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Slope Measurement Example

This example demonstrates how to perform two-point slope measurement using the DMap3D SDK, displaying both degrees and percentage.

Preview​

The user clicks two points, and the system automatically calculates the slope between them, displayed in both degrees and percentage.

Complete Code​

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

function SlopeMeasurement() {
  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,
      terrain: Cesium.Terrain.fromWorldTerrain(),
    })
    viewerRef.current = viewer

    // Fly to an area with terrain relief
    viewer.camera.flyTo({
      destination: Cesium.Cartesian3.fromDegrees(86.925, 27.988, 15000),
      orientation: {
        heading: Cesium.Math.toRadians(0),
        pitch: Cesium.Math.toRadians(-45),
        roll: 0,
      },
    })

    // Create slope measurement tool
    const tool = new DMap3D.measurement.slope(viewer)
    tool.updateConfig({
      pointColor: '#ff0000',
      lineColor: '#00ff00',
      fontColor: '#ffffff',
      fontSize: 16,
    })
    toolRef.current = tool

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

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

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

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

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

      <div className="control-panel">
        <h3>Slope Measurement</h3>
        <p>Click two points at different elevations to measure slope</p>

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

        <div className="info">
          <h4>Slope Representations</h4>
          <table>
            <thead>
              <tr><th>Representation</th><th>Description</th></tr>
            </thead>
            <tbody>
              <tr><td>Degrees (deg)</td><td>Angle with the horizontal plane</td></tr>
              <tr><td>Percentage (%)</td><td>Vertical distance / Horizontal distance x 100</td></tr>
            </tbody>
          </table>
        </div>
      </div>
    </div>
  )
}

export default SlopeMeasurement

Stylesheet​

src/components/SlopeMeasurement.css
.slope-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: 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; }

.info { border-top: 1px solid #e8e8e8; padding-top: 15px; }
.info h4 { margin: 0 0 8px 0; font-size: 14px; color: #666; }
.info table { width: 100%; border-collapse: collapse; font-size: 13px; }
.info th, .info td { padding: 6px 8px; border: 1px solid #e8e8e8; text-align: left; }
.info th { background: #fafafa; color: #666; }

Key Code Explanation​

1. Create Slope Measurement Tool​

const tool = new DMap3D.measurement.slope(viewer)

Slope measurement is calculated based on the ENU (East-North-Up) coordinate system, with results displayed in both degrees and percentage.

2. Slope Calculation Principle​

Measuring the slope between two points:

  • Degrees: arctan(height difference / horizontal distance)
  • Percentage: (height difference / horizontal distance) x 100%

For example, 45 deg corresponds to 100%, and 30 deg corresponds to approximately 57.7%.

3. Applicable Scenarios​

Recommended for use in areas with terrain relief. Load global terrain:

const viewer = new Cesium.Viewer(container, {
  terrain: Cesium.Terrain.fromWorldTerrain(),
})

Extended Features​

  1. Slope Classification - Color-code display by slope grade
  2. Path Slope - Calculate continuous slope changes along a path
  3. Maximum Slope - Search for the point of maximum slope within an area
  4. Slope Statistics - Statistical distribution of slopes within an area