react-native - react 原生 MapView : what is latitudeDelta longitudeDelta

Question

在 react native mapview 的示例中它们有 latitudeDelta 和 longitudeDelta。它等于高度和宽度吗？在什么单位？根据他们的github comment ， 它说

Distance between the minimum and the maximum latitude/longitude to be displayed.

但这对我没有帮助。我想知道用户在 map 上看到了什么。

Answer 1

你需要

"centroid": {
    "latitude": "24.2472",
    "longitude": "89.920914"
},
"boundingBox": {
    "southWest": {
        "latitude": "24.234631",
        "longitude": "89.907127"
    },
    "northEast": {
        "latitude": "24.259769",
        "longitude": "89.934692"
    }
}

或类似的数据来正确计算 latitudeDelta 和 longitudeDelta。

下面是 react/react-native 的演示代码。

componentDidMount() {
    const { width, height } = Dimensions.get('window');
    const ASPECT_RATIO = width / height;

    const lat = parseFloat(centroid.latitude);
    const lng = parseFloat(centroid.longitude);
    const northeastLat = parseFloat(boundingBox.northEast.latitude);
    const southwestLat = parseFloat(boundingBox.southWest.latitude);
    const latDelta = northeastLat - southwestLat;
    const lngDelta = latDelta * ASPECT_RATIO;

    this.setState({
      region: {
        latitude: lat,
        longitude: lng,
        latitudeDelta: latDelta,
        longitudeDelta: lngDelta
      }
    })     
}