[QGIS-Developer] PSA: do NOT build QGIS with libspatialindex >= 2.0

[Raymond Nijssen]

Hi! Today I upgraded to Ubuntu 26.04 which ships with libspatialindex 
2.1 and could not compile QGIS. For anyone running into the same 
problem, you can set the compile option WITH_INTERNAL_SPATIALINDEX=ON 
and use the libspatialindex 2.0 shipped with QGIS.

https://github.com/qgis/QGIS/commit/0b1ba631b36dc6903f3dcdf7ffe3970cdedab4dd

Raymond


On 9/16/25 02:39, Nyall Dawson via QGIS-Developer wrote:
> 
> 
> On Tue, 16 Sept 2025 at 10:37, Nyall Dawson <nyall.dawson at gmail.com 
> <mailto:nyall.dawson at gmail.com>> wrote:
> 
>     Hi list,
> 
>     While tracking down the failures from https://github.com/qgis/QGIS/
>     pull/63180 <https://github.com/qgis/QGIS/pull/63180>, it's revealed
>     that using QGIS with libspatialindex >= 2.0 gives completely
>     misleading results for nearest neighbour geometry searches.
> 
>     The root cause is an optimisation from the upstream library
>     (https://github.com/libspatialindex/libspatialindex/
>     commit/6fe9ff769243579ed74f7f27409dd1dda6591634 <https://github.com/
>     libspatialindex/libspatialindex/
>     commit/6fe9ff769243579ed74f7f27409dd1dda6591634>) that breaks how
>     downstream clients could previously implement custom nearest
>     neighbour comparators. From my research I don't think this is
>     fixable in QGIS, and will need an upstream fix.
> 
> 
> Sorry -- to clarify, that should have been >= 2.1 . 2.0 did not include 
> the offending commit.
> 
> Nyall
> 
> 
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