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<TITLE>RE: [postgis-devel] More work on Cascade Union</TITLE>
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<P><FONT SIZE=2>>It's annoying that there's so much overhead in all the marshalling that<BR>
> goes on between Postgres, PostGIS, and GEOS. Points are the worst case<BR>
> for this, since they have so much overhead relative to their size. I'm<BR>
> not sure what the best approach is to mitigate this. One option might<BR>
> be to do more point operations directly in PostGIS, since they tend to<BR>
> be fairly simple compared to more complex geoms. But this starts<BR>
> getting into a lot of code to be developed...<BR>
<BR>
Perhaps its just my ineptness at understanding C-code and more specifically how all these pieces fit together, but regarding the marshalling seems in the unite_garray<BR>
there is a lot of wasted time<BR>
<BR>
1) pull a geometry out of PG_LWGEOM<BR>
2) convert pulled geometry to PostGIS2GEOS<BR>
3) Union with our GEOS result<BR>
4) copy our new GEOS result to g2<BR>
5) destroy our old result<BR>
6) rebuild new result by taking g2 and unioning with next PostGIS2GEOS<BR>
<BR>
---<BR>
<BR>
Would seem much more efficient to just marshall the whole array to some sort of GEOS array or Geometrycollection<BR>
do our busy work with the GEOS array/collection all in GEOS land<BR>
then return back a GEOS result which we then convert to GEOS2POSTGIS.<BR>
Looking at the JTS code - it seems to be doing that - working against the full set of lines and points in a collection rather than this busy back and forth stuff. I see GEOS code that seems to do that too (work with a collection)<BR>
<BR>
Thanks,<BR>
Regina<BR>
<BR>
<BR>
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