android - 为 GeoJSON 数据生成 BoundingBox

Question

我正在使用 Google 提供的 Android Map Utils(compile 'com.google.maps.android:android-maps-utils:0.4')在我的 map 上绘制 GeoJSON 多边形。但是，我得到的 GeoJSON 不包含边界框，因此有时 map 会偏离。这是我返回的多边形示例:

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我只是通过以下方式将其添加到 map 中:

            geoJsonObject = new JSONObject(response);
            GeoJsonLayer layer = new GeoJsonLayer(getMap(), geoJsonObject);
            layer.addLayerToMap();

但是，因为 KVP 数据中没有提供“边界”，所以每当我尝试执行 layer.getBoundingBox() 时，我总是得到 null 的返回值。有没有办法在我知道坐标后自己生成边界框？

Answer 1

查看 GeoJsonLayer.java 的来源和 GeoJsonParser.java很明显，没有计算边界框的代码。即使是 parseFeatureCollection()如果边界框在 GeoJSON 数据中，则该方法只解析边界框。

但是边界框是一个 LatLngBounds对象和类有一个嵌套的 Builder可用于构建 LatLngBounds 对象的类:

// Get the bounding box builder.
LatLngBounds.Builder builder = LatLngBounds.builder();

// Get the coordinates
for (GeoJsonFeature feature : layer.getFeatures()) {
    if (feature.hasGeometry()) {
        GeoJsonGeometry geometry = feature.getGeometry();

        List<? extends List<LatLng>> lists =
                ((GeoJsonPolygon) geometry).getCoordinates();

        // Feed the coordinates to the builder.
        for (List<LatLng> list : lists) {
            for (LatLng latLng : list) {
                builder.include(latLng);
            }
        }
    }
}

// Assign the builder's return value to a bounding box.
LatLngBounds bb = builder.build();

因此，如果您只有 GeoJsonPolygons 可以绘制，那么获取边界框并不是那么麻烦。

要获得更完整的解决方案，您必须构建更精细的机制来从任何 GeoJSON geometry object type 中提取坐标.它们都是 GeoJsonGeometry 的实现界面。首先要区分GeoJsonGeometryCollection以及所有其他的:

private LatLngBounds getLatLngBoundingBox(GeoJsonLayer layer) {

    List<LatLng> coordinates = new ArrayList<>();

    for (GeoJsonFeature feature : layer.getFeatures()) {

        if (feature.hasGeometry()) {
            GeoJsonGeometry geometry = feature.getGeometry();

            if (geometry.getType().equals("GeometryCollection")) {
                List<GeoJsonGeometry> geometries =
                        ((GeoJsonGeometryCollection)geometry).getGeometries();

                for (GeoJsonGeometry geom : geometries) {
                    coordinates.addAll(getCoordinatesFromGeometry(geom));
                }
            }
            else {
                coordinates.addAll(getCoordinatesFromGeometry(geometry));
            }
        }
    }

    // Get the bounding box builder.
    LatLngBounds.Builder builder = LatLngBounds.builder();

    // Feed the coordinates to the builder.
    for (LatLng latLng : coordinates) {
        builder.include(latLng);
    }

    LatLngBounds boundingBoxFromBuilder = builder.build();

    //return boundingBox;
    return boundingBoxFromBuilder;
}

提取坐标的实际代码(可能有错误)类似于:

private List<LatLng> getCoordinatesFromGeometry(GeoJsonGeometry geometry) {

    List<LatLng> coordinates = new ArrayList<>();

    // GeoJSON geometry types:
    // http://geojson.org/geojson-spec.html#geometry-objects

    switch (geometry.getType()) {
        case "Point":
            coordinates.add(((GeoJsonPoint) geometry).getCoordinates());
            break;
        case "MultiPoint":
            List<GeoJsonPoint> points = ((GeoJsonMultiPoint) geometry).getPoints();
            for (GeoJsonPoint point : points) {
                coordinates.add(point.getCoordinates());
            }
            break;
        case "LineString":
            coordinates.addAll(((GeoJsonLineString) geometry).getCoordinates());
            break;
        case "MultiLineString":
            List<GeoJsonLineString> lines =
                    ((GeoJsonMultiLineString) geometry).getLineStrings();
            for (GeoJsonLineString line : lines) {
                coordinates.addAll(line.getCoordinates());
            }
            break;
        case "Polygon":
            List<? extends List<LatLng>> lists =
                    ((GeoJsonPolygon) geometry).getCoordinates();
            for (List<LatLng> list : lists) {
                coordinates.addAll(list);
            }
            break;
        case "MultiPolygon":
            List<GeoJsonPolygon> polygons =
                    ((GeoJsonMultiPolygon) geometry).getPolygons();
            for (GeoJsonPolygon polygon : polygons) {
                for (List<LatLng> list : polygon.getCoordinates()) {
                    coordinates.addAll(list);
                }
            }
            break;
    }

    return coordinates;
}

然后您将使用如下代码:

LatLngBounds bb = getLatLngBoundingBox(layer);