@joto
I think I have a question that relates to the issue @cdauth is struggling with.
What I attempted to do is to build a table with geometries from waterway
relations in OpenStreetMap.
Now I use the **object.as_geometrycollection()** function to generate a
geometry collection object of e.g. the Alpine Rhine waterway relation
(https://www.openstreetmap.org/relation/21222156), and subsequently insert each
of its member ways into a table using either **geom:geometries()** or
**geom.geometry_n()** and looping over the members.
According to the documentation, object.as_geometrycollection()
> It will contain all geometries which can be generated from node and way
> members of the relation in **order of those members**.
will return the members in the order as defined in the relation, if I
understand well.
However, if I e.g. want to know the osm ID of the n-th member way, I cannot use
the **object.members**. I would have expected object.members to return the
members of the relation _**in order of those members****_ as well. However, if
I attempt to grab e.g. the n-th geometry of the geometry collection using
**geom.geometry_n(n)** and also try to grab the n-th member as returned by
**object.members** by using **object.members[n]** and subsequently retrieve the
osm ID by using the **ref** field of the member table, I get back an osm ID
that does not correspond with the n-th way member of the relation, but another
osm ID. So it seems that the geometry collection, and the **object.members**
Lua table are out of sync, and **object.members** not sorted by the order in
which the relation members are stored in the relation.
Note that the relations I noticed this on, like the Alpine Rhine, do not
contain any sub-relations, just way members, and no nodes. So I would expect it
would be possible to have the geometry collections members and
**object.members** to be in sync.
Of course, it would be nice if I could somehow grab the geometry from the Lua
member table, similar to type,ref,role, e.g. **member_table.geometry**, similar
to **member_table.type/ref/role**, so that the it would be guaranteed to be in
sync.
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