Google Maps quad-tree Encoding

WebGIS of map cutting method, such GoogleMapIs a common method of map service websites. Big GIS platforms, such as ArcIMS, have also added tilemap technology in the new version.
The satellite data provided by Google Maps can reach a precision of less than 1 meter for image data in many cities. Satellite images are obtained by Mercator projection using an equal-angular tangent column. The obtained images are pre-modeled in pyramid mode and stored hierarchically according to different precision. Google Maps provides a total of 0 ~ 17. A total of 18 scaling levels. All satellite images are sliced into image blocks of 256x256 pixels, which are encoded and indexed by the quad-tree method, then, the image block is spliced on the browser based on the Coordinate Position and precision of the user request to form a large satellite image. The coordinates of Google Maps are indexed and encoded using the four letters qrts. That is, the top left, bottom left, top right, and bottom right of an image are represented by Q, T, R, and s, respectively, the image is split into four parts marked by different letters. The image is refined step by step based on the location and accuracy of the user request, and is recursively written. First, we convert the longitude and latitude to radians. After normalization, the variation interval is between 0 and ~ Within the range of 1, and then determine the number of iterations based on the expected precision series. Then, based on the calculation formula, for example, after converting the longitude and latitude of Beijing, the Google coordinate string of the Beijing Center is trstrqqrqssttttrrrstq. When the variable v = 3 in the URL indicates that the satellite map projection adopts the Mercator projection algorithm; when v = 2, it indicates another projection algorithm, but it is no longer supported currently. Access the preceding address in the browser to obtain a 256x256 pixel Beijing satellite image.