[QGIS-Developer] Might snap change a 2D layer to 3D? discussion how to fix https://issues.qgis.org/issues/16927

[Luigi Pirelli]

Hi

next week I'll work on some 2.18 regressions [1] [2] [3] all regarding
issues related if a provider can or not manage an automatic geometry
type conversion.

One of them [1] is the fact that snapping a 2d layer to a 3d one, the
new feature become 3D, but the original layer remain 2d => error
during commit because incompatibility.

IMHO a solution should leave the snapping to modify 2D to 3D. The
reason is to allow user to rise up a flat vector if this is the user
intention (do you agree?)
some considerations:
1) IMHO if there is a single-2-multi type conversion have to be
notified via messageBar (do you agree?)
2) We can add a snapping option like "maintain geometry type" (True by
default) that avoid to change geom from 2d to 3d => raise exception as
soon as it happen (do you agree?) and not only at commit time (e.g.
when save changes)
3) add a generic check in the editing buffer that check geom
compatibility as soon as a geom is changed.

3) can be solved as stated here:
https://qgis.org/api/2.18/qgsvectorlayereditbuffer_8cpp_source.html#l00197
"// TODO: check compatible geometry"
in this place can be added the same controls set in commitChanges() of
the same class... or moved these controls in a reusable methods.
Would be great to have this control outside EditBuffed or as static
method and with SIP binding to allow other application to do this
check for their business functions.

any opinion?

Luigi Pirelli

p.s. these fixes can be applied to 3.x too

[1] https://issues.qgis.org/issues/16927
[2] https://issues.qgis.org/issues/16948
[3] https://issues.qgis.org/issues/15741

**************************************************************************************************
* Boundless QGIS Support/Development: lpirelli AT boundlessgeo DOT com
* LinkedIn: https://www.linkedin.com/in/luigipirelli
* Stackexchange: http://gis.stackexchange.com/users/19667/luigi-pirelli
* GitHub: https://github.com/luipir
* Mastering QGIS 2nd Edition:
* https://www.packtpub.com/big-data-and-business-intelligence/mastering-qgis-second-edition
**************************************************************************************************