Quick hack to take an OpenStreetMap bus route relation and convert it to an ordered series of points (suitable for use in a GTFS feed)

osm-relation2points.php

<?php

// This is the ID of the bus route relation.
$relation = '5838068';

// Retrieve the OSM for the object (which is XML of the relation and all of its children)
$xml = simplexml_load_file("http://www.openstreetmap.org/api/0.6/relation/$relation/full");

// First, we'll get all the ways that make up the "route" relation (assuming here there's only one!)
$relation_ways = array();
foreach ($xml->relation->member as $key => $member) {
  // We only want the components with the role "forward" or "backward", which omits stops and platforms
  if (((string)$member->attributes()->role == 'forward') or ((string)$member->attributes()->role == 'backward')) {
    $relation_ways[] = array('ref' => (string)$member->attributes()->ref, 'direction' => (string)$member->attributes()->role);
  }
}

// Next, we'll get ALL of the ways
$node = array();
foreach ($xml->way as $key => $member) {
  $nd = array();
  foreach ($member->nd as $key2 => $nd_member) {
    $nd[] = (string)$nd_member->attributes()->ref;
  }
  $way[(string)$member->attributes()->id] = $nd;
}

// Next, we'll get ALL of the nodes
$node = array();
foreach ($xml->node as $key => $member) {
  $node[(string)$member->attributes()->id] = array(
      (string)$member->attributes()->lat,
      (string)$member->attributes()->lon
    );
}

// Now we loop through each way in the relation...
$points = array();
foreach ($relation_ways as $key => $one_way) {
  // And if the way has a role of "forward" then we walk through the points in natural order
  if ($one_way['direction'] == 'forward') {
    foreach ($way[$one_way['ref']] as $key2 => $one_nd) {
      $points[] = $node[$one_nd][0]  . "," . $node[$one_nd][1] . "\n";
    }
  }
  // Otherwise we assume the role is "backcward" and walk through the points in reverse order
  else {
    foreach (array_reverse($way[$one_way['ref']]) as $key2 => $one_nd) {
      $points[] = $node[$one_nd][0]  . "," . $node[$one_nd][1] . "\n";
    }
  }
}

print_r($points);