[postgis-users] Help with ST_CLIP

Simon SPDBA Greener simon at spdba.com.au
Fri Mar 12 15:13:09 PST 2021


 > So I don't work with rasters and will defer to others on any specifics.

Agreed which is why I hit this list.

> I think I would try to make a simplistic test case with a little 
> raster and a little polygon, that you can play with to figure out the 
> write set of commands and data types that work.
Yeah, fair enough.
> The only reasons I can think of that you results are all null are:
> 1) the polygon does not intersect the raster, because of types, 
> projections whatever
> 2) maybe a code bug
> 3) some obscure usage error that is not well documented

Yeah, all these are possible. I tended to think that it was a projection 
issue causing the two objects not to interact, but I converted the grid 
cells to polygons (ST_DumpAsPolygons) and they align with the park 
boundary I am using.

I converted everything to 3857 with ST_SummaryStats of an ST_Clip still 
return all NULL values.

> I know you know this stuff pretty well, so if you can not sort it out 
> with a test case, at least you'll have that to submit with a bug 
> report or have something that other experts can try out and maybe 
> correct.

Well I don't really! Yes, I have the standard familiarity that comes 
with a Geomatics degree, and some basic experience but I too am not an 



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