How to implement map zoom and drag functions using Python and Baidu Map API

How to use Python and Baidu Map API to implement map zoom and drag functions

Map is one of the most important tools in modern society. It can display geographical location, streets, traffic conditions and other information. In web applications, we often need to integrate maps so that users can view the required location information. Two of the important functions are map zooming and dragging. This article will use Python and Baidu Map API to implement these two functions and provide corresponding code examples.

1. Baidu Map API Introduction
   Baidu Map API is a set of Web service APIs provided by Baidu Company, which can be used to embed Baidu Map services in your own website or application. By using Baidu Map API, developers can implement a series of map-related functions including map display, location search, route planning, etc.
2. Preparation
   Before we start writing code, we need to make some preparations. First, we need to apply for a developer account on the Baidu Developer Platform and create a new application. Then, we can obtain an API key, which will be used to send requests to the Baidu Map API.
3. Install the necessary libraries
   In order to use Python code to access the Baidu Map API, we need to install the corresponding libraries. Among them, the requests library can help us send HTTP requests, and the json library is used to process JSON data returned from the API. Both libraries can be installed using the following command:

pip install requests
pip install json

4. Get the map
   Next, we will write the code to get the map. First, we need to import the required libraries:

import requests
import json

Then, we can define a function to get the map and specify the center point and zoom level of the map:

def get_map(center, zoom):
    url = "http://api.map.baidu.com/staticimage/v2"
    params = {
        "ak": "your_api_key",
        "center": center,
        "zoom": zoom,
        "width": 400,
        "height": 300
    }
    response = requests.get(url, params=params)
    result = json.loads(response.text)
    map_url = result["map_url"]
    return map_url

In the above In the code, we use Baidu Map Static Map API to obtain the map. It should be noted that we need to replace "your_api_key" with the API key you applied for on the Baidu Developer Platform.

5. Zoom the map
   Next, we will write code to implement the zoom function of the map. First, we need to import the necessary libraries and define constants:

import pygame
import requests
import json

WIDTH, HEIGHT = 800, 600
CENTER = "116.404269,39.915173"
ZOOM_LEVEL = 12

Then, we can create a class called "Map" which contains some methods needed to zoom the map:

class Map:
    def __init__(self):
        self.center = CENTER
        self.zoom = ZOOM_LEVEL
        self.map_url = self.get_map_url()

    def get_map_url(self):
        url = "http://api.map.baidu.com/staticimage/v2"
        params = {
            "ak": "your_api_key",
            "center": self.center,
            "zoom": self.zoom,
            "width": WIDTH,
            "height": HEIGHT
        }
        response = requests.get(url, params=params)
        result = json.loads(response.text)
        map_url = result["map_url"]
        return map_url

    def zoom_in(self):
        self.zoom += 1
        self.map_url = self.get_map_url()

    def zoom_out(self):
        self.zoom -= 1
        self.map_url = self.get_map_url()

    def draw(self, screen):
        image = pygame.image.load(requests.get(self.map_url, stream=True).raw)
        screen.blit(image, (0, 0))

In the above code, we define a "Map" class, which contains methods for obtaining the map URL, zooming in and out of the map. When zooming in or out of the map, we just need to increase or decrease the zoom level by 1 and re-fetch the map URL.

6. Drag and Drop Map
   Finally, we will write code to implement the drag and drop function of the map. Similarly, we need to import the necessary libraries and define constants:

import pygame
import requests
import json

WIDTH, HEIGHT = 800, 600
CENTER = "116.404269,39.915173"
ZOOM_LEVEL = 12

Then, we can modify the previous "Map" class to add the function of dragging the map:

class Map:
    def __init__(self):
        self.center = CENTER
        self.zoom = ZOOM_LEVEL
        self.map_url = self.get_map_url()
        self.dragging = False
        self.drag_start_pos = None

    def get_map_url(self):
        url = "http://api.map.baidu.com/staticimage/v2"
        params = {
            "ak": "your_api_key",
            "center": self.center,
            "zoom": self.zoom,
            "width": WIDTH,
            "height": HEIGHT
        }
        response = requests.get(url, params=params)
        result = json.loads(response.text)
        map_url = result["map_url"]
        return map_url

    def zoom_in(self):
        self.zoom += 1
        self.map_url = self.get_map_url()

    def zoom_out(self):
        self.zoom -= 1
        self.map_url = self.get_map_url()

    def start_dragging(self, pos):
        self.dragging = True
        self.drag_start_pos = pos

    def stop_dragging(self):
        self.dragging = False
        self.drag_start_pos = None

    def drag_map(self, pos):
        if self.dragging:
            dx = pos[0] - self.drag_start_pos[0]
            dy = pos[1] - self.drag_start_pos[1]
            lat, lng = map(float, self.center.split(","))
            lat += dy * 0.0001
            lng += dx * 0.0001
            self.center = f"{lng},{lat}"
            self.map_url = self.get_map_url()
            self.drag_start_pos = pos

    def draw(self, screen):
        image = pygame.image.load(requests.get(self.map_url, stream=True).raw)
        screen.blit(image, (0, 0))

In the above code, we added three methods: "start_dragging()", "stop_dragging()" and "drag_map()" to handle mouse press, release and drag events. When dragging the map, we adjust the position of the center point of the map based on the movement distance of the mouse.

7. Use pygame to display the map
   Finally, we use pygame to display the map and implement the interactive functions of zooming and dragging:

import pygame

WIDTH, HEIGHT = 800, 600

pygame.init()
screen = pygame.display.set_mode((WIDTH, HEIGHT))
clock = pygame.time.Clock()

map = Map()

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.MOUSEBUTTONDOWN and event.button == 4:
            map.zoom_in()
        elif event.type == pygame.MOUSEBUTTONDOWN and event.button == 5:
            map.zoom_out()
        elif event.type == pygame.MOUSEBUTTONDOWN and event.button == 1:
            map.start_dragging(event.pos)
        elif event.type == pygame.MOUSEBUTTONUP and event.button == 1:
            map.stop_dragging()
        elif event.type == pygame.MOUSEMOTION:
            map.drag_map(event.pos)

    screen.fill((255, 255, 255))
    map.draw(screen)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()

In the above code, We use pygame to create a window and display the map in the window. We listen to mouse wheel events to implement zooming the map, and listen to mouse left button events to implement dragging the map.

Summary
This article introduces the method of using Python and Baidu Map API to implement map zoom and drag functions, and provides corresponding code examples. Through these examples, you can easily integrate map functions into your own Web applications. Of course, Baidu Map API also provides many other powerful functions, and interested readers can further explore and learn.

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