CN102819530A - Method and device for displaying electronic map - Google Patents

Abstract

The invention discloses a method and device for displaying an electronic map. The method includes the following steps: downloading the tile map of the electronic map in advance, and storing the tile map locally in the form of a multi-level directory index; receiving a query request, determining Query the tile map corresponding to the request; obtain the tile map locally, organize and display the tile map. The user experience is improved through the present invention.

Description

Electronic map display method and device

technical field

The present invention relates to the communication field, in particular to a method and device for displaying an electronic map.

Background technique

With the emergence of tile map technology, many Internet electronic map providers (for example, Google, Yahoo, Baidu) have used the technology of tile map, which makes the dragging of the map in the online electronic map service , zooming, and quick browsing at different scales have all been greatly improved.

However, the current Internet electronic map services are all online services, such as direct access through the Web, and indirect access by calling APIs. In this way, there will be a delay in displaying in an environment with poor network conditions, which reduces the user experience. In an environment connected to the Internet, electronic maps cannot be used.

Aiming at the problem of inconvenient use of the electronic map existing in related technologies, no effective solution has been proposed yet.

Contents of the invention

The main purpose of the present invention is to provide a method and device for displaying an electronic map to at least solve the above problems.

According to one aspect of the present invention, a method for displaying an electronic map is provided. The method includes the following steps: downloading the tile map of the electronic map in advance, and storing the tile map in the form of a multi-level directory index in Local: receiving a query request, determining a tile map corresponding to the query request; obtaining the tile map locally, organizing and displaying the tile map.

In the above method, pre-downloading the tile map of the electronic map includes: obtaining the uniform resource locator of the tile map provided by the electronic map service provider; filling the parameters in the uniform resource locator according to the tile map to be downloaded , forming a complete uniform resource locator; downloading the tile map to be downloaded according to the complete uniform resource locator.

In the above method, filling the latitude and longitude in the uniform resource locator according to the tile map that needs to be downloaded includes: converting the global latitude and longitude into a plane coordinate system by using the length of the earth's radius according to the Mercator projection formula; using the plane coordinate system The coordinates to populate the latitude and longitude parameters in the URL.

In the above method, the manner of the multi-level directory index includes: establishing the multi-level directory according to at least one of the following: the type of the electronic map, the latitude and longitude, and the zoom level, wherein the latitude and longitude are expressed as (x, y ), the coordinate system that x and y form is that longitude is converted into a plane coordinate system according to the Mercator projection formula, and the origin is positioned at the upper left corner of the plane coordinate system, and the longitude is converted into the horizontal x axis of the plane coordinate system, and The latitude is converted to the longitudinal y axis of the plane coordinate system. When the maximum zoom level of the tile map of the electronic map is n, the value of x is at most 2n-1, and the value of y is 2n-1 .

In the above method, the method of multi-level directory indexing also includes: each zoom level corresponds to a directory, and the x value of the tile map under the zoom level is divided by M, and the quotient is two in the zoom level directory. level directory name, the remainder is the third-level directory name under the zoom level directory, divide the y value of the tile map under the zoom level by M, the quotient is the fourth-level directory name under the zoom level directory, and the remainder is the The file name of the picture file of the tile map, wherein, the M is a positive integer, and the M corresponds to the zoom level.

In the above method, the M value corresponding to all zoom levels is 1024.

In the above method, determining the tile map corresponding to the query request, obtaining the tile map locally, organizing and displaying the tile map includes: determining the tile according to the zoom level and latitude and longitude in the query request (x, y) of the map and pixel coordinates in the tile map, and convert the pixel coordinates into screen coordinates of the display screen; determine the number of tiles filling the display screen and the coordinates of the display screen Scope; According to the (x, y) of the tile map, obtain the tile map from the local, organize and display the obtained tile map.

In the above method, obtaining the tile map locally, organizing and displaying the tile map further includes: obtaining the data of the tile map from the memory buffer, and obtaining the tile map from the memory In the case of map data, the data of the tile map is loaded from the local memory, and the data of the tile map is stored in the memory buffer.

