[postgis-users] PostGIS topology ISO SQL/MM complete
strk at keybit.net
Mon Oct 17 05:35:12 PDT 2011
On Mon, Oct 17, 2011 at 01:11:14PM +0200, José Carlos Martínez Llario wrote:
> I think many people were waiting for a persistent topology model.
Luckly someone also made something about it ! :)
> There is already some performance bechmark comparing the simple
> feature model with the persistent topology model about quering,
> writing topo geometries, etc. specially talking about face
It really depends on the kind of query.
If you were to find adiacent faces or points-in-polygon
it's straightforward to query a topological model (those relations
are explicit). If you need to _build_ a simple geometry starting
from the components it'll take more time. This is currently your
only option for renderers only supporting simple geometries, but could
change by making renderers aware of TopoGeometry. Still you'll usually
need to fetch multiple rows to build a single geometry (ie: multiple
edges for a single face). But you can always see simple geometries as
some form of "cache" for fast access and keep it updated on underlying
topology change. This is currently already possible with pgsql machinery.
I suggest you test it yourself  based you _your_ use case.
But anyway topology is more for sanity (normalized spatial data)
 it'll be easier with the toTopoGeometry function:
() Free GIS & Flash consultant/developer
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