以下是我编译的一个带有 PHP SimpleXML 的 OSM Overpass API 小示例,因为我们这里没有 PHP 并且我喜欢 OSM,所以让我们展示一些有用的示例。
第一部分展示了如何使用标准 PHP 查询 Overpass Endpoint。您不需要该部分,因为您已经将数据保存在硬盘上:
<?php
/**
* OSM Overpass API with PHP SimpleXML / XPath
*
* PHP Version: 5.4 - Can be back-ported to 5.3 by using 5.3 Array-Syntax (not PHP 5.4's square brackets)
*/
//
// 1.) Query an OSM Overpass API Endpoint
//
$query = 'node
["amenity"~".*"]
(38.415938460513274,16.06338500976562,39.52205163048525,17.51220703125);
out;';
$context = stream_context_create(['http' => [
'method' => 'POST',
'header' => ['Content-Type: application/x-www-form-urlencoded'],
'content' => 'data=' . urlencode($query),
]]);
# please do not stress this service, this example is for demonstration purposes only.
$endpoint = 'http://overpass-api.de/api/interpreter';
libxml_set_streams_context($context);
$start = microtime(true);
$result = simplexml_load_file($endpoint);
printf("Query returned %2\$d node(s) and took %1\$.5f seconds.\n\n", microtime(true) - $start, count($result->node));
对你来说,第二部分更有趣。那就是查询您已经拥有的 XML 数据。使用 xpath 最容易做到这一点,使用的 PHP XML 库基于 libxml,它支持XPath 1.0,它很好地涵盖了各种查询需求。
以下示例列出了所有学校并尝试获取它们的名称。我还没有涵盖翻译,因为我的示例数据没有这些,但您也可以查找包括翻译在内的所有类型的名称,并且只喜欢特定的名称):
//
// 2.) Work with the XML Result
//
# get all school nodes with xpath
$xpath = '//node[tag[@k = "amenity" and @v = "school"]]';
$schools = $result->xpath($xpath);
printf("%d School(s) found:\n", count($schools));
foreach ($schools as $index => $school)
{
# Get the name of the school (if any), again with xpath
list($name) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
printf("#%02d: ID:%' -10s [%s,%s] %s\n", $index, $school['id'], $school['lat'], $school['lon'], $name);
}
这里的关键点是 xpath 查询。使用了两个,第一个用于获取具有特定标签的节点。我认为这对你来说是最有趣的:
//node[tag[@k = "amenity" and @v = "school"]]
这行说:给我所有的节点元素,其中有一个标签元素,其中k属性值"amenity"和v属性值"school"。这是您必须过滤掉那些标有 amenity school的节点的条件。
再次使用 xpath,现在相对于那些学校节点查看是否有名称,如果有,则获取它:
tag[@k = "name"]/@v'
这一行说:相对于当前节点,给我来自标签元素的v属性,作为k属性值"name"。如您所见,某些部分再次与之前的行相似。我认为你们都可以根据自己的需要采用它们。
因为并非所有学校节点都有名称,所以通过将默认字符串添加到(然后为空)结果数组中来提供默认字符串以供显示:
list($name) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
^^^^^^^^^^^^^^^
Provide Default Value
所以这里是我对该代码示例的结果:
Query returned 907 node(s) and took 1.10735 seconds.
10 School(s) found:
#00: ID:332534486 [39.5017565,16.2721899] Scuola Primaria
#01: ID:1428094278 [39.3320912,16.1862820] (unnamed)
#02: ID:1822746784 [38.9075566,16.5776597] (unnamed)
#03: ID:1822755951 [38.9120272,16.5713431] (unnamed)
#04: ID:1903859699 [38.6830409,16.5522243] Liceo Scientifico Statale A. Guarasci
#05: ID:2002566438 [39.1347698,16.0736924] (unnamed)
#06: ID:2056891127 [39.4106679,16.8254844] (unnamed)
#07: ID:2056892999 [39.4124687,16.8286119] (unnamed)
#08: ID:2272010226 [39.4481717,16.2894353] SCUOLA DELL'INFANZIA SAN FRANCESCO
#09: ID:2272017152 [39.4502366,16.2807664] SCUOLA MEDIA
我希望这已经很有用了,如果您有更多澄清问题,请告诉我。
(by rbwilkinson):这是您可以添加其他参数以查找其他值的方式。以下示例查找一公里内的其他属性:
$query = 'node
["addr:postcode"~"RM12"]
(51.5557914,0.2118915,51.5673083,0.2369398);
node
(around:1000)
["amenity"~"fast_food"];
out;';
$context = stream_context_create(['http' => [
'method' => 'POST',
'header' => ['Content-Type: application/x-www-form-urlencoded'],
'content' => 'data=' . urlencode($query),
]]);
$endpoint = 'http://overpass-api.de/api/interpreter';
libxml_set_streams_context($context);
$result = simplexml_load_file($endpoint);
printf("Query returned %2\$d node(s) and took %1\$.5f seconds.\n\n", microtime(true) - $start, count($result->node));
}