According to another aspect of the present invention, there is also provided a display device for an electronic map, including: a download module, configured to pre-download the tile map of the electronic map; a storage module, configured to store the tile map in multiple The method of level directory index is stored locally; the query module is used to receive the query request and determine the tile map corresponding to the query request; the display module is used to obtain the tile map locally, organize and display the tiles map.

In the above device, the downloading module includes: an obtaining unit, configured to obtain the URL of the tile map provided by the electronic map service provider; a forming unit, configured to fill the URL with the tile map downloaded as required parameters in the symbol to form a complete uniform resource locator; a downloading unit configured to download the tile map to be downloaded according to the complete uniform resource locator.

In the above device, the storage module is used to establish the multi-level directory according to at least one of the following: the type of the electronic map, the latitude and longitude, and the zoom level, wherein the latitude and longitude are expressed as (x, y), x and The coordinate system composed of y is a coordinate system transformed according to the Mercator projection formula. The origin is located in the upper left corner of the coordinate system. The longitude is converted to the horizontal x-axis of the coordinate system of the plane coordinate system, and the latitude is converted to the plane coordinate system. On the vertical y axis, when the maximum zoom level of the tile map of the electronic map is n, the value of x is at most 2n-1, and the value of y is 2n-1.

Through the present invention, the tile map of the electronic map is downloaded in advance, and the tile map is stored locally in the form of a multi-level directory index; the query request is received, and the tile map corresponding to the query request is determined; the tile map is obtained locally, Organize and display tile maps. The problem of inconvenient use of the electronic map in the prior art is solved, so that the user can still use the electronic map when there is no Internet access, and the user experience is improved.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention. In the attached picture:

FIG. 1 is a flowchart of a method for displaying an electronic map according to an embodiment of the present invention;

Fig. 2 is a structural block diagram of an electronic map display device according to an embodiment of the present invention;

Fig. 3 is a structural block diagram of an electronic map display device according to a preferred embodiment of the present invention;

Fig. 4 is a structural block diagram of an electronic map display device according to another preferred embodiment of the present invention;

Fig. 5 is a schematic diagram of the slice distribution of the map when the zoom level is 1 related to the embodiment of the present invention;

Fig. 6 is a flow chart of downloading and storing tile map data according to a preferred embodiment of the present invention;

Fig. 7 is a schematic diagram of a tile map data organization structure according to a preferred embodiment of the present invention;

FIG. 8 is a flow chart of offline displaying Google Maps according to a preferred embodiment of the present invention.

Detailed ways

Hereinafter, the present invention will be described in detail with reference to the drawings and examples. It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

In the following embodiments, the tile map is taken as an example for illustration. The tile map essentially uses a general-purpose map as the main map background, and stores it on the server side by a pre-generated method. Then, according to different requests submitted by users, the corresponding The map tiles are sent to the client for browsing. Moreover, since the map requested by the client is pre-generated, it does not need to calculate and draw the user's request in real time like traditional WebGIS, so the tile map technology can have the advantage of speed in the display of the map.

Fig. 1 is a flowchart of a method for displaying an electronic map according to an embodiment of the present invention. As shown in Fig. 1, the process includes the following steps:

Step S102, pre-downloading the tile map of the electronic map, and storing the tile map locally in the form of a multi-level directory index;

Step S104, receiving the query request, and determining the tile map corresponding to the query request;

Step S106, obtaining tile maps locally, organizing and displaying the tile maps.

Through the above steps, the tile map can be downloaded in advance, so that the tile map can be directly obtained from the local when using, avoiding the dependence of the electronic map on the network.

For a service provider that provides map services, it must have an interface for downloading tile map data, through which the tile map can be downloaded. Generally speaking, the tile map can be obtained through a Universal Resource Locator (URL for short). For example, you can first obtain the URL of the tile map provided by the electronic map service provider, and then download the tile map as needed Fill the parameters in the URL with the tile map to form a complete URL. For example, the parameters that can be filled can include at least the type of electronic map, latitude and longitude, area span, zoom level, and preferably, can also include label language. After obtaining the complete URL, the tile map to be downloaded can be downloaded according to the complete URL. For obtaining the URL, a packet capture tool can be used to capture the interaction with the electronic map service provider, and the URL can be obtained by analyzing the captured data packets. Of course, for some electronic map service providers with open ports, they may directly provide URLs for downloading tile maps. For latitude and longitude, the global latitude and longitude can be transformed into a plane coordinate system according to the Mercator projection formula; use the coordinates of the plane coordinate system to fill the longitude and latitude parameters in the URL. The origin of the coordinate system can be set as required, for example, you can use the prime meridian and The intersection point of the equator is the origin, and the values of x and y at this time can be positive or negative; in order to make the values of x and y all positive, you can also move the origin of the coordinate system to the upper left corner, and use the ink card When using the projection formula, the length of the earth's radius can be used to calculate the plane coordinate system.

