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Area Measurement Example

This example demonstrates how to perform area measurement using the DMap3D SDK.

Preview​

The user can click on the map to draw a polygon, double-click to finish drawing, and display the area.

Complete Code​

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

interface MeasurementResult {
  area: number
  perimeter: number
}

function AreaMeasurement() {
  const containerRef = useRef<HTMLDivElement>(null)
  const viewerRef = useRef<Cesium.Viewer | null>(null)
  const toolRef = useRef<any>(null)
  const [result, setResult] = useState<MeasurementResult | null>(null)
  const [isMeasuring, setIsMeasuring] = useState(false)

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

    // Create Viewer
    const viewer = new Cesium.Viewer(containerRef.current, {
      terrain: Cesium.Terrain.fromWorldTerrain(),
      timeline: false,
      animation: false,
      baseLayerPicker: false,
    })
    viewerRef.current = viewer

    // Fly to Beijing
    viewer.camera.flyTo({
      destination: Cesium.Cartesian3.fromDegrees(116.3912757, 39.906217, 10000),
    })

    // Create measurement tool
    const tool = new DMap3D.measurement.area(viewer, {
      fillColor: Cesium.Color.BLUE.withAlpha(0.3),
      outlineColor: Cesium.Color.BLUE,
      outlineWidth: 3,
      showLabel: true,
      clampToGround: true,
    })
    toolRef.current = tool

    // Listen for measurement start
    tool.on('measureStart', () => {
      setIsMeasuring(true)
      setResult(null)
    })

    // Listen for measurement update
    tool.on('measureUpdate', (data: MeasurementResult) => {
      setResult(data)
    })

    // Listen for measurement completion
    tool.on('measureComplete', (data: MeasurementResult) => {
      setIsMeasuring(false)
      setResult(data)
    })

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

  const handleStart = () => {
    toolRef.current?.start()
  }

  const handleClear = () => {
    toolRef.current?.clear()
    setResult(null)
    setIsMeasuring(false)
  }

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

      {/* Control Panel */}
      <div className="control-panel">
        <h3>Area Measurement</h3>
        <p>Click on the map to draw a polygon, double-click to finish</p>

        <div className="buttons">
          <button onClick={handleStart} disabled={isMeasuring}>
            {isMeasuring ? 'Measuring...' : 'Start Measurement'}
          </button>
          <button onClick={handleClear}>Clear</button>
        </div>

        {/* Display results */}
        {result && (
          <div className="result">
            <h4>Measurement Result</h4>
            <p>Area: {result.area.toFixed(2)} sq m</p>
            <p>Area: {(result.area / 10000).toFixed(4)} hectares</p>
            <p>Perimeter: {result.perimeter.toFixed(2)} m</p>
          </div>
        )}
      </div>
    </div>
  )
}

export default AreaMeasurement

Stylesheet​

src/components/AreaMeasurement.css
.area-measurement {
  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: 10px;
  margin-bottom: 15px;
}

.buttons button {
  flex: 1;
  padding: 8px 16px;
  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;
}

.result {
  border-top: 1px solid #e8e8e8;
  padding-top: 15px;
}

.result h4 {
  margin: 0 0 10px 0;
  font-size: 16px;
}

.result p {
  margin: 5px 0;
  font-size: 14px;
  color: #333;
}

Key Code Explanation​

1. Create Viewer​

const viewer = new Cesium.Viewer(containerRef.current, {
  terrain: Cesium.Terrain.fromWorldTerrain(), // Use world terrain
  timeline: false,  // Hide timeline
  animation: false, // Hide animation widget
  baseLayerPicker: false, // Hide base layer picker
})

2. Create Measurement Tool​

const tool = new DMap3D.measurement.area(viewer, {
  fillColor: Cesium.Color.BLUE.withAlpha(0.3), // Semi-transparent blue fill
  outlineColor: Cesium.Color.BLUE,              // Blue outline
  outlineWidth: 3,                               // Outline width
  showLabel: true,                               // Show label
  clampToGround: true,                           // Clamp to ground
})

3. Listen for Events​

// Measurement start
tool.on('measureStart', () => {
  setIsMeasuring(true)
})

// Measurement update (real-time display)
tool.on('measureUpdate', (data) => {
  setResult(data)
})

// Measurement complete
tool.on('measureComplete', (data) => {
  setIsMeasuring(false)
  setResult(data)
})

Extended Features​

You can add the following features based on this example:

  1. Unit Switching - Support square meters, hectares, square kilometers, and other units
  2. Data Export - Export measurement results as JSON or CSV
  3. History - Save multiple measurement results
  4. Style Customization - Let users customize colors and styles