[postgis-users] st_union produces different result from st_memunion

[Jonathan Schultz]

Oh sorry about that. Here is a link to the file on my own VPS: http://barraqda.org/dbca_dump_116_35_117_34.zip

I've been playing with JTS but it's a bit of a steep learning curve. Getting stuck on Java NoClassDefFoundError messages, I presume related to incompatible versions and such-like. I'd very much appreciate advice on running OverlayNG.

Cheers,
Jonathan

On 8/7/20 1:41 pm, Martin Davis wrote:
> That's interesting that ST_SnapToGrid doesn't help for the full dataset - but not totally surprising, since it's a pretty blunt instrument.
> 
> I'd like to try out the larger dataset.  That free download website seems to have a bunch of unpleasant strings attached though - is there any other way you can make the data available?
> 
> If you are able to run Java, by all means try OverlayNG.  Happy to provide advice on how to run it if needed.
> 
> cheers - Martin
> 
> On Tue, Jul 7, 2020 at 8:10 PM Jonathan Schultz <jonathan at schultz.la <mailto:jonathan at schultz.la>> wrote:
> 
>     Thank you for the prompt feedback.
> 
>     As you suggested I tried using ST_SnapToGrid and that worked very well even with a very fine grid - st_snaptogrid(geometry,0.000000000001). However when it came to a collection of lines more useful for real work (13540 records compared with 6 in the minimal dataset) I found that snapping even to a grid so coarse as to render the data useless - st_snaptogrid(geometry,0.01) - still produced an incorrect result.
> 
>     Here is the dump of my larger dataset: https://anonfiles.com/rdYcG1Edo2/dbca_dump_116_35_117_34_sql
> 
>     I'll have a go myself with OverlayNG.
> 
>     And I will file a PostGIS issue depending on the conclusions from this discussion.
> 
> 
>