[postgis-users] Topology precision

Marc-Antoine Nüssli nuessli.ma at gmail.com
Fri Jul 6 02:25:16 PDT 2018

Hi there,

First, I want to say a big thanks to Sandro Santilli and all people who
work on the topology features. It looks like it becomes now mature enough
to be used for production applications and this is really great to manage
geo-data much more consistently than with simple geometries (especially
when you deal a lot with territorial partitions like in my case)

I have a question regarding the precision value that we have to provide
when creating a topology. I am not sure to understand its purpose.
Somehow, I would have expected that it would be used when computing new
nodes positions, for example resulting from an intersection, but from my
tests it seems it is not the case (see my example below)
Do you have some links or other infos that would describe how & when this
global topology precision parameter is used?

Thanks in advance for your help!

Best regards,
Marc-Antoine Nüssli

Example with a simple self-intersecting linestring which yield a fuill
precision intersection node (without considering the topology precision

select createtopology('topo',-1,.01);
select topogeo_addlinestring('topo', 'LINESTRING(8.5 33.5, 14.9 37.4, 9.2
35.8, 11.6 32.9)', .01);
select st_astext(geom) from topo.node

"POINT(8.5 33.5)"
"POINT(10.230659025788 34.5546203438395)" --> computed intersection node
(with too much precision)
"POINT(11.6 32.9)"
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