[postgis-devel] Trying to get st_convexhull to return a bonduing box for a collection of linestrings

[dave.potts at pinan.co.uk]

Hi

I have postgis table which includes a series of Linestrings, I am trying to create a single geometry that includes only the outside layer of line strings.

An example would be if the line strings described digital 8, formed from squares two boxes, I would want something looked like a rectangle, 

I have tried things like 

 select st_convexhull( st_union(st_startpoint(the_geom),st_endpoint(the_geom))) from bar_table

I assumed that I would get a polygon with the middle bar removed, what I got was a collection of linestrings

Has anybody got any suggestions?

regards
Dave.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-devel/attachments/20160103/6b0dd21c/attachment.html>