PHP使用foreach遍历GeoJSON仅能获取单个Polygon坐标如何修复

问题根因 #

你当前代码仅能获取单个Polygon坐标的核心问题是foreach遍历范围写死了features[0]，仅读取了features数组的第一个元素，没有覆盖所有Feature；同时GeoJSON的Polygon类型coordinates为三层嵌套结构，直接遍历外层仅能拿到多边形环数组，无法直接获取坐标点。

修改后的完整代码 #

<?php
$str = '{"type":"FeatureCollection","features":[{"type":"Feature","properties":{},"geometry":{"type":"Polygon","coordinates":[[[9.78281,54.923985],[9.80341,54.901586],[9.819803,54.901981],[9.83551,54.908396],[9.825897,54.91481],[9.822721,54.927142],[9.807186,54.927931],[9.792767,54.926797],[9.78281,54.923985]]]},{"type":"Feature","properties":{},"geometry":{"type":"Polygon","coordinates":[[[9.914474,54.930298],[9.901085,54.912343],[9.849243,54.912146],[9.846497,54.928917],[9.890785,54.946865],[9.930267,54.937399],[9.914474,54.930298]]]}}]}';

$polygon = json_decode($str);

// 遍历所有Feature对象
foreach($polygon->features as $singleFeature) {
    // 遍历当前Polygon的外环坐标点
    foreach($singleFeature->geometry->coordinates[0] as $coordinate) {
        print_r($coordinate);
    }
}
?>

可选适配方案 #

如果你的数据中存在带内环（空心）的Polygon，可调整坐标遍历逻辑，覆盖所有环的坐标：

foreach($polygon->features as $singleFeature) {
    // 遍历当前Polygon的所有环（外环+所有内环）
    foreach($singleFeature->geometry->coordinates as $ring) {
        // 遍历单个环的所有坐标点
        foreach($ring as $coordinate) {
            print_r($coordinate);
        }
    }
}

内容的提问来源于stack exchange，提问作者JonasW