Copy Memberships?

[maxerickson@…]

I wonder if a tool to "copy" relation memberships would be worth having.

Recent inspiration is from working with administrative boundaries for islands in Lake Huron. I, without realizing the consequences, used "Update Multipolygon", to add an island to several relations at once. JOSM proceeded to download all members of Lake Huron, at which time things got a little slow.

Thinking about other situations, when a highway is a member of multiple relations, it can get tedious to do something like add a short segment of dual carriageway (the easy way is to split a segment of the existing road for each side).

A tool that worked at the logical level and just added a way to the relations that the example way is part of would be helpful in both situations, as it is simple to reason about and so on.

[GerdP]

I don't understand what that tool would do.
You can select a new inner and "edit" the relation to add the new member without downloading all members. The problem: It is possible that you break the geometry of the multipolygon. Therefore we added a warning when this is done, see #18240
On the other hand, the "Update multipolygon" action might be improved to download the full relation instead of thousands of ways.
Anyhow, when working on such a huge multipolygon it is a good idea to give JOSM more heap memory with e.g. -Xmx4G to avoid performance problems.

[GerdP]

In 15531/josm:

see #18341: Improve performance when incomplete multipolygon is updated (Ctrl+Shift+B)
Only download a set of incomplete members if the number is not bigger than 100, else download the full relation.
This is expected to be much faster and less stressing for the server when the multipolygon is very complex (thousands of members).

[maxerickson@…]

The primary benefit would be situations where a new way is clearly a member of multiple relations that an existing way is a member of. The tool would examine the existing way, note relation memberships/roles/positions and then insert a selected new way in those relations, with those roles, in similar positions (probably the next item in the relation).

The operation is working at the logical level or however you want to put it, not considering the interpretation of the data at all, just doing what the user says (add this new way to the relations that old way belongs to).

I'm ambivalent about the utility of it, it would be useful in fairly narrow situations, I just wanted to throw the idea out there.

Thanks for the performance hint and the improvement in the download all members.

[stoecker]

Complex, little benefit, too much work.