Skip to main content

Polygon Drawing Example

This example demonstrates how to interactively draw polygons on the map using the DMap3D SDK.

Preview​

The user left-clicks to add vertices in sequence, and right-clicks to finish drawing. The polygon is automatically closed, with support for fill and outline styles.

Complete Code​

src/components/PolygonDrawing.tsx
import { useEffect, useRef, useState } from 'react'
import * as Cesium from 'cesium'
import DMap3D from 'dmap3d'
import './PolygonDrawing.css'

function PolygonDrawing() {
  const containerRef = useRef<HTMLDivElement>(null)
  const viewerRef = useRef<Cesium.Viewer | null>(null)
  const toolRef = useRef<any>(null)
  const [isActive, setIsActive] = useState(false)

  useEffect(() => {
    if (!containerRef.current) return

    Cesium.Ion.defaultAccessToken = 'your-cesium-ion-token'

    const viewer = new Cesium.Viewer(containerRef.current, {
      animation: false,
      fullscreenButton: false,
      geocoder: false,
      homeButton: false,
      sceneModePicker: false,
      selectionIndicator: false,
      timeline: false,
      navigationHelpButton: false,
      infoBox: false,
      baseLayerPicker: false,
      terrainProvider: new Cesium.EllipsoidTerrainProvider({}),
    })
    viewerRef.current = viewer

    viewer.camera.setView({
      destination: Cesium.Cartesian3.fromDegrees(116.4074, 39.9042, 5000),
      orientation: {
        heading: Cesium.Math.toRadians(0),
        pitch: Cesium.Math.toRadians(-45),
        roll: 0,
      },
    })

    // Create polygon drawing tool
    const tool = new DMap3D.drawing.polygon({
      viewer,
      style: {
        fillColor: '#0000FF',
        fillAlpha: 0.3,
        outlineColor: '#FFFFFF',
        outlineWidth: 2,
        outlineAlpha: 1.0,
      },
      clampToGround: true,
    })
    toolRef.current = tool

    return () => {
      tool.destroy()
      viewer.destroy()
    }
  }, [])

  const handleDraw = () => {
    const tool = toolRef.current
    if (!tool) return
    tool.draw((entity: any, positions: Cesium.Cartesian3[]) => {
      console.log('Polygon drawing complete, vertex count:', positions.length)
      setIsActive(false)
    })
    setIsActive(true)
  }

  const handleStop = () => {
    toolRef.current?.deactivate()
    setIsActive(false)
  }

  const handleClear = () => {
    toolRef.current?.clear()
    if (isActive) toolRef.current?.deactivate()
    setIsActive(false)
  }

  // Load from data
  const handleLoadData = () => {
    const tool = toolRef.current
    if (!tool) return
    tool.loadFromData([
      [116.39, 39.90],
      [116.41, 39.90],
      [116.41, 39.92],
      [116.39, 39.92],
    ])
  }

  return (
    <div className="polygon-drawing">
      <div ref={containerRef} className="cesium-container" />

      <div className="control-panel">
        <h3>Polygon Drawing</h3>
        <p>Left-click to add vertices, right-click to finish (auto-close)</p>

        <div className="buttons">
          <button onClick={handleDraw} disabled={isActive}>
            {isActive ? 'Drawing...' : 'Start Drawing'}
          </button>
          <button onClick={handleStop} disabled={!isActive}>Stop</button>
          <button onClick={handleClear}>Clear</button>
        </div>

        <button className="load-btn" onClick={handleLoadData}>
          Load Sample Polygon from Data
        </button>
      </div>
    </div>
  )
}

export default PolygonDrawing

Stylesheet​

src/components/PolygonDrawing.css
.polygon-drawing {
  position: relative;
  width: 100%;
  height: 100vh;
}

.cesium-container { width: 100%; height: 100%; }

.control-panel {
  position: absolute; top: 20px; right: 20px;
  background: rgba(255, 255, 255, 0.95); padding: 20px;
  border-radius: 8px; box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  min-width: 250px;
}

.control-panel h3 { margin: 0 0 10px 0; font-size: 18px; }
.control-panel p { margin: 0 0 15px 0; color: #666; font-size: 14px; }
.buttons { display: flex; gap: 8px; margin-bottom: 15px; }
.buttons button {
  flex: 1; padding: 8px 12px; border: none; border-radius: 4px;
  background: #1890ff; color: white; cursor: pointer; font-size: 14px;
}
.buttons button:hover { background: #40a9ff; }
.buttons button:disabled { background: #d9d9d9; cursor: not-allowed; }

.load-btn {
  width: 100%; padding: 8px; border: 1px solid #1890ff; border-radius: 4px;
  background: white; color: #1890ff; cursor: pointer; font-size: 14px;
}
.load-btn:hover { background: #e6f7ff; }

Key Code Explanation​

1. Create Polygon Drawing Tool​

const tool = new DMap3D.drawing.polygon({
  viewer,
  style: {
    fillColor: '#0000FF',     // Fill color
    fillAlpha: 0.3,           // Fill opacity
    outlineColor: '#FFFFFF',  // Outline color
    outlineWidth: 2,          // Outline width
    outlineAlpha: 1.0,        // Outline opacity
  },
  clampToGround: true,        // Clamp to ground
})

2. Interactive Drawing​

tool.draw((entity, positions) => {
  // entity: Polygon Entity
  // positions: Vertex coordinate array
  console.log('Vertex count:', positions.length)
})

Left-click to add vertices, right-click to finish drawing and auto-close the polygon.

3. Load from Data​

// Longitude-latitude array
tool.loadFromData([
  [116.39, 39.90],
  [116.41, 39.90],
  [116.41, 39.92],
  [116.39, 39.92],
])

Extended Features​

  1. Area Calculation - Automatically calculate polygon area
  2. Vertex Editing - Drag to modify vertices of drawn polygons
  3. Holes - Cut holes inside polygons
  4. Boolean Operations - Polygon union, clipping, and intersection