[postgis-users] strange behaviour in PostGIS strictly below operator?

[Thijs van den Berg]

Excellent! 
Thanks for helping me understand, very clear. 

That makes me think there is no way around this, considering I want/need to use GIST indices to speedup these type of queries? If I did the following type of query (which *does* give the intended result) then it looks like it’s doing a full table scan instead of using the GIST.

SELECT ST_X(ST_PointFromText('POINT(2288605254 0)')) < ST_X(ST_PointFromText('POINT(2288605300 0)'));


> On 11 Aug 2017, at 16:03, Darafei Komяpa Praliaskouski <me at komzpa.net> wrote:
> 
> Hi! 
> 
> These are bbox operations, and IIRC they operate on float (32bit) bbox of geometry. I think conversion of point to bbox adds some epsilon around a point. 
> 
> пт, 11 авг. 2017 г. в 16:57, Thijs van den Berg <thijs at sitmo.com <mailto:thijs at sitmo.com>>:
> Hi All,
> 
> I'm getting some strange results that I can’t explain. Maybe some of you know whats going on?
> 
> I want to use PostGIS for spatial queries on scientific data (2d point sets). In the following query I want to select points to the left of some other point but it looks like there is some rounding going on? AFAIK the coordinates are stored as 64bit doubles and so this should be no problem?
> 
> This query gives TRUE as expected:
> SELECT ST_PointFromText('POINT(88605254 0)') << ST_PointFromText('POINT(88605300 0)’);
> 
> This query gives FALSE,the only difference is two leading 2’s in the X coordinate.
> SELECT ST_PointFromText('POINT(2288605254 0)') << ST_PointFromText('POINT(2288605300 0)');
> 
> 
> Below is my version info:
> SELECT PostGIS_full_version();
> POSTGIS="2.3.2 r15302" GEOS="3.5.1-CAPI-1.9.1 r4246" PROJ="Rel. 4.9.3, 15 August 2016" GDAL="GDAL 2.1.3, released 2017/20/01" LIBXML="2.9.4" LIBJSON="0.12.1” RASTER
> 
> Kind regards,
> Thijs
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