Taking the origin of the coordinate system at the upper left corner as an example, after downloading the tile map locally, you can use various ways to create a directory. In this embodiment, a better way to create a directory is provided: you can use the A multi-level directory is established by at least one of the following: type of electronic map, latitude and longitude, zoom level. The latitude and longitude are expressed as (x, y), and the coordinate system composed of x and y is converted from longitude to the horizontal x-axis of the plane coordinate system according to the Mercator projection formula, and from latitude to the vertical y-axis of the plane coordinate system. When the maximum zoom level of the tile map of the electronic map is n, the value of x is at most 2 ⁿ -1, and the value of y is 2 ⁿ -1.

An optimal implementation manner of creating a directory is selected below for illustration. In the best implementation, each zoom level corresponds to a directory, and the x value of the tile map under the zoom level is divided by M, the quotient is the name of the secondary directory under the zoom level directory, and the remainder is the The third-level directory name under the zoom level directory, divide the y value of the tile map under the zoom level by M, the quotient is the fourth-level directory name under the zoom level directory, and the remainder is the image file of the tile map File name, where M is a positive integer, and M corresponds to the zoom level. Through this embodiment, the number of levels of the directory can be determined by setting the value of M. For example, for zoom level 1, the number of pictures in the directory is much smaller than the number of pictures in the directory of zoom level 10, then for zoom level 1 , the quotient of the division result is 0, that is, the name of the secondary directory is 0. It should be noted that 0 can be used as the name of the secondary directory, or the name of the secondary directory can be omitted, and the secondary directory is no longer set. For zoom level 10, it may be necessary to set a secondary directory, or even a tertiary directory. From which zoom levels need to set the secondary directory, etc. can be controlled by adjusting the M value. When the maximum zoom level is 20, the value of M is 1024, which is more optimal.

Taking the zoom level of the electronic map of the downloaded tile map as the maximum n=20, M=1024 as an example, the storage method of the multi-level directory index is described.

When the maximum zoom level of the electronic map of the tile map to be downloaded is 20, the horizontal maximum index x of the electronic map is 2 ²⁰ -1, and the vertical maximum index y of the electronic map is 2 ²⁰ -1, where x and y The formed coordinate system is to transform the latitude into the horizontal x-axis of the plane coordinate system according to the Mercator projection formula, and convert the longitude into the longitudinal y-axis of the plane coordinate system. Firstly, it is divided into different categories according to the type of electronic map. Secondly, with the zoom level as the first-level category, divide the horizontal maximum index x value of the electronic map by 1024, the quotient is the second-level category name, and the remainder is the third-level category name. Divide the maximum vertical index y value of the electronic map by 1024, the quotient is the name of the fourth-level directory, and the remainder is the file name of the image file of the tile map.

It should be noted that during implementation, the zoom levels of the electronic maps provided by different electronic map providers are not exactly the same. The higher the zoom level, the higher the accuracy of the electronic map. The stored directory level depends on the selected The size of the divisor, for example, when the maximum zoom level of the electronic map is 10, the maximum horizontal index x of the electronic map is 2 ¹⁰ -1, the maximum vertical index y is 2 ¹⁰ -1, after dividing by the maximum horizontal index x of the electronic map Take 1024, the quotient is the name of the second-level directory, and the remainder is the name of the third-level directory. Divide the maximum vertical index y value of the electronic map by 1024, the quotient is the name of the fourth-level directory, and the remainder is the file name of the image file of the tile map , there is only one directory name; if the horizontal maximum index x value of the electronic map is divided by 512, the quotient is the second-level directory name, and the remainder is the third-level directory name, and the vertical maximum index y value of the electronic map is divided by 512, the quotient is The four-level directory name, the remainder is the file name of the image file of the tile map, then there can be three directory names and one folder, or, when the maximum zoom level of the electronic map is 22, the horizontal maximum index x of the electronic map is 2 ²² -1, the maximum vertical index y is 2 ²² -1, after dividing the maximum horizontal index x value of the electronic map by 2048, the quotient is the name of the second-level directory, and the remainder is the name of the third-level directory, and the maximum vertical index y of the electronic map is The value is divided by 2048, the quotient is the name of the fourth-level directory, and the remainder is the file name of the image file of the tile map. It can be seen that there may be different ways to select the divisor in the above calculation, and this embodiment is a preferred one, but is not limited thereto.

