[postgis-users] MultiPoint to CircularString to LineString

[Denis Rouzaud]

Hi all,

I spend some time to convert a MultiPoint geometry to a circularString 
then to a LineString (since qgis does not handle circularstring). I 
achieved this by extracting all coordinates from the MultiPoint, then 
concatenating them into a CircularString and finally convert it to a 
Linestring. Here is the sql:

     SELECT 
ST_CurveToLine(ST_GeomFromText('CIRCULARSTRING('||left(tsum(ST_X(ST_GeometryN(wkb_geometry,n))||' 
'||ST_Y(ST_GeometryN(wkb_geometry,n))||','),-1)||')'),12) AS wkb_geometry
     FROM   mytable
     CROSS JOIN generate_series(1,100) n
     WHERE n <= ST_NumGeometries(wkb_geometry)
     GROUP BY id;

where tsum is an aggregate:

CREATE AGGREGATE distribution.tsum ( BASETYPE = text, SFUNC = textcat, 
STYPE = text, INITCOND = '' );

I use this sql in a view(ie I have my multipoint table, and my 
linestring view).
This apparently works but when I load the layers in qgis I have a 
postgis error for the view: ERROR: current transaction is aborted, 
connands ignored until end of transaction block.

So, here are my two questions:
1. Does someone know why I have an error in qgis?
2. Does someone have a smarter/better idea to create a curved linestring 
from a multipoint?

The whole SQL code to create table and view is here 
https://github.com/3nids/qWat/blob/a281ccaccfb0e246d9753f075b1a85f46c4a4eea/sql/dimension.sql

Thanks a lot!!!

Denis






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