[Expression] point_n function should be coherent with other vertex based functions and algorithms

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 21282
Affected QGIS version: 3.7(master)
Redmine category:expressions

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I don't know if I should report it as a bug or a feature request...

The point_n function returns a specific node on a geometry, based on the provided index. The first vertex index is 1.
But when using Processing to extract vertices from a feature, the vertex_index is 0-based. Some other expression that manipulates vertices (angle_at_vertex, distance_to_vertex) are also 0-based.
It could be nice to align the point_n function with the others.

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Related issue(s): #29102 (relates)
Redmine related issue(s): 21284

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[qgib]

Author Name: Harrissou Santanna (@DelazJ)

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• relates was configured as [Expression] Allow negative value for vertex index in angle_at_vertex/distance_at_vertex/point_n... functions #29102

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)

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IMHO, it's an inconsistency which should be considered as a bug. Fixing this will have to wait until we cross the QGIS 4.0 bridge.

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• regression was configured as 0
• crashes_corrupts_data was configured as 0
• version was configured as 3.7(master)
• tracker_id was changed from 2 to 1

[Pedro-Murteira]

@DelazJ Hello, is this issue still valid on recent releases?

[github-actions]

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[github-actions]

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[DelazJ]

Still an issue and according to @nirvn comment above it has to wait for 4.0. So unless it has been reported on a 4.0 breaking changes repository, it shouldn't be closed.

[Koyaani]

geometry_n and interior_ring_n are not really vertex based functions, but their index start from 1.