As a preferred implementation, in obtaining the tile map locally, organizing and displaying the tile map, the tile number and the pixel coordinates in the tile can be obtained according to the zoom level and latitude and longitude in the query request, and the tile The number is converted to the screen coordinates of the display screen; the number of tiles filling the display screen and the coordinate range of the display screen are obtained according to the block number and the pixel coordinates in the block; the coordinate range is converted into the number of the block, and obtained sequentially according to the number tile map data, and organize and display the obtained tile map, preferably, obtain the tile map data from the memory buffer, if the tile map data cannot be obtained from the memory, then from The local memory loads the data of the tile map, and stores the data of the tile map into the memory buffer.

Through the above embodiment, the tile map of the electronic map is downloaded in advance, and the tile map is stored locally in the form of a multi-level directory index; the query request is received, and the tile map corresponding to the query request is determined; the tile map is obtained from the local , organizes and displays the tile map. This makes it possible to browse the electronic map quickly and in real time when there is no Internet access, thereby improving user experience.

In this embodiment, an electronic map display device is also provided, which is used to realize the above-mentioned embodiment and its preferred implementation mode, which has already been described and will not be repeated, and the modules involved in the system will be described below . It should be noted that the terms "module" and "unit" used below may be a combination of software and/or hardware that implements predetermined functions. Although the systems and methods described in the following embodiments are preferably implemented in software, implementations in hardware or a combination of software and hardware are also possible.

FIG. 2 is a structural block diagram of an electronic map display device according to an embodiment of the present invention. As shown in FIG. 2 , the device includes a download module 20 , a storage module 30 , a query module 40 and a display module 50 . Each module of the device will be described below.

The download module 20 is used to pre-download the tile map of the electronic map; the storage module 30 is connected to the download module 20, and is used to store the tile map locally in the form of a multi-level directory index; the query module 40 is connected to the storage module 30, It is used to receive a query request and determine the tile map corresponding to the query request; the display module 50 is connected to the query module 40 and used to obtain the tile map locally, organize and display the tile map.

FIG. 3 is a structural block diagram of an electronic map display device according to a preferred embodiment of the present invention. As shown in FIG. Each module of the device will be described below, and those that have already been described will not be repeated.

The obtaining unit 200 is used to obtain the URL of the tile map provided by the electronic map service provider; the forming unit 204 is connected to the obtaining unit 200, and is used to fill the parameters in the URL according to the tile map downloaded as required to form a complete URL; the download unit 206 is connected to the trip unit 204, and is used for downloading the tile map to be downloaded according to the complete URL.

The storage module 30 is used to establish a multi-level directory according to at least one of the following: the type of electronic map, latitude and longitude, and zoom level, wherein the latitude and longitude are expressed as (x, y), and the coordinate system formed by x and y is based on the Mercator projection The formula converts the global longitude and latitude into a plane coordinate system, the origin is located in the upper left corner of the coordinate system, converts the longitude into the horizontal x-axis of the coordinate system, and converts the latitude into the vertical y-axis of the plane coordinate system, when the maximum zoom of the tile map of the electronic map When the level is n, the value of x is at most 2 ⁿ -1, and the value of y is 2 ⁿ -1.

FIG. 4 is a structural block diagram of an electronic map display device according to another preferred embodiment of the present invention. As shown in FIG. 4 , in this device, the display module 50 may further include an acquisition unit 500 . The obtaining unit 500 is used to obtain the data of the tile map from the memory buffer, and when the data of the tile map cannot be obtained from the memory, load the data of the tile map from the local memory, and convert the data of the tile map into Data is stored in the memory buffer. Those that have already been described will not be repeated.

