[postgis-users] PostGIS layer spatial tolerance

[Picavet Vincent]

Hi,

> I come from the ESRI and Oracle world. Both ArcSDE and Oracle 
> Spatial have user-defined spatial tolerance for each 
> spatially enabled layer. This ensures that coordinates are 
> exact, down to the last decimal (or integer for ArcSDE). 
> I cannot find in the documentation or in the functionality 
> that PostGIS has an awareness of spatial tolerance. What I 
> can find is:
> "All floating point comparisons within the SQL-MM 
> implementation are performed to a specified tolerance, currently 1E-8"
> but nothing about actual storage.

A solution in order to take spatial tolerance into account, despite not being automated, would be to systematically use the st_snaptogrid postgis function when creating or modifying geometries.

http://postgis.refractions.net/docs/ST_SnapToGrid.html

If you want a certain level of automation of this process, you should consider writing a trigger which snaps geometries to a specified grid on insert or update.

This is probably better than rounding coordinate in the application code.

Regards,
Vincent

>  
> For me, the easiest solution would be to use a spatial 
> tolerance. Otherwise, we may need to round all coordinates in 
> the application code to e.g. 14 valid digits.
>  
> Best Regards
>  
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> Andreas Oxenstierna
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