This is suprising indeed. Im my test using the v.out.postgis was still way faster than constructing with postgis topology (about x3 I think).
Are you using v.out.postgis -l, with grass 7? Grass is a topology that is more node centered, opposite to postgis topology which is more edge centered. It is possible to output a node centered topology with grass as text (*v.info <http://v.info> -t*), but I found it unpractical to try to convert this into a propoer postgis topology with pure SQL. Now I think I should have used a python way from within grass (grass offers full binding, so it should be doable to loop trough grass internal topology and convert it to postgis topology) I tried to reach grass dev several time to try to improve the postgis export, I had no answer. My intuition is that the slowness comes from the fact that grass tries to write edge by edge , and each time the edge_data trigger are triggered. The correct way would be to compute full topology structure, then deactivate trigger, then fill table , then reactivate trigger. Cheers, Rémi-C 2014-11-18 19:48 GMT+01:00 Sandro Santilli <[email protected]>: > On Wed, Nov 12, 2014 at 10:51:34AM +0100, Rémi Cura wrote: > > Note you could have directly exported into postgis topology, which is > slow > > but very convenient (stil faster than postgis topology conversion). > > I'm not a grass user, > > from what I understood you have to use the "-l" switch in the command " > > *v.out.postgis*" > > I'm trying this out today, and indeed is very slow, much slower than > building the topology, which is surprising to me. > > A look at database activity shows that the command (v.out.postgis -l) > is writing _simple_ features in the output layer. Do you have an idea > about how to skip that part ? (TopoGeometry would be enough for PostGIS > to reconstruct the SFS on demand). > > --strk; > > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >
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