A preferred embodiment will be described below in conjunction with the above embodiments and preferred implementation modes. Although this preferred embodiment is described by taking Google Maps as an example, it is also applicable to electronic maps provided by other map providers. Since Google successfully launched Google Maps, the tile map technology has taken a big step forward. Google Maps has used this technology from the initial ordinary map to the current terrain map, satellite map and synthetic map, allowing global coverage The rich map resources can be browsed through the network.

In this preferred embodiment, the tiled map data of the specified area is downloaded, and the data storage is effectively organized, and the display boundary when the map is displayed offline is determined, and the map data is read and cached. In an environment connected to the Internet, the tile map data of Google Maps is obtained in advance, and the tile map data is stored locally. In the offline environment, based on these acquired tile map data, the electronic map can be browsed on the client side, and operations such as panning and zooming can be performed.

In this preferred embodiment, since the tile map data uses Google's map data, the map slice rules and acquisition mechanism of Google Maps are described in this embodiment, and the downloaded data is effectively organized , establish a fast indexing mechanism so that the data can be retrieved quickly when displaying. When browsing the map offline, it is necessary to accurately determine the map boundary and obtain the corresponding tile map. The cache technology will also be used to store the read tile map data into the memory buffer and create an index, which will be able to update the tile map in operations such as translation. Quickly display the map.

Google Maps uses the Web Mercator projection (Spherical Mercator EPSG: 900913 (EPSG: 3857)), which simulates the earth as a sphere, with the entire world as the scope, the equator as the standard parallel, and the prime meridian as the central meridian. The point of intersection is the origin of the coordinates, the east to north is positive, the west to south is negative, the north and south poles are directly below and above the map, and the east-west direction is on the right and left of the map. When slicing Google Maps, take the latitude direction as the x-axis, positive to the right; use the meridian direction as the y-axis, and downwards as positive, and move the origin to the upper left corner, which ensures that the number of the tile map after slicing is in x, All positive values in the y direction are convenient for calculation.

Google Maps mainly provides ordinary maps (also known as flat maps), topographic maps, satellite maps, and composite maps. The map data is all raster data. Referring to the pyramid model and according to different zoom levels, it is cut into 256×256 pixel map tiles in the Portable Network Graphic Format (PNG for short). Google Maps currently provides 23 zoom levels, that is, 0-22, wherein, when the zoom level is 0, the whole world is displayed in one tile.

Fig. 5 is a schematic diagram of the slice distribution of the map when the zoom level is 1 related to the embodiment of the present invention. As shown in Fig. 5, when the zoom level is 1, the whole world is sliced into 4 pictures (for example, when it is a Google map, The whole world map can be sliced into 4 blocks of 256×256 pixel pictures), and the number of each block is as shown in the figure, which is (0, 0) in turn, that is, x=0, y=0 in the upper left; (1, 0), That is, upper right x=1, y=0; (0,1), that is, lower left x=0, y=1; (1,1), that is, lower right x=1, y=1. By analogy, every time the zoom level increases by 1, each small block is sliced into 4 pieces, the number of tiles will be doubled in the horizontal and vertical directions, and the total will be increased by 4 times compared with the previous level. After slicing, they are numbered sequentially from left to right in the direction of the x-axis and from top to bottom in the direction of the y-axis. When the zoom level is 22, when the map is at its finest, the number of tiles will be increased to 2 ^2×22 . The value ranges of x and y are 0 to 2 ²² -1.

Fig. 6 is a flow chart of downloading and storing tile map data according to a preferred embodiment of the present invention. When downloading, the user can use the download program to input the following parameters: the type of electronic map to be downloaded, the latitude and longitude of the electronic map to be downloaded, and the map to be downloaded. The region span, zoom level, preferably, you can also enter the label language, for example, it can be en, which means English, of course, the label language can also not be input, directly download the version in the default language, or according to the local language of the downloader's location Download, for example, in China, the default is Chinese. As shown in Figure 6, the process includes the following steps:

Step S601, acquiring a reference URL, that is, a webpage address. First, according to the type of electronic map, request the following URL: http://maps.google.com/maps? t=? , where, when t is m, it represents a normal map, when t is h, it represents a synthetic map, when t is k, it represents a satellite map, and when t is p, it represents a terrain map.

