System and method for converting source image data to tile data

#Systems and methods disclosed herein relate generally to tile-based mapping systems. The first web-based mapping systems offered rudimentary mapping applications through a web browser. A first type of system allowed simple map movements by requiring a user to click on navigation arrow buttons surrounding the map view. When a user clicked on an arrow, the map moved a predetermined amount in the direction clicked. There were also buttons for zooming in and out. Other map applications allowed users to drag and draw boxes on the map to relocate the map view. These applications had several disadvantages, including slow rendering and downloading of map views, because the map view was often represented by a single large image file. Each time the map was moved to the left or right, the entire image was re-rendered and re-sent to the client even though only a portion of the image was new. However, the interfaces were well suited to early web browsers, the map interface could be written entirely in HTML or with minimal JavaScript, and since all navigations were fixed, map servers could cache rendered maps. A second type of system adopted a map view and navigation style similar to desktop GIS systems which used browser plug-in technology and development platforms like Java or Flash.

#GOOGLE MAPS® introduced the “slippy map” interface that allows users to move and zoom the map, and was written in HTML and JavaScript. A key technology behind the “slippy map” interface was the concept of tile-based mapping. Mapping applications were made responsive by using background maps that had been broken into smaller tiled images. Those tiles were stored, already rendered, on a central server. Because they were already rendered, they could be sent to clients quickly. The tiles were discretely addressed so they could be cached by interne caching services and by clients' own browsers. The map images were broken into smaller pieces so that when users navigated the map view, only the new parts of the map had to be resent from the server.

#Tile-based mapping systems are based on multiple discrete zoom levels, each corresponding to a fixed map scale. In tile-based mapping systems, multiple image tiles are used to virtualize a single map view, and image tiles are accessible using a discrete addressing scheme. Also, in tile-based mapping systems, tiled images stored on a server system are sent to a client system with minimal processing, i.e. as much processing is done ahead of time as possible. Optionally, although not required in tile-based mapping systems, tile addressing can follow a single global projection, tiles can be distributed using a client/server system architecture, and tiles can be organized into relatively few, fixed layers. Tile images can be of any size, and can vary from map scale to map scale, or can vary across the same scale or be random in size. What is needed is a system to determine which size is most efficient for a specific purpose.

#FIG. 1A PRIOR ART is a hierarchical block diagram of layers, scales, columns, and tiles;

#FIG. 1B PRIOR ART is a pictorial diagram of three zoom levels;

#FIG. 2 is a pictorial diagram of the earth mapped to a two-dimensional surface, and with a grid overlain upon the surface;

#The problems set forth above as well as further and other problems are solved by the present teachings. These solutions and other advantages are achieved by the various embodiments of the teachings described herein below.

#Referring now to FIG. 2, tile-based mapping systems map positions on the earth 11 to a two-dimensional surface 13 and divide that surface into a series of regularly spaced grids 15. Map tiles are discretely addressed, and a translation method between tile addresses and a continuous geospatial coordinate system is defined. This logical tile scheme forms a multi-resolution, regularly spaced grid that is tied to a single two-dimensional map projection which allows a tiled image to be accessed directly with discrete coordinates. For example, instead of requesting a map image with a bounding rectangle delineated with continuous real numbers like [−100.0, 30.00] to [−80.0, 40.0], a tile can be requested from a grid with zoom level, column, and row addresses delineated with discrete integer values.

#Referring now to FIG. 3A, there is a mapping between the address of a tile to the geospatial coordinates for the area covered by the tile. One possible way to do this, for example, is to start with a geodetic projection which portrays the earth as a rectangle 360° wide and 180° tall. In this case, the base projection and the logical tile scheme have 2-to-1 aspect ratios. At zoom level one 17, the logical tile scheme has one row and two columns. Each subsequent zoom level, for example, zoom level two 19, has double the number of rows and columns and four times the number of tiles as the previous zoom level. At each increase in zoom level, each tile is divided into four sub-tiles. Although there is no theoretical maximum number of zoom levels, the practical limit is twenty. The number of columns for a zoom level i is 2i and the number of rows is 2i-1. Referring now to FIG. 3B, the tile address can be related to a geographic bounding rectangle as per equations 21 and 23.