[Qgis-psc] GEOS discussions

[Sandro Santilli]

On Tue, May 26, 2015 at 01:04:32AM +0200, Tim Sutton wrote:

> > For the M values support he made a PR which I'm esitant to merge due to
> > its effect of growing every coordinate used by GEOS by 30%. A compile-time
> > define to enable/disable it would make it easily acceptable.
> 
> 
> I guess the issue with this is that we will need to ask upstream packages to enable this flag for different distros in order for us to be able to use the geometry checking tools in QGIS….which means that there will be anyway a 30% overhead added…..or we need to bundle in our own copy of the geo lib into the QGIS source tree with the correct flags enabled which also isn’t great. Is there anyway to make it a run time switch rather than a compile time switch? Seems like that would solve a lot of issues.

Yes, there would be a way to do that. Would also _reduce_ memory usage
for 2D-only inputs. We don't know how would that affect CPU load.
I'd love to see an implementation and some benchmarks with it.
Best discussed on the PR

 https://github.com/libgeos/libgeos/pull/45

--strk;