为GeoJSON数据生成BoundingBox [英] Generating BoundingBox for GeoJSON data

问题描述

我正在使用Google提供的Android Map Utils(compile 'com.google.maps.android:android-maps-utils:0.4')在地图上绘制GeoJSON多边形.但是，我得到的GeoJSON不包含边界框，因此有时地图很远.这是我回来的多边形东西的一个例子:

I'm drawing GeoJSON polygons on my map using the Android Map Utils that Google provides (compile 'com.google.maps.android:android-maps-utils:0.4'). However, the GeoJSON I get does not include a bounding box, so sometimes the map is way off. Here's an example of the polygon stuff I get back:

{"type":"Polygon","coordinates":[[[-88.138825,30.719378],[-88.138927,30.719386],[-88.139181,30.719409],[-88.139433,30.719429],[-88.139438,30.719429],[-88.139633,30.719446],[-88.139848,30.719461],[-88.140194,30.719487],[-88.140316,30.719495],[-88.140488,30.719505],[-88.140857,30.719522],[-88.141193,30.719544],[-88.141495,30.719559],[-88.141733,30.719571],[-88.142232,30.719596],[-88.142378,30.719602],[-88.142709,30.719616],[-88.143286,30.719639],[-88.143726,30.719657],[-88.14423,30.719677],[-88.144496,30.71969],[-88.144954,30.719712],[-88.146015,30.719757],[-88.146594,30.719782],[-88.146871,30.719794],[-88.147776,30.719835],[-88.148589,30.719868],[-88.148847,30.719876],[-88.149387,30.719903],[-88.150273,30.719944],[-88.151101,30.719981],[-88.151919,30.720016],[-88.152748,30.720054],[-88.153862,30.720098],[-88.154916,30.72014],[-88.156111,30.720194],[-88.157177,30.720241],[-88.157649,30.720266],[-88.158093,30.720292],[-88.158425,30.720314],[-88.158771,30.720349],[-88.15907,30.72038],[-88.159393,30.720415],[-88.160031,30.720494],[-88.160662,30.72057],[-88.161215,30.720637],[-88.161742,30.720696],[-88.162071,30.720736],[-88.16195,30.720897],[-88.161855,30.721036],[-88.161782,30.721148],[-88.161692,30.721293],[-88.161655,30.721359],[-88.161616,30.72142],[-88.161584,30.721479],[-88.161543,30.721555],[-88.161508,30.721632],[-88.161476,30.721714],[-88.161457,30.721782],[-88.161442,30.721843],[-88.161432,30.721883],[-88.161429,30.721898],[-88.161416,30.721954],[-88.161402,30.722014],[-88.161392,30.722065],[-88.161384,30.722116],[-88.161375,30.722182],[-88.16137,30.722242],[-88.161367,30.722323],[-88.161369,30.722429],[-88.161373,30.722566],[-88.161376,30.722761],[-88.161375,30.723117],[-88.161375,30.723257],[-88.16137,30.72343],[-88.161361,30.723634],[-88.16136,30.723863],[-88.161359,30.724048],[-88.161364,30.724241],[-88.161365,30.724525],[-88.16137,30.724805],[-88.161371,30.724934],[-88.161371,30.725025],[-88.161374,30.725131],[-88.161375,30.725532],[-88.161374,30.725576],[-88.161368,30.725633],[-88.161362,30.725683],[-88.16136,30.725726],[-88.161361,30.725776],[-88.161362,30.725839],[-88.161366,30.725911],[-88.161379,30.726238],[-88.161378,30.726573],[-88.161377,30.726897],[-88.161366,30.727084],[-88.161366,30.727149],[-88.161371,30.727222],[-88.161379,30.72733],[-88.161379,30.727437],[-88.161378,30.727548],[-88.161375,30.727627],[-88.161357,30.727818],[-88.161351,30.727923],[-88.161352,30.728014],[-88.161363,30.728186],[-88.16137,30.728395],[-88.161369,30.72872],[-88.161372,30.728957],[-88.161372,30.729211],[-88.161379,30.729351],[-88.161386,30.72945],[-88.161393,30.729556],[-88.161396,30.729655],[-88.161394,30.729824],[-88.161403,30.730129],[-88.161405,30.730268],[-88.161405,30.730457],[-88.161405,30.730763],[-88.161407,30.730923],[-88.161399,30.731075],[-88.161392,30.731214],[-88.161388,30.731399],[-88.161394,30.731602],[-88.1614,30.731923],[-88.161402,30.732116],[-88.161395,30.732547],[-88.161405,30.732797],[-88.161418,30.733154],[-88.161417,30.733291],[-88.161394,30.733911],[-88.161366,30.734341],[-88.161317,30.734959],[-88.161275,30.735447],[-88.161241,30.735907],[-88.161219,30.736167],[-88.161189,30.736516],[-88.161175,30.736742],[-88.161137,30.737199],[-88.161115,30.737806],[-88.161113,30.738298],[-88.161098,30.738838],[-88.161087,30.739417],[-88.161091,30.73989],[-88.161094,30.740051],[-88.161103,30.740272],[-88.161115,30.74039],[-88.161129,30.740519],[-88.161137,30.740623],[-88.161141,30.740794],[-88.161139,30.741026],[-88.16114,30.741196],[-88.161139,30.741207],[-88.160888,30.741207],[-88.160501,30.741239],[-88.160319,30.741246],[-88.160169,30.741256],[-88.160092,30.741259],[-88.160012,30.741266],[-88.15993,30.741275],[-88.159829,30.741294],[-88.159698,30.741321],[-88.159558,30.741336],[-88.159442,30.741339],[-88.159311,30.741336],[-88.159192,30.741321],[-88.159042,30.74129],[-88.15892,30.741243],[-88.158603,30.74109],[-88.157116,30.7401],[-88.156761,30.739874],[-88.156503,30.739646],[-88.156348,30.739506],[-88.156203,30.739375],[-88.155937,30.739118],[-88.155858,30.739047],[-88.155775,30.738987],[-88.155698,30.738943],[-88.155132,30.738695],[-88.154993,30.738633],[-88.154833,30.738573],[-88.154655,30.738522],[-88.153851,30.738351],[-88.153642,30.738305],[-88.153508,30.738289],[-88.153379,30.738265],[-88.153268,30.738247],[-88.153164,30.738224],[-88.153104,30.738193],[-88.153035,30.738138],[-88.152764,30.737898],[-88.152599,30.737736],[-88.152537,30.73767],[-88.152488,30.737632],[-88.152424,30.737614],[-88.152354,30.737621],[-88.152231,30.73763],[-88.151638,30.7377],[-88.151547,30.737709],[-88.151478,30.737711],[-88.151423,30.737709],[-88.151369,30.737685],[-88.150774,30.737301],[-88.150566,30.737133],[-88.150513,30.737064],[-88.150293,30.736767],[-88.150214,30.736663],[-88.150156,30.73658],[-88.150095,30.736495],[-88.150037,30.736417],[-88.15,30.736359],[-88.149954,30.736326],[-88.149898,30.736294],[-88.149803,30.736258],[-88.149727,30.736238],[-88.14966,30.736233],[-88.14956,30.736236],[-88.149547,30.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我只是通过执行以下操作将其添加到地图中:

