duplicate a way in-place

[aharvey]

JOSM core should provide a way to duplicate a way but reusing the original nodes rather than creating duplicate nodes.

I built a plugin for this at ​https://gitlab.com/alantgeo/josm-duplicate-way-inplace but in my view it should be a core functionality.

[stoecker]

There are multiple methods to reach that already now (e.g. the follow function, or later fixing duplicate nodes) and I don't see a real importance of that feature.

[aharvey]

Yes but in my opinion these are poor workarounds.

Follow requires a lot of manual work. You need to tell it which way to follow upon a junction, and for long ways you're holding down the F key for many many seconds. It's error prone as trying to select the correct way to follow at each junction often leads to missing a node, or inserting a new node into the way, then you need deselect everything to redo that messed up junction selection, then trying to merge all the short segments you did with the follow, and on top of that depending which node you start on for the Follow, you might end up lengthening an existing way rather than drawing a new one.

The Follow feature is useful for doing exactly that, following another way, but it's not a duplicate way in place tool substitute.

Same goes for "fixing" later. It's multiple steps, copy, paste at source position, now delete the tags since you only wanted to duplicate the geometry, not copy the tags, run the validator and fix it, hoping that it's not merging other nodes unrelated to your way duplication. What longer, because the validator can be slow on large datasets. Not to mention that's bad UX, how would anyone know that "it's okay just leave the duplicate nodes there, the validator will let you fix those later", most likely the user will just find there is no tool for this.

The better UX is to rename Edit > Duplicate to "Duplicate with a position offset", then add a new "Duplicate in-place (new nodes)", then "Duplicate in-place (re-use nodes)" if it was a way selected.

In terms of real-world uses...

The [Simple 3D Buildings scheme](​https://wiki.openstreetmap.org/wiki/Simple_3D_Buildings) says to place a building=* way for the overall footprint, then another one or more building:part=* inside it for the 3D shapse. So typically for a podium and tower style building you'll need two ways for the base part, but sharing the same nodes, ie. draw once as building=* then duplicate in-place with shared nodes as the lower building:part=*.

Another scenario is when I want to "glue" two way areas together but avoid using "follow" due to the aforementioned reasons.

Another use case would be when you want tag the same thing with different ways.

I'm sure there's other use cases too.