Analyze the response page and match in sequence according to the following list of regular expressions:

There are many forms of acquisition, for example, the form of acquisition may be http://mt0.google.com/vt/lyrs=m140&, or http://mt0.google.com/vt/v=m140&, or http:/ /khm0.google.com/kh/v=79&, but not limited to. The above list provides the URL format of the map service currently provided by the Google server, and the matching format is the base URL of the current map type.

Step S602, calculating the area number (x, y) according to the latitude and longitude. It should be noted that Google uses the Web Mercator projection, that is, the earth is projected as a sphere with a radius of 6,378,137 meters and the origin at the intersection of the prime meridian and the equator. In addition, the latitude and longitude in the geocentric coordinate system of WGS84 (EPSG: 4326) is adopted. In WGS84 (EPSG: 4326), the longitude is east longitude, and the value range is -180 to 180 degrees; the latitude is north latitude, and the value range is -90 ~90 degrees. Other electronic map providers may adopt other methods, which are not limited thereto.

The user inputs the latitude and longitude in the geocentric coordinate system of WGS84 (EPSG: 4326), and then converts the latitude and longitude into coordinates (x, y) in the plane coordinate system according to the Mercator projection formula, and the unit is meters, and then takes this as the center according to the input The area span of the region is reversely calculated to the latitude and longitude in the WGS84 coordinate system of the upper left corner and the lower right corner when projected onto the plane, and the calculated latitude and longitude are the boundary latitude and longitude.

It should be noted that when Google numbers the tile map x and y according to the direction of longitude and latitude, the origin of the coordinates is moved to the point O in Figure 5, and the coordinates need to be transformed in the formula, and then the numbering rules of Google Maps are followed. , calculate the x and y numbers of the boundary latitude and longitude, and the range of x and y is the range of the area number. It should be noted that during the implementation, since the web Mercator projection is a square, the actual latitude range is -85.051128 to 85.051128 degrees through the calculation of the Mercator curve, so when the latitude φ is close to the poles, the map will have serious problems. Deformation, therefore, Google does not provide high-resolution maps of high latitudes for the time being.

The integer part of the calculated x and y values is the tile coordinate in the Google map coordinates when the latitude and longitude are (λ, φ), and the fractional part is calculated according to the 256×256 pixels of each tile in the Google map, and the The offset of the point in the coordinates of this tile. This formula will also be used when displaying the map.

Step S603, organize the complete URL, and obtain the tile map data through multiple threads. After obtaining the range of x and y numbers of the boundary, it is spliced together with the base URL, label language, and zoom level into a form: base URL&hl=? &x=? &y=? &z=? The complete URL of , where the label language hl can be en, which means English, zh, which means Chinese, jp, which means Japanese, etc., and z is the zoom level.

Google adopts load balancing and divides the servers storing map data into 4 sets, namely mt0, mt1, mt2, and mt3. The data on the 4 servers are exactly the same. Satellite map data is separately provided by 4 servers for storage, namely khm0, khm1, khm2, and khm3. And Google will take restrictions on too much concurrent acquisition of map data, and when too much data is requested, an error page will be returned. Therefore, multi-threading technology is used to circularly request the generated complete URL to different servers to obtain the required tile map data.

Step S604, establishing a multi-level directory index mechanism to store tile map data. After the data is obtained, it is stored locally in the form of a multi-level directory index, which is convenient for quickly indexing the data when displaying. In order to achieve a balance between map resolution and data management, in this preferred embodiment, the maximum zoom level of the map is selected as 20, the maximum index of the horizontal coordinate x is 2 ²⁰ −1, and the maximum index of the vertical coordinate y is also 2 ²⁰ − 1.

In this preferred embodiment, the maximum zoom level of the map is 20, the maximum index of the horizontal coordinate x is 2 ²⁰ -1, and the maximum index of the vertical coordinate y is 2 ²⁰ -1 as an example to illustrate the locally saved tile map.