And I'm just adding it to the map by doing:

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

但是，由于KVP数据中没有提供界限"，因此，每次尝试执行layer.getBoundingBox()时，我总是得到null的返回值.一旦知道坐标，是否有办法自己生成边界框?

However, because there are no "bounds" supplied in the KVP data, so any time I try to do, layer.getBoundingBox(), I always get a return value of null. Is there a way to generate the bounding box myself once I know the coordinates?

推荐答案

查看

Looking at the sources of GeoJsonLayer.java and GeoJsonParser.java it's obvious that there's no code to calculate the bounding box. Even the parseFeatureCollection() method just parses the bounding box if it's in the GeoJSON data.

但是边界框是 LatLngBounds 对象，并且该类具有嵌套的 Builder 类，可用于构建LatLngBounds对象:

However the bounding box is a LatLngBounds object and the class has a nested Builder class which can be used to build a LatLngBounds object:

// 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，如果只绘制GeoJsonPolygons，则获得边框的麻烦就不那么多了.

So, if you have only GeoJsonPolygons to draw it's not that much hassle to get a bounding box.

要获得更完整的解决方案，您将必须构建更复杂的机制以从任何 GeoJsonGeometry的实现界面.首先是要区分 GeoJsonGeometryCollection 和其他所有内容:

For a more complete solution you would have to build a more elaborate mechanism to extract the coordinates from any GeoJSON geometry object type. They are all implementations of the GeoJsonGeometry interface. The first thing is to differentiate between GeoJsonGeometryCollection and all the rest:

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)如下:

The actual code (may have bugs) for extracting the coordinates would be something like:

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:

You would then use the code like:

LatLngBounds bb = getLatLngBoundingBox(layer);

这篇关于为GeoJSON数据生成BoundingBox的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！