(Forwarding to PG User lisdt thread as well) Good news - overlaying the full dataset works using JTS OverlayNG in Snap-Rounding mode. It completes in 195 s using a grid size of 1e-8 (which is quite fine).
Interestingly it didn't complete when using OverlayNG with Snapping noding (which is heuristic-based noding strategy intended to preserve more precision). I'll have to look into that further. Here's some instructions on how to run this in JTS: - Clone the branch https://github.com/dr-jts/jts/tree/overlay-sr - Build using maven clean install - Run the TestBuilder ( https://github.com/locationtech/jts/blob/master/doc/JTSTestBuilder.md) - Convert the SQL file to a WKB file by removing the SQL header and footer, leaving only the WKB text - Drop the WKB file onto the TestBuilder A input box to load it - Run the geometry function OverlayNG/union with Grid Scale = 100000000 On Tue, Jul 7, 2020 at 10:49 PM Jonathan Schultz <[email protected]> wrote: > 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 <[email protected] > <mailto:[email protected]>> 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. > > > > > > > >
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