Fig. 7 is a schematic diagram of the tile map data organization structure according to a preferred embodiment of the present invention, as shown in Fig. 7: firstly divide different catalogs according to map type (for example, common map, topographic map is divided into two different catalogs), secondly with The zoom level is a directory (for example, when the zoom level is 9, the stored directory name is 9), under this zoom level directory, divide the x value by 1024, the quotient is the second-level directory name, and the remainder is the third-level directory name , the two levels of directories can contain a total of 1024×1024 directories, which can fully accommodate the maximum index 2 ²⁰ -1 when the level is 20. Similarly, divide the value of y by 1024, the quotient is the name of the fourth-level directory, and the remainder is the PNG file The file name can hold 1024 folders, and each folder can hold 1024 PNG files.

Figure 8 is a flow chart of offline display of Google Maps according to a preferred embodiment of the present invention. When browsing maps offline, the user inputs the latitude and longitude of the desired electronic map in the system, and the system will display the map at the center of the browsing window centered on the latitude and longitude. point, the surrounding area determined according to the span of the area will fill the entire window, and operations such as browsing, zooming, and panning can be performed on the map. As shown in Figure 8, the process includes the following steps:

Step S801, obtain corresponding tile map block coordinates and offset pixel positions according to user input, and convert them into screen coordinates. In this step S801, the screen coordinate system is determined with the browsing window as the scope, the x-axis is the horizontal direction, the y-axis is the vertical direction, and the center point of the browsing window is the origin. Calculate the block number (x, y) and pixel coordinates in the block according to the zoom level and latitude and longitude input by the user, and transform the block coordinates into screen coordinates.

Step S802, taking the tile in step S801 as the center, and determining the boundary to be displayed according to the size of the browsing window. Wherein, the coordinates of the block and the pixel coordinates in the block calculated in step S801 are taken as the center of the browsing window, and the number of tiles and the range of screen coordinates required to fill the browsing window are calculated.

Step S803, querying the buffer, acquiring and splicing tile maps. Transform the screen coordinate range calculated in step S802 into a tile number (x, y), and then sequentially acquire tile map data and stitch pictures in the browsing window.

When obtaining data, it is necessary to judge whether the tile map data is the first time to load the tile map data. The method of judging can be to use the full path of the image to be queried as the index to query the buffer. If the query cannot be found, load the tile map from the local storage system Data, when loading, calculate the file path of the actual tile map according to the tile number (x, y) and the data organization method when storing the tile map data (for example, the method shown in Figure 7 can be used), and then load the map data , and put it into the buffer with the full path of the image as the index; if it can be queried, directly load the tile map data from the buffer.

Step S804, refreshing the displayed page when changing the coordinates or zooming or panning the map. When the browsing window changes or the map is panned or zoomed, the image needs to be refreshed. At this time, the screen coordinates and block numbers of the image to be loaded need to be recalculated, and then the full path of the image is calculated, and then searched in the buffer. If not found , you can find the tile map stored locally again, and if it can be found, load it directly. The buffer storage is used here, and the data is directly read from the memory, which effectively solves the frequent access to the local storage file when the image is repeatedly panned, and can also greatly reduce the delay.

Through the above-mentioned embodiment and its preferred implementation mode, the tile map data is separated from the use of electronic map services, and the required tile map data of the electronic map is downloaded in advance when there is Internet access, and Internet access is not required during use, because The tile map data is pre-downloaded and only needs to be downloaded once. The client directly obtains the data from the local when browsing, so that the browsing speed is extremely fast, and the map can be displayed in real time, which improves the user experience.

In another embodiment, software is also provided, and the software is used to implement the technical solutions described in the above embodiments and preferred embodiments.

In another embodiment, there is also provided a storage medium in which the above software is stored, and the storage medium includes but not limited to an optical disk, a floppy disk, a hard disk, a rewritable memory, and the like.

