Sequence of the nodes (node id's) of lines

Help and support
1

Hallo,
I’d like to know the sequence of the nodes of the line and I need a little help.
For example there is a line with id=412636792 (Way: ‪AB OMV Austria Exploration & Production‬ (‪412636792‬) | OpenStreetMap)
and it has 21 nodes with the following id’s:
324300340; 324300344; 4140119176; 328858625; 4140119177; 324300347; 4140119178; 1709516280; 4140119179; 339706231; 4140119180; 1560583323; 4140119181; 339706232; 4140119182; 1709516281; 6043439544; 1560583341; 4140119183; 1560583346; 339706235.

How can I know which is the first/last node and which is the next, …? so I’d like to know the sequence of the node id’s.

Thanks in advance.
Regads,
Cerma

1 Like
2

Fortunately, osm.org keeps nodes in their order anyway, so your list is already correctly ordered (starting with #324300340 and ending at #339706235).

Unless I’m missing something, there’s no extra processing you need to do to get the correct order of nodes.

1 Like
3

Thank you. Does it mean, that when a new node inserted into an existing line (i.e. because something changed in the line), then OSM can handle this situtation?

NodeSequence
NodeSequence1750×981 128 KB

So, in case of attached situation will be the result of the query of the nodes the following?

324300340; 324300344; 4140119176; 328858625; 4140119177; 324300347; 4140119178; 1709516280; 4140119179; 339706231; 4140119180; 1560583323; 4140119181; 339706232; 4140119182; 1709516281; [id of inserted new node]; 6043439544; 1560583341; 4140119183; 1560583346; 339706235.

Best regards,

Cerma

4

I don’t the answer to your question, but if you open the line in JOSM it’s easy to see what id’s nodes have by clicking on them.

1 Like
5

Yes, exactly the way as you described in your example.

1 Like
6

Thank you.

7

Thank you. But as I guess in this case there is an internal (hidden) id in the OSM database, which determine the sequence…

8

No, the way object is described as an array of nodes with the ID as the value.

2 Likes
9

As an example, this is what a node added to a way looks like in the *.osm file format that JOSM uses for locally saved edits. JOSM uses a negative id / ref number for new nodes that haven’t been uploaded yet.

...
<node id='-138605' action='modify' lat='53.48353611317' lon='-2.33880847827' />
...
<way id='1159196555' action='modify' timestamp='2023-04-02T16:01:51Z' uid='89098' user='InsertUser' version='1' changeset='134420557'>
    <nd ref='10779934280' />
    <nd ref='10779934279' />
    <nd ref='10779934269' />
    <nd ref='10779934278' />
    <nd ref='-138605' />
    <nd ref='10779934277' />
    <nd ref='10779934271' />
    <nd ref='10779934276' />
    <nd ref='10779934275' />
    <nd ref='10779934274' />
    <nd ref='10779934273' />
    <tag k='highway' v='service' />
    <tag k='service' v='parking_aisle' />
  </way>
...
2 Likes
10

I suspect the aspect the OP is missing is that we always list all way nodes in the new* order when updating a way via the API.

* this is true even if we are only modifying tags, except that in that case it is just a restatement of the existing data.

4 Likes
11

Hallo Simon,
Probably, but what you mean OP?

regards,

12

Original Poster aka you :grinning:

1 Like
13

Hallo Toni,
it means, that the way object stored as array, so in this case the “hidden” ID I mentioned earlier is the array element id, isn’t?
regards,

14

Yeah, the index in the array represents the position in the sequence.

1 Like
15

Thank you :slightly_smiling_face:, and yes.

What I don’t get is that if I download the ways and nodes and try to build up the line (sequence of nodes) logically in my application, how can I know the order of the sequence (order) of the nodes.
If it is the situation, I have to record the nodes order (by creating an own order id) for the use later.

Regards,

16

If you download using Overpass or the API, you’ll get XML data:

  <way id="769513663">
    <nd ref="2233422872"/>
    <nd ref="2233422879"/>
    <nd ref="2233422889"/>
    <nd ref="2233422897"/>
    <nd ref="3389568592"/>
    <tag k="highway" v="residential"/>
  </way>

The sequence of the nodes is given by their appearance in the way description.

2 Likes
17

Thank you, so when a new node is inserted in a way, then the nodes are moved by one?

An example for the way (id=412636792):
“way nodes” as array:

nodes[0]=324300340,
*… *
nodes[15]=1709516281,
nodes[16]=6043439544,
…
nodes[20]=339706235

after a new node inserted between 1709516281 and 6043439544 (see picture):

nodes[0]=324300340,
*… *
nodes[15]=1709516281,
nodes[16]=new node id
nodes[17]=6043439544,
…
nodes[21]=339706235

Isn’t?

Regards,

1 Like
18

Correct, that’s what you get with a second download after uploading the changes (in JOSM, …).

The “new node id” is determined by the OSM DB-SW, not by you though. That’s why JOSM chooses a negative number as internal value.

Q: what does JOSM actually upload then? The negative number or an empty value (in the XML)?

1 Like
19

I get it: my dilemma is that
a) should I create an own “node-order-index” or
b) can I download/get a “node-order-index” directly from OSM
during or after download using Overpass or the API?

Regards,

20

I see. Thank you.