Split parts on MultiLineString: discards data #21997
Labels
Bug
Either a bug report, or a bug fix. Let's hope for the latter!
Digitizing
Related to feature digitizing map tools or functionality
Milestone
Author Name: Mike Taves (Mike Taves)
Original Redmine Issue: 13983
Affected QGIS version: 2.12.0
Redmine category:digitising
The issue is that geometry data is silently discarded when using the Split Parts tool on MultiLineString geometries with QGIS 2.12.1-Lyon (16760fd).
Consider a simple MultiLineString in a PostGIS database: @MULTILINESTRING((0 0, 10 0))@
Editing the geometry with the Split Parts tool (in the Advanced Digitizing toolbar), e.g., to split the line in the middle will do this: keep only the MultiLineString from the start to the split location, and discard the MultiLineString from the split location to the end, such as @MULTILINESTRING((0 0, 5 0))@.
An expected result would be something like @MULTILINESTRING((0 0, 5 0), (5 0, 10 0))@.
A second experiment with @MULTILINESTRING((0 0, 5 0), (5 0, 10 0))@ will show data loss of other parts that were not split. Splitting the first part will keep the line from the start to the split location, and will discard both the remaining portion of the first part, and all of the second part, so result is @MULTILINESTRING((0 0, 2.5 0))@. Furthermore, splitting the second part will discard all of the first part, and keep only the start of the second part to the split location, so result is @MULTILINESTRING((5 0, 7.5 0))@.
An expected result would keep the other parts of the geometry, as well as the new parts that were split, so either @MULTILINESTRING((0 0, 2.5 0), (2.5 0, 5 0), (5 0, 10 0))@ or @MULTILINESTRING((0 0, 5 0), (5 0, 7.5 0), (7.5 0, 10 0))@.
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