Obviously, those skilled in the art should understand that each module or each step of the above-mentioned present invention can be realized by a general-purpose computing device, and they can be concentrated on a single computing device, or distributed in a network formed by multiple computing devices Optionally, they can be implemented with program codes executable by computing devices, so that they can be stored in storage devices and executed by computing devices, or they can be made into individual integrated circuit modules, or their Multiple modules or steps are implemented as a single integrated circuit module. As such, the present invention is not limited to any specific combination of hardware and software.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (11)

1. A method for displaying an electronic map, comprising the steps of: downloading the tile map of the electronic map in advance, and storing the tile map locally in a multi-level directory; receiving a query request, and determining a tile map corresponding to the query request; Obtain the tile map locally, organize and display the tile map. 2. The method according to claim 1, wherein downloading the tile map of the electronic map in advance comprises: Obtain the uniform resource locator of the tile map provided by the electronic map service provider; Filling the parameters in the uniform resource locator according to the tile map to be downloaded to form a complete uniform resource locator; Downloading the tile map to be downloaded according to the complete uniform resource locator. 3. The method according to claim 2, wherein filling the latitude and longitude in the uniform resource locator according to the tile map to be downloaded comprises: Convert global latitude and longitude to a plane coordinate system using the length of the earth's radius according to the Mercator projection formula; The latitude and longitude parameters in the uniform resource locator are filled with the coordinates of the plane coordinate system. 4. The method according to claim 1, wherein the manner of the multi-level directory index comprises: The multi-level directory is established according to at least one of the following: the type of the electronic map, the latitude and longitude, and the zoom level, wherein the latitude and longitude are expressed as (x, y), and the coordinate system composed of x and y is based on the Mercator projection The formula converts longitude into a plane coordinate system, the origin is located in the upper left corner of the plane coordinate system, converts longitude into the horizontal x-axis of the plane coordinate system, and converts latitude into the vertical y-axis of the plane coordinate system, when the When the maximum zoom level of the tile map of the electronic map is n, the value of x is at most 2 ⁿ -1, and the value of y is 2 ⁿ -1 at most. 5. The method according to claim 4, wherein the manner of the multi-level directory index further comprises: Each zoom level corresponds to a directory, divide the x value of the tile map under the zoom level by M, the quotient is the name of the second-level directory under the zoom level directory, and the remainder is the name of the third-level directory under the zoom level directory , dividing the y value of the tile map under the zoom level by M, the quotient is the fourth-level directory name under the zoom level directory, and the remainder is the file name of the image file of the tile map, wherein the M is A positive integer, the M corresponds to the zoom level. 6. The method according to claim 5, wherein the M values corresponding to all zoom levels are 1024. 7. The method according to any one of claims 4 to 6, wherein determining the tile map corresponding to the query request, obtaining the tile map locally, organizing and displaying the tile map includes : According to the zoom level and latitude and longitude in the query request, determine (x, y) of the tile map and pixel coordinates in the tile map, and convert the pixel coordinates into screen coordinates of the display screen; determining the number of tiles filling the display screen and the coordinate range of the display screen; Acquire the tile map locally according to (x, y) of the tile map, organize and display the obtained tile map. 8. The method according to claim 1, wherein obtaining the tile map locally, organizing and displaying the tile map further comprises: Acquire the data of the tile map from the memory buffer, if the data of the tile map cannot be obtained from the memory, load the data of the tile map from the local memory, and store the tile The data of the map is stored in the memory buffer. 9. A display device for an electronic map, characterized in that it comprises: The download module is used to pre-download the tile map of the electronic map; A storage module, configured to store the tile map locally in the form of a multi-level directory index; A query module, configured to receive a query request and determine a tile map corresponding to the query request; The display module is configured to obtain the tile map locally, organize and display the tile map. 10. The device according to claim 9, wherein the download module comprises: The obtaining unit is used to obtain the uniform resource locator of the tile map provided by the electronic map service provider; A forming unit, configured to fill parameters in the uniform resource locator according to the tile map to be downloaded to form a complete uniform resource locator; A downloading unit, configured to download the tile map to be downloaded according to the complete uniform resource locator. 11. The device according to claim 9 or 10, wherein the storage module is used to establish the multi-level directory according to at least one of the following: the type, latitude and longitude, and zoom level of the electronic map, wherein the The latitude and longitude are expressed as (x, y), and the coordinate system formed by x and y is a coordinate system converted according to the Mercator projection formula. The x-axis converts the latitude into the longitudinal y-axis of the plane coordinate system. When the maximum zoom level of the tile map of the electronic map is n, the value of x is at most 2 ⁿ -1, and the value of y The value is ²ⁿ -1.

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