Line offset Tool: Line disappears when offsetting in negative value direction

[PhilippPaeslack]

What is the bug or the crash?

With new Profile see short video

https://github.com/qgis/QGIS/assets/123968129/d5dd6f1d-9c21-4eb7-ac62-f74c4c3b45b6

Steps to reproduce the issue

With my profile and pc specs: 2024-06-17 at 18-15-56erwer.webm

Versions

QGIS-Version | 3.36.3-Maidenhead | QGIS-Codeversion | 2df96554 -- | -- | -- | -- Qt-Version | 5.15.13 Python-Version | 3.12.4 GDAL-Version | 3.9.0 PROJ-Version | 9.4.0 EPSG-Registraturdatenbankversion | v11.004 (2024-02-24) GEOS-Version | 3.12.2-CAPI-1.18.2 SQLite-Version | 3.45.1 PDAL-Version | 2.6.3 PostgreSQL-Client-Version | unknown SpatiaLite-Version | 5.1.0 QWT-Version | 6.2.0 QScintilla2-Version | 2.14.1 BS-Version | Windows 11 Version 2009   |   |   |   Aktive Python-Erweiterungen CalculateGeometry | 0.6.9 Generalizer3 | 1.0 HideDocks | 0.7.1 inspireatomclient | 0.8.1 layout_loader | 1.1 mmqgis | 2021.9.10 processing_saga_nextgen | 1.0.0 profiletool | 4.2.6 qfieldsync | v4.9.1 QGISSortAndNumber-master | 1.0 StyleLoadSave | 1.0 db_manager | 0.1.20 grassprovider | 2.12.99 MetaSearch | 0.3.6 processing | 2.12.99 CustomToolBar | 1.1 QGIS-Version 3.36.3-Maidenhead QGIS-Codeversion [2df96554](https://github.com/qgis/QGIS/commit/2df96554) Qt-Version 5.15.13 Python-Version 3.12.4 GDAL-Version 3.9.0 PROJ-Version 9.4.0 EPSG-Registraturdatenbankversion v11.004 (2024-02-24) GEOS-Version 3.12.2-CAPI-1.18.2 SQLite-Version 3.45.1 PDAL-Version 2.6.3 PostgreSQL-Client-Version unknown SpatiaLite-Version 5.1.0 QWT-Version 6.2.0 QScintilla2-Version 2.14.1 BS-Version Windows 11 Version 2009 Aktive Python-Erweiterungen CalculateGeometry 0.6.9 Generalizer3 1.0 HideDocks 0.7.1 inspireatomclient 0.8.1 layout_loader 1.1 mmqgis 2021.9.10 processing_saga_nextgen 1.0.0 profiletool 4.2.6 qfieldsync v4.9.1 QGISSortAndNumber-master 1.0 StyleLoadSave 1.0 db_manager 0.1.20 grassprovider 2.12.99 MetaSearch 0.3.6 processing 2.12.99 CustomToolBar 1.1 ### Supported QGIS version - [X] I'm running a supported QGIS version according to [the roadmap](https://www.qgis.org/en/site/getinvolved/development/roadmap.html#release-schedule). ### New profile - [X] I tried with a new [QGIS profile](https://docs.qgis.org/latest/en/docs/user_manual/introduction/qgis_configuration.html#working-with-user-profiles) ### Additional context _No response_

[agiudiceandrea]

@PhilippPaeslack, thanks for reporting. I cannot replicate the described behaviour using QGIS 3.36.3 on Windows 10.

https://github.com/qgis/QGIS/assets/16253859/6b3f5784-ed86-4334-92c8-a7836fe7f1a0

Please provide a sample project and layer and exact steps in order to replicate the issue.

[PhilippPaeslack]

offset tool bug.zip

You find the Project attached. I found out that this only happens with Lines that consist of more than 2 Points. When i remove all points but 2 it works again.

[agiudiceandrea]

@PhilippPaeslack, it seems to me the issue doesn't occur on my Windows 10 system using both QGIS 3.38.0 and QGIS 3.34.8 with the provided project and layer:

https://github.com/qgis/QGIS/assets/16253859/3c6216b1-e843-40b2-b4f1-0a7082f31160

Have you actually tried if the issue occurs also using a new QGIS user profile as indicated in the issue report?

Please provide detailed steps to replicate the issue.

[agiudiceandrea]

@PhilippPaeslack, I've managed to replicate the issue on my system. It only occurs for some lines, after actually applying a negative offset to the line, but not during the offset preview.

When the Offset Curves tool fails, the following warnings are displayed:

2024-06-28T08:45:40     WARNING    Map tool offset curve : The feature cannot be modified because the resulting geometry would be empty
2024-06-28T08:45:40     WARNING    Map tool offset curve : The feature cannot be modified because the resulting geometry would be empty

[PhilippPaeslack]

Thanks a lot for your effort. Yes, for me this also only happens when actually applying the offset to the line, the preview works. Why is the resulting geometry empty? Does this mean that there is some error in my data structure? Why does this happen only if there are more than two junctions in the line?

[baswein]

It seems like vertex 46 on the large polygon has some sort of issue. The offset preview also has a gap at that vertex. See GIF. If I move the vertex slightly the negative offset works fine. Not sure if this is a geometry error (fix geometries does not fix this) or if it an issue with the offset tool. Running Merge lines creates a polygon that doesn't disappear but creates a gap like in the preview.