building:part with the same position as the building gives a false warning

[Nadjita]

What steps will reproduce the problem?

1. Draw the outline of a building
2. Draw a building:part=yes outline using the same nodes as the building
3. Add more building:part=yes ways to the building
4. Upload

What is the expected result?

No warning-message, because a lot of houses only have 1 or 2 dormers and no outbuildings whatsoever.

What happens instead?

A warning "ways with same position" pops up

Please provide any additional information below. Attach a screenshot if possible.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2022-08-29 16:59:00 +0200 (Mon, 29 Aug 2022)
Revision:18543
Build-Date:2022-08-30 01:30:57
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (18543 en) Linux Freedesktop.org 21.08.15 (Flatpak runtime)
Memory Usage: 1314 MB / 3944 MB (627 MB allocated, but free)
Java version: 17.0.1+12, Flathub, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.nimbus.NimbusLookAndFeel
Screen: :0.0 1920×1200 (scaling 1.00×1.00) :0.1 1920×1200 (scaling 1.00×1.00)
Maximum Screen Size: 1920×1200
Best cursor sizes: 16×16→16×16, 32×32→32×32
Environment variable LANG: en_US.utf8
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_US
Numbers with default locale: 1234567890 -> 1234567890
Desktop environment: KDE
VM arguments: [-Djosm.restart=true, -Djava.net.useSystemProxies=true, -Dawt.useSystemAAFontSettings=on]
Dataset consistency test: No problems found

Plugins:
+ CommandLine (35978)
+ OpeningHoursEditor (35924)
+ PicLayer (1.0.2)
+ RoadSigns (36011)
+ ShapeTools (1250)
+ SimplifyArea (35978)
+ buildings_tools (36011)
+ easypresets (1623509627)
+ terracer (35978)
+ turnrestrictions (36011)
+ utilsplugin2 (36011)

Tagging presets:
+ <josm.pref>/EasyPresets.xml
+ https://josm.openstreetmap.de/josmfile?page=Presets/Crafts&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Presets/contact(socialnetworks_IMs)&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Presets/Healthcare&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Presets/pedestrian_crossings_in_DE&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Presets/public_bookcase&zip=1
+ https://osmtools.de/josm/steps.xml
+ https://raw.githubusercontent.com/yopaseopor/traffic_signs_preset_JOSM/master/DE.zip
+ https://josm.openstreetmap.de/josmfile?page=Presets/Wikidata&zip=1

Map paint styles:
- https://josm.openstreetmap.de/josmfile?page=Styles/Enhanced_Lane_and_Road_Attributes&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Lane_and_Road_Attributes&zip=1
+ https://raw.githubusercontent.com/yopaseopor/traffic_signs_style_JOSM/master/DE.zip
+ https://josm.openstreetmap.de/josmfile?page=Styles/Coloured_buildings&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Styles/Maxspeed&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Styles/LitObjects&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Styles/BesideTheRoad_Speed&zip=1
+ https://josm.openstreetmap.de/josmfile?page=Styles/SidewalksAndFootways&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/SimpleBuildingTags&zip=1
+ ${HOME}/Sync/josm-styles/marks-buildings.mapcss
+ ${HOME}/Sync/josm-styles/landuses.mapcss
- https://josm.openstreetmap.de/josmfile?page=Styles/TreeCrownDiameter&zip=1

[Nadjita]

Example building with error message

[Klumbumbus]

Please add an example .osm file.

[Nadjita]

Example .osm file where validator is showing this error

[Nadjita]

Attachment added

[skyper]

There might be cases where building=* and building:part=* have to be "ways with same position", e.g. a building with a smaller level in the middle, but the example is wrong as the two building:part=* should not overlap.

[Nadjita]

I disagree in the two parts not having to overlap (structure-wise, the half-hipped roof covers the full roof and the dormer sits on top of it), but the point is that the warning is wrong, because a building and a building part can be "ways with same position" and it's not even uncommon. Even when disagreeing with my example.

[Tordanik]

Just to back up Nadjita's report: With 3D mapping, it is common for ways to have the same 2D location. This should not produce a warning.

And although the example file could be improved (e.g. by adding a min_height to the dormer so that it only starts above the wall of the larger building part), it is perfectly suitable for reproducing the problem.

[Hufkratzer]

This warning is also shown if one maps two closed ways with the same nodes but

• one with leisure=pitch, the other with barrier=fence or
• one with leisure=pitch, the other with building=roof.

It is not wrong to do that, it is better than to map only one way with all these tags together, compare

• ​https://lists.openstreetmap.org/pipermail/tagging/2022-May/064699.html
• ​https://wiki.openstreetmap.org/wiki/Tag:leisure=pitch#Covered_and_indoor_pitches

Maybe the rule should only produce a warning if both ways have the same tags.

[skyper]

I think the best solution for these cases is to use a multipolygon relation for (one of) the area(s).

[Hufkratzer]

This kind of use of multipolygons really requires a lot of prior knowledge and brain power that probably only a minority are willing to invest. As an illustration, I refer to the recent changeset discussion ​https://www.openstreetmap.org/changeset/131395070 (5th and 6th comment).

[Emvee]

I did check barrier=fence/hedge + landuse/leisure/amenity=* for NL and fixing some of these I also get "Ways with the same position".

I also think using a multipolygon for this is a almost always a bad solution, it makes things too complex. I guess it will even trigger a warning like multipolygon with only one member.