在做地圖應用時，有時需要根據指定的坐標來畫一個圓形區域，比如簽到打卡類的應用，此時我們可以使用 leaflet.Circle 來在在指定坐標上創建一個圓并添加到的地圖上，其中可以通過 radius 屬性可以指定區域半徑，比如:

const circle = leaflet.circle([lat, lng], {color: 'red',fillColor: 'red',fillOpacity: 0.5,radius: 100,
}).addTo(this.map);

完整例子如下

import { Component, OnInit, AfterViewInit } from "@angular/core";
import * as leaflet from "leaflet";@Component({selector: "app-map-circle",templateUrl: "./map-circle.component.html",styleUrls: ["./map-circle.component.css"],
})
export class MapCircleComponent implements OnInit, AfterViewInit {map!: leaflet.Map;constructor() {}ngOnInit(): void {}ngAfterViewInit(): void {this.initMap();}private initMap(): void {this.map = leaflet.map("map").setView([51.5, -0.09], 16);const tiles = leaflet.tileLayer("https://tile.openstreetmap.org/{z}/{x}/{y}.png", {maxZoom: 19,attribution: '&copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a>',});tiles.addTo(this.map);let marker: leaflet.Marker | null = null;let circle: leaflet.Circle | null = null;this.map.on("click", (e) => {console.log(e.latlng);if (marker) {this.map.removeLayer(marker);}const icon = leaflet.icon({iconUrl: "media/marker-icon.png",iconSize: [25, 41],iconAnchor: [12, 41]});marker = leaflet.marker([e.latlng.lat, e.latlng.lng], {icon: icon}).addTo(this.map);if (circle) {this.map.removeLayer(circle);}circle = this.createCircle(e.latlng.lat, e.latlng.lng, "red").addTo(this.map);});}private createCircle(lat: number, lng: number, color: string): leaflet.Circle {return leaflet.circle([lat, lng], {color: color,fillColor: color,fillOpacity: 0.5,radius: 100,});}
}