[postgis-users] More details for errors

Denis Rouzaud denis.rouzaud at gmail.com
Tue Mar 27 07:50:56 PDT 2012

Yes, it is 2.0

Well, I am turning around the problem...
I have to do a cast, as I used 
in the first view to prevent errors of unconnected lines.

Right now the best solution I have is to let the view being unusable, 
and another view to report errors.
This is not very satisfying as if a problem occurs, I cannot use my view 
until I fix the geometric errors.

Basically, I need to compute a view with a LineMerge returning 
LineString (i.e. leaving away features leading to MultiLineString) and 
another view returning IDs of features leading to MULTI.

I thought about using ST_Touches but it only uses two geometries and I 
can have more in the LineMerge. No idea what to look for...

Thanks for your help. I could go deeper in the problem!



On 03/27/2012 04:39 PM, Nicolas Ribot wrote:
> On 27 March 2012 16:09, Denis Rouzaud<denis.rouzaud at gmail.com>  wrote:
>> Hi Nicolas,
>> Thanks again.
>> Well, this working, but this not performant...
>> Based on your suggestion, I tried this:
>> in view1:
>> ST_Multi(ST_LineMerge(ST_Union(wkb_geometry)))::geometry(MultiLineString,21781)
>> AS wkb_geometry
>> Then in view2:
>> ST_CollectionHomogenize(wkb_geometry)::geometry(LineString,21781) AS
>> wkb_geometry
>> FROM view1
>>   WHERE ST_NumGeometries(wkb_geometry) = 1;
>> And I can detect problems by doing:
>> SELECT id FROM view1  WHERE ST_NumGeometries(wkb_geometry) != 1;
>> But this is slowing down a lot.
>> I think that the ST_CollectionHomogenize is not the right way. Is there a
>> better function to transform multiline to line if I am sure I only have
>> lines?
> I did not know this function. 2.0 ?
> You can simply do:
> st_setsrid(ST_geometryN(wkb_geometry), 21781) AS
> wkb_geometry
> FROM view1
>   WHERE ST_NumGeometries(wkb_geometry) = 1;
> If geoms come from linemerge, no need to cast to a linestring. It is
> already one.
> Nicolas
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