how to retrieve datas from the endpoint of overpass-api

[dilbert2010]

good day dear experts here a phpbuilder,

currently want to dive into php with some real world projects +
connecting to the endpoint of Overpass.

a list of comma seperated values - is this correct.... ?

i want to translate the following overopass-turbo requests into a request that i run against the endpoint of the overpass-api ... like so,

$endpoint = 'http://overpass-api.de/api/interpreter';

i want to retrieve the data that i get with the following term -- that i use with the overpass-turbo-access;:

[out:csv(::id,::type,"name","addr:postcode","addr:city","addr:street","addr:housenumber","website"," contact:email=*")][timeout:600];
{{geocodeArea:Schweiz}}->.a;
( node(area.a)[amenity=hospital];
  way(area.a)[amenity=hospital];
  rel(area.a)[amenity=hospital];);
out;

so i have to port over the above mentioned code into the following approach:

# 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));

// 2.) Work with the XML Result

any idea!? Look forward to hear from you

[halojoy]

I dont see much php-code in your posted script.
But this is probably what you want from us here ... 🙂

[dilbert2010]

hello halojoy good evening

halojoy;11064283 wrote:

I dont see much php-code in your posted script.
But this is probably what you want from us here ... 🙂

many thanks for the answer - try to get some more insigths

The following is a little OSM Overpass API example with PHP SimpleXML - I love OSM, so let's show some useful examples.
The first part shows how you can query an Overpass Endpoint with standard PHP.

<?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));

well after the fetching the data the second part is also interesting.

That is querying the XML data.

Well - this is probably most easily done with xpath, the used PHP XML library are based on libxml which supports XPath 1.0 which covers the various querying needs very well.

The following example some - example - schools and tries to obtain their names as well.

//
// 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);
}

The key point here are the xpath queries. Two are used, the first one to get the nodes that have certain tags.

but - my question is: how to get the request on the endpoint in a better was ...

so that i can do this request in general - with all other options of a (general) requeast.

[dilbert2010]

btw - i want to

get an request that is running the following command ...

[out:csv(::id,::type,"name","addr:postcode","addr:city","addr:street","addr:housenumber","website"," contact:email=*")][timeout:600];
    {{geocodeArea:Schweiz}}->.a;
    ( node(area.a)[amenity=hospital];
      way(area.a)[amenity=hospital];
      rel(area.a)[amenity=hospital];);
    out;

how can i do that!?

[dilbert2010]

howdy halojoy - good evening,

halojoy;11064283 wrote:

I dont see much php-code in your posted script.
But this is probably what you want from us here ... 🙂

gardez : this runs like a charme

    <?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));

//
// 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);
}

//node[tag[@k = "amenity" and @v = "school"]]
//tag[@k = "name"]/@v'

$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));

and gives back the results

    me/martin/dev/php/o1.php on line 68
    linux-3645:/home/martin/dev/php # php o1.php
    Query returned 2799 node(s) and took 17.02055 seconds.

33 School(s) found:
#00: ID:332534486   [39.5018840,16.2722854]  Scuola Elementare
#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:2002566438  [39.1349460,16.0736446]  (unnamed)
#05: ID:2056891127  [39.4106679,16.8254844]  (unnamed)
#06: ID:2056892999  [39.4124687,16.8286119]  (unnamed)
#07: ID:2272010226  [39.4481717,16.2894353]  Scuola dell'infanzia San Francesco
#08: ID:2272017152  [39.4502366,16.2807664]  Scuola Media
#09: ID:2358307794  [39.5015031,16.3905965]  I.I.S.S. Liceo Statale V. Iulia
#10: ID:2358307796  [39.4926280,16.3853662]  Liceo Classico
#11: ID:2358307797  [39.4973761,16.3858275]  Scuola Media
#12: ID:2358307800  [39.5015527,16.3941156]  I.T.C. e per Geometri
#13: ID:2358307801  [39.4983862,16.3807796]  Istituto Professionale
#14: ID:2448031004  [38.6438417,16.3873106]  (unnamed)
[....]
    #31: ID:5297629775  [38.5768845,16.3263536]  Scuola Media Statale "Ignazio La Russa"
    #32: ID:5316865306  [39.0807997,17.1264225]  Enrico Fermi
    Query returned 3 node(s) and took 17.44780 seconds.

