = quad + Lookup. Substr (( X> = 0.5 ? 1 : 0 ) + ( Y> = 0.5 ? 2 : 0 ) , 1 ); // Now descend into that square X * = 2 ; Y * = 2 ; } Return Quad ; }

For more information, see:
Http://intepid.com/2005-07-17/21.50/