[postgis-users] Question on topology

[Neumann, Andreas]

Hi Sandro, 

I let this function run during the night and after 7.5h I got an error
message: 

------------------------------------ 

ERROR: Corrupted topology: adjacent edges 159972 and -159958 bind
different face (0 and 78697)
CONTEXT: SQL statement "SELECT topology.ST_AddEdgeModFace(atopology,
snode_id, enode_id, rec.geom)"
PL/pgSQL function st_createtopogeo(character varying,geometry) line 153
at PERFORM
********** Error ********** 

ERROR: Corrupted topology: adjacent edges 159972 and -159958 bind
different face (0 and 78697)
SQL state: XX000
Context: SQL statement "SELECT topology.ST_AddEdgeModFace(atopology,
snode_id, enode_id, rec.geom)"
PL/pgSQL function st_createtopogeo(character varying,geometry) line 153
at PERFORM 

------------------------------------- 

I have to say that I did not tune Postgis memory-wise - maybe I should
do that next. But the above error message probably doesn't indicate a
memory problem, but a problem with the data. 

My data: 2582 polygons with a total of 167176 vertices. 

I am now also following alternative approaches. I found a software that
provides me with the edges - and now I have to find out which landcover
polygon is left and which is right of the edge. I got a working query,
but still quite slow. I will write a separate mail about this query. 

Andreas 

On 2016-07-11 19:32, Sandro Santilli wrote:

> On Mon, Jul 11, 2016 at 04:52:40PM +0200, Neumann, Andreas wrote:
> 
>> The ST_CreateTopoGeo() function runs for a very long time. >45 minutes
>> on this relatively small dataset. Did I use the wrong combination of
>> functions at the top, or is it a problem that after ST_CurveToLine() my
>> data contains a lot of vertices? 
>> 
>> My total dataset has 75'000 polygons, so I fear that, unless I did a
>> erroneous combination of the functions, that the ST_CreateTopoGeo() may
>> be too slow for my purpose? How big where the datasets that you used so
>> far with Postgis topology? I hope it is a mistake on my side.
> 
> Topology loading is known to be slow, and there's been work toward drafting
> ideas to speed it up. What could help is very data-specific, but some things
> are common to all datasets, like keeping the number of vertices below a given
> threshold (ST_Subdivide can help). None of those heuristics are currently
> implemented in ST_CreateTopoGeo, but you could find strategies yourself
> using the TopoGeo_addLinestring function, passing it each split portion of
> each polygon boundary in desceding geometry order (which helps with getting
> polygon holes be included before polgon shells).
> 
> There are some load times on the rttopo wiki (but it's in italian):
> https://git.osgeo.org/gogs/rttopo/librttopo/wiki/ItProfilazioneUcsRt
> 
> According to those numbers:
> 
> - a Xeon E31245 (3,30Ghz) with 24GB Ram
> could load 840'143 polygons with a total of 47'254'882 vertices
> in about 3 days (250'518 seconds) using PostGIS master.
> 
> - an i7-4750HQ (2.00Ghz) with 16GB Ram
> could load 16,757 polygons with a total of 794,020 vertices in
> about 1 hour and 13 minutes.
> 
> Depending on the distribution of your polygons (how many bounding box
> overlaps) your number may be better or worst.
> 
> I recommend doing the loading in separate transaction chunks, so that
> you can look at the topology as its being built and more importantly you don't
> end up loosing all the work shall an exception arise.
> 
> --strk;

  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20160712/e8c4a795/attachment.html>