[geos-devel] Exposing PrecisionModel, GeometryPrecisionReducer in the C API

Sandro Mani manisandro at gmail.com
Wed Jan 7 04:23:29 PST 2015

On 07.01.2015 13:19, Sandro Santilli wrote:
> On Wed, Jan 07, 2015 at 01:16:09PM +0100, Sandro Mani wrote:
>> On 07.01.2015 13:09, Sandro Santilli wrote:
>>> Changing the PrecisionModel of a Geometry is really needed
>>> to change the behavior of GEOS operations themselves. This
>>> is the kind of "exposure" I'd be interested to.
>> Yes I agree.
>>> Once you convert GEOS geometries to QgsGeometry you don't
>>> really care about what PrecisionModel is recorded in them,
>>> do you ?
>> I'm not sure, what are the implications if a pass back a
>> GEOSGeometry to QgsGeometry which has a fixed precision model, and
>> not the double model as is default?
> I don't know as I didn't read the QGIS code, but I know in PostGIS
> we scan coordinates of each point and copy them so the input
> PrecisionModel does not affect the conversion in any way.
> Even if you used WKT, the worst that could happen is that
> you'd get less decimal digits, but that's the real precision
> of the input anyway, so nothing is lost.
I could check in the code, but do you know off the top of your head 
whether GEOS can perform operations with geometries of different 
precision, i.e. say an intersection?
> --strk;
>    ()   Free GIS & Flash consultant/developer
>    /\   http://strk.keybit.net/services.html
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