[QGIS-Developer] Split parts tool creates invalid polygons

[Anita Graser]

Hi,

The split parts tool creates invalid polygons according to GEOS check
validity. This issue seems to have been discussed two years ago
https://issues.qgis.org/issues/12799 but it still persists today in master.

To reproduce:
1. Create a memory layer with multipolygon type
2. Add a polygon
3. Split the polygon using split parts
4. Use the vertex tool to move the parts apart, in order to avoid issues
with polygon parts sharing an edge or vertex
5. Run check validity

Method GEOS returns 1 invalid:

{'ERROR_COUNT': 0, 'ERROR_OUTPUT':
'output_bd77440a_35eb_4f60_8273_3e4be16349f1', 'INVALID_COUNT': 1,
'INVALID_OUTPUT': 'output_3e1922d6_dc3d_40e1_a0a3_6becbd5cbeb3',
'VALID_COUNT': 0, 'VALID_OUTPUT':
'output_ba297216_4997_4b0d_accd_b1669ff038a5'}

Method QGIS returns
​ 1 valid​
:

{'ERROR_COUNT': 0, 'ERROR_OUTPUT':
'output_9feeaeb9_569b_40e8_9062_ad7bd411472d', 'INVALID_COUNT': 0,
'INVALID_OUTPUT': 'output_b6b99e1e_1bbe_442f_8864_99d334efdf45',
'VALID_COUNT': 1, 'VALID_OUTPUT':
'output_0a7d2f97_4bcc_40c1_806e_ad0ff73bcd05'}

The attribute table
​ of GEOS' invalid output layer does not provide any information on the
type of error.

Should I reopen the ticket? I don't see how this tool can be used without
ruining the features.

Regards,
Anita
​
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