How to convert Baidu map coordinates in Javascript

In web applications, it is often necessary to use Javascript to convert the latitude and longitude coordinates of a location to achieve more complete map services or other functions. As one of the most widely used map APIs in China, Baidu Maps allows developers to use Javascript to call its API to achieve operations such as coordinate conversion. This article will introduce in detail the method and application of Javascript Baidu map coordinate conversion.

1. Basic concepts

Before performing Javascript Baidu map coordinate conversion, you need to understand some basic concepts in order to better understand the subsequent content of this article.

1. Map coordinate system

The map coordinate system is a mathematical model used to describe the position of each point on the earth's surface. Its methods include longitude and latitude coordinate systems, projected coordinate systems, and Gaussian coordinate systems. -Krüger coordinate system, etc. In Baidu Maps, the latitude and longitude coordinate system is used.

2. Latitude and longitude coordinate system

The latitude and longitude coordinate system is a coordinate system used to describe the position of points on the earth. Among them, longitude refers to the angle between a point on the earth's surface and the prime meridian, ranging from 0 degrees east longitude to 180 degrees west longitude; latitude refers to the angle between a point on the earth's surface and the equator, ranging from Between 0 degrees south latitude and 90 degrees north latitude. The coordinates composed of longitude and latitude are the longitude and latitude coordinates.

3. Coordinate transformation

Coordinate transformation is the process of converting coordinates in one coordinate system to coordinates in another coordinate system. In Javascript Baidu Map, common coordinate conversion methods include the mutual conversion of latitude and longitude coordinates and Baidu Map coordinates.

2. Coordinate conversion method

There are many methods to choose from for coordinate conversion in Javascript Baidu Map, which will be introduced one by one below.

1. Baidu Map API conversion method

The first introduction is to use Baidu Map API to perform coordinate conversion. The specific steps are as follows:

a. Introduce the Baidu Map API file into the page:

<script></script>

The "your key" here needs to be replaced by the developer you applied for on the Baidu Map Open Platform key.

b. Use the converter object of the API for coordinate conversion

First you need to instantiate a converter object:

var convertor = new BMap.Convertor();

Then use the converter object's translate method to perform coordinate conversion. For example, convert the coordinates of longitude 120 and latitude 40 into Baidu map coordinates:

var point = new BMap.Point(120, 40);

var translateCallback = function (data) {
  if (data.status === 0) {
    var baiduPoint = data.points[0];
    console.log(baiduPoint.lng + ", " + baiduPoint.lat);
  }
};

convertor.translate([point], 1, 5, translateCallback);

Among them, the translate method accepts three parameters:

• points: the coordinate array to be converted, Each coordinate is a BMap.Point object.
• from: Original coordinate system type, 0 indicates the system default coordinate type, such as Mars coordinates, Google coordinates, etc.; 1 indicates WGS84 coordinate system; 3 indicates Baidu coordinate system.
• to: Target coordinate system type, the same as the from parameter.
• callback: callback function after successful conversion, accepts an object parameter data, where data.status represents the conversion status, 0 represents success, non-0 represents failure; the data.points array contains the converted coordinate points.

2. Online coordinate conversion website

In addition to using Baidu Map API, you can also use some online coordinate conversion websites. The most commonly used ones include:

• Coordinate Conversion Assistant
• Mars Coordinate Converter
• Various map API coordinate conversion tools

Use The coordinate conversion methods of these websites are similar, and the specific steps can be viewed on the website.

3. Source code conversion method

If the above two methods cannot meet the needs, you can also use the third method, which is to find the relevant longitude and latitude to convert to Baidu map coordinates Javascript source code to call.

Of course, since Baidu Map API is very mature and the stability of many third-party online coordinate conversion websites has been ensured, this article will not introduce the specific operation of the third method in detail.

3. Application examples

Finally, this article will demonstrate an example of using coordinate conversion in Javascript Baidu Map.

Suppose we need to mark our location on the map, but we have no way to obtain our own Baidu map coordinates, only the longitude and latitude. At this time, we can use the Javascript Baidu map coordinate conversion method to convert our longitude and latitude coordinates into Baidu map coordinates, and then mark them on the map.

The following is the complete code implementation:

nbsp;html>


  
  
  <script></script>
  


  

  <script>
    var map = new BMap.Map("map");
    var point = new BMap.Point(116.404, 39.915);
    map.centerAndZoom(point, 15);

    var convertor = new BMap.Convertor();
    var translateCallback = function (data) {
      if (data.status === 0) {
        var baiduPoint = data.points[0];
        var marker = new BMap.Marker(baiduPoint);
        map.addOverlay(marker);
      }
    };
    convertor.translate([point], 1, 5, translateCallback);
  </script>

In the above example, first create a BMap.Map object and specify a coordinate point with latitude and longitude of 116.404 and 39.915 as the center point of the map. Then use the converter object to convert the point from latitude and longitude coordinates to Baidu map coordinates, and mark it on the map.

4. Summary

This article mainly introduces the method and application of Javascript Baidu map coordinate conversion. By using Baidu Map API, online coordinate conversion website or source code conversion, coordinate system conversion and application can be easily realized. In actual projects, when you need to mark a location on a map or implement other similar functions, you can consider using Javascript Baidu map coordinate conversion technology to improve the usability and user experience of the application.

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