so far so good: - the only thing i wonder is why i get errors when doing minor changes

        # 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);
    }

if i do some additoinal lines here

list($name) = $school->xpath('tag[@k = "contact:website"]/@v');
    list($name) = $school->xpath('tag[@k = "contact:email"]/@v');

into the Foreach-Loop - so that it looks like so:

    {
        # Get the name of the school (if any), again with xpath
        list($name) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
        list($name) = $school->xpath('tag[@k = "contact:website"]/@v');
        list($name) = $school->xpath('tag[@k = "contact:email"]/@v');
        printf("#%02d: ID:%' -10s  [%s,%s]  %s\n", $index, $school['id'], $school['lat'], $school['lon'], $name);
    }

all this is entered into the second part of the code - the one that works with the XML-results

    //
    // 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) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
    list($name) = $school->xpath('tag[@k = "contact:website"]/@v');
    list($name) = $school->xpath('tag[@k = "contact:email"]/@v');
    printf("#%02d: ID:%' -10s  [%s,%s]  %s\n", $index, $school['id'], $school['lat'], $school['lon'], $name);
}

what is wanted here: i wanted to add /(or let me say to gain) some more infos eg Key:contact

    contact:phone
        contact:fax   

        contact:website
        contact:email

it is aimed to extend the xpath requests in the Foreach-Loop relatively to the Schools-Nodes

    tag[@k = "name"]/@v'
    tag[@k = "contact:website"]/@v'
    tag[@k = "contact:email"]/@v'

but if i do so - and have this foreach loop

    //
    // 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) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
    list($name) = $school->xpath('tag[@k = "contact:website"]/@v');
    list($name) = $school->xpath('tag[@k = "contact:email"]/@v');
    printf("#%02d: ID:%' -10s  [%s,%s]  %s\n", $index, $school['id'], $school['lat'], $school['lon'], $name);
}

i get the errors

    linux-3645:/home/martin/dev/php # php o2.php
    Query returned 2799 node(s) and took 6.22443 seconds.

33 School(s) found:
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 42
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 43
#00: ID:332534486   [39.5018840,16.2722854] 
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 42
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 43
#01: ID:1428094278  [39.3320912,16.1862820] 
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 42
PHP Notice:  Undefined offset: 0 in /home/martin/dev/php/o2.php on line 43
#02: ID:1822746784  [38.9075566,16.5776597]  

Well - serious errors : probably caused by some issues with the decoding and unwrapping

list($a, $b, $c…) = $array

we decode the content of the $array into the variables - wich is a short form for

$a = $array[0]; $b = $array[1]; $c = $array[2]; …

in some cases i unfortunatly do not have any Tags with the contact:website or contact:email.

so - we can work aroound this

1 choose other variables that $name - otherwise we overwrite the gained infos
2.use the trick to attach at the Array a Default string

Because not all school nodes have a name, a default string is provided for display purposes by adding it to the (then empty) result array:

list($name) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
                                                    ^^^^^^^^^^^^^^^
                                                Provide Default Value

so here we can do like so:

# Get the name of the school (if any), again with xpath
list($name) = $school->xpath('tag[@k = "name"]/@v') + ['(unnamed)'];
list($website) = $school->xpath('tag[@k = "contact:website"]/@v') + ['(no website)'];
list($email) = $school->xpath('tag[@k = "contact:email"]/@v') + ['(no email)'];
printf("#%02d: ID:%' -10s  [%s,%s]  %s %s %s\n", $index, $school['id'], $school['lat'], $school