[Indoor] repeat_on and unrolling other tag values

[Volker Krause]

On Montag, 27. Mai 2024 20:18:26 CEST Tobias Knerr via indoor wrote:
> On 27.05.24 at 17:47, Volker Krause wrote:
> > https://www.openstreetmap.org/way/1134007505 (example, repeats in that
> > building).
> > 
> > (1) pure repeat_on vs. level + repeat_on use
> 
> This aspect of the mapping is correct.
> 
> The mental model we had when writing SIT was that you would map the
> feature at one (arbitrarily chosen) level the same way you normally
> would and then "copy" it to the other levels using repeat_on. I do
> acknowledge that omitting the level tag entirely and listing all the
> levels in repeat_on would work just as well – I don't remember that we
> consciously considered that alternative at the time.

Thanks, that is indeed something I had misunderstood so far then.

> > Might be worth clarifying, but from an implementor's perspective always
> > just using the union seems safe I guess, or is there a semantic to a
> > combined level/repeat_on use I'm missing here?
> 
> If the level value is just a single level, using the union is definitely
> correct.
> 
> However, there is a possible complication when repeat_on is combined
> with multiple levels or level ranges. I would consider it more natural
> to interpret something such as level=0-1 + repeat_on=2;4;6 to represent
> 4 rooms, each of which is 2 levels high; rather than 5 rooms (which
> would be the result if you calculate the union).
> 
> Note that I would recommend against ever using something like that when
> mapping.

Right, that could get messy as it allows for overlaps (eg. level 0-1, 
repeat_on 2;3) and other kinds of underspecified/undefined combinations (e.g. 
level 0;1, repeat_on 2;3).

Fortunately something that I haven't encountered in real-world data yet, but 
I'll better add a check for this in our implementation.

Regards,
Volker
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