[Qgis-developer] new dependency on GEOS C++ library

Sandro Mani manisandro at gmail.com
Thu Oct 1 04:39:37 PDT 2015

On 01.10.2015 11:47, Sandro Santilli wrote:
> I've found that qgis is now dependent on the C++ GEOS API,
> due to the new src/core/geosextra.
> It seems to me that the "geosextra" code in its current incarnation
> only exposes a function to basically round coordinates to a precision
> grid, but in no way changes the precision of operations performed by
> further GEOS functions on the resulting geometries.
> This is discussed in detail in https://trac.osgeo.org/geos/ticket/713
> So my question is: if grid-snapping is enough for QGIS use, is adding
> a new dependency on GEOS really needed, or isn't there other internal
> code for doing coordinates editing work (would seem easy with Qt
> standard library?).
As resulted from the discussion in the geos ticket: the goal is having 
the operations run in reduced precision, not just merely snap to grid. 
The discussion revealed however that snap to grid is basically what ends 
up being done with the current implementation, due to a 
mis-understanding of mine of the geos internals. As suggested in the 
geos ticket, I'd like to fix this to work as initially intended, and 
keep geosextra in QGIS until a new release of GEOS comes out which 
implements needed changes in the C-API.
> As I've been asked to help with getting the code in place for what
> I've understood are good new functionalities I'm here to better
> understsand the issue, why the new code is needed and how to best have
> it available, considering also that latest GEOS release was published
> on August 15, 2015.
> See also https://github.com/qgis/qgis/pull/2302
> --strk;

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