Determine Angle of Street by Parsing an Overpass-Turbo output xml

Question

I am currently downloading all the street intersections from a bounding box using the query below (see it on overpass).

<query type="way" into="hw">
  <has-kv k="highway"/>
  <has-kv k="highway" modv="not" regv="footway|cycleway|path|service|track"/>
  <bbox-query e="9.1775" n="45.8428" s="45.7581" w="8.9904"/>
</query>

<foreach from="hw" into="w">
  <recurse from="w" type="way-node" into="ns"/>
  <recurse from="ns" type="node-way" into="w2"/>
  <query type="way" into="w2">
    <item set="w2"/>
    <has-kv k="highway"/>
    <has-kv k="highway" modv="not" regv="footway|cycleway|path|service|track"/>
  </query>
  <difference into="wd">
    <item set="w2"/>
    <item set="w"/>
  </difference>
  <recurse from="wd" type="way-node" into="n2"/>
  <recurse from="w"  type="way-node" into="n3"/>
  <query type="node">
    <item set="n2"/>
    <item set="n3"/>
  </query>
  <print/>
</foreach>

The output is a 92 pages doc (including duplicates) containing nodes(node id, lat and long). I am extracting the latitudes and longitudes in order to compose a Google Street View Image link because i want to download for each point the corresponding image. In the composition of the link I also want to calculate the heading-angle of the street;

I know the math formula needed but it requires 2 lat and 2 long (from 2 points in the same street) and my problem is that the nodes in the output file don't have a specific order. Therefore, i cannot calculate the angle between two consecutive nodes.

I was thinking of sorting the lat or long in asc/desc order because in this way i might find the points in the same street. Is this method valid or i can solve it in an easier way? Is there any more efficient way to find all the street intersections?

Answer 1

You need a part of the answer for ways. Ways in OSM are ordered lists of node references.

So the part of the answer what you need should looks like:

<way id="22940464">
    <nd ref="272304964"/><!-- First node -->
    <nd ref="273206415"/><!-- Second node -->
    <nd ref="273206424"/>
    <nd ref="1827734835"/>
    <nd ref="272307378"/>
    <nd ref="3263545766"/>
    <nd ref="247110585"/><!-- Last node -->
    <tag k="highway" v="unclassified"/>
    <tag k="name" v="Via Maurizio Monti"/>
    <tag k="oneway" v="yes"/>
</way>

Where <nd ref="1827734835"/> refers to node 1827734835. And below details for that node with coordinates:

<node id="1827734835" lat="45.8122890" lon="9.0889686"/>

---

I've rewrited your query with OverpassQL:

[out:xml][timeout:25];

// filter ways
way[highway][highway!~"footway|cycleway|path|service|track"]({{bbox}})->.hw;

// foreach way
foreach.hw->.eachw(
  // get ways, which shares same nodes minus current way
  // into .otherws
  node(w.eachw)->.ns;
  way(bn.ns)[highway][highway!~"footway|cycleway|path|service|track"]->.w2;
  (way.w2; - way.eachw;)->.otherws;

  // get shared nodes
  node(w.otherws)->.n2;
  node(w.eachw)->.n3;
  (((node.n2; node.n3;) -(node.n2; - node.n3;);) -(node.n3; - node.n2;);)->.shrdnodes;

  // ways which are in junction
  way(bn.shrdnodes)->.outways;

  // union ways and nodes
  (way.outways; node.shrdnodes;); out;

  // dirty hack
  //(node(100000); node(w.outways); node(100000);); out;  
);

At this point, you'll get a shared points, and ways after them. You may send separate querys to get highways geometries, or uncomment a row after //dirty hack.

What those hack does and why we need it. Without it, you'll got:

• junction nodes
• junction ways, but without a nodes

the re is no option for overpass to get a list of set which object belongs to, or mark your result set in any other way.

So I use node(100000) (node with id=100000) as a bracket for my output to group nodes, which are not a shared nodes, but just a nodes to build full geometry of a way. If there be an option to include datasets to answer as a meta for objects, I could just add all nodes with different sets.

So the overpass answwer looks like

<!-- my shared nodes which I looking for -->
<node id="175040709" lat="56.8281187" lon="60.6118371"/>
<node id="175048158" lat="56.8278883" lon="60.6097093"/>
<node id="410047434" lat="56.8274783" lon="60.6059228"/>

<!--ways which are in junction -->
<way id="20107663">
    <nd ref="175040709"/>
    <nd ref="803415497"/>
    <!-- skip some xml here -->
  </way>
  <way id="34939324">
    <!-- skip some xml here -->
  </way>
  <way id="56640542">
    <!-- skip some xml here -->
  </way>
  <way id="118465904">
    <!-- skip some xml here -->
  </way>
  <way id="148027458">
    <!-- skip some xml here -->
  </way>

<!-- my bracket node -->
  <node id="100000" lat="58.4215584" lon="15.6183153"/>

<!-- nodes to build full geometry -->
  <node id="175040705" lat="56.8283647" lon="60.6140898">
    <tag k="highway" v="traffic_signals"/>
  </node>
  <node id="175040709" lat="56.8281187" lon="60.6118371"/>
  <node id="175048158" lat="56.8278883" lon="60.6097093"/>
  <node id="175048160" lat="56.8274040" lon="60.6052596"/>
  <node id="176277604" lat="56.8351416" lon="60.6094024">
  <!-- more nodes here -->

<!-- my bracket node again-->
  <node id="100000" lat="58.4215584" lon="15.6183153"/>

<!-- next portion of junction ways and nodes -->