[postgis-users] Re: two different geometries with the same Astext

[Miguel de la Fuente]

On 7/23/05, strk at refractions.net <strk at refractions.net> wrote:
> Miguel, if the summirized test still holds:
> 
> > >        1) within: false
> > >        2) within(dropbbox): true
> > >        3) within(addbbox(dropbbox)): true
> 
> I'd like to have some confirmation of the fact that
> the boxes in 1) and 3) differ.
> 
> Try something like:
> 
>        select box2d(dropbbox(g2))::geometry::text = box2d(g2)::geometry::text;

This returns false

>        select box2d(dropbbox(g1))::geometry::text = box2d(g1)::geometry::text;

and this returns true

> 
> I'd expect one (or both) these to return FALSE.
> 
> --strk;
> 

I ran this:

select astext(g1), box2d(g1), box2d(dropbbox(g1)),
          astext(g2), box2d(g2), box2d(dropbbox(g2))
from table1

And select by hand the minimum and maximum from the astext() result
for comparing and get

(5256301.4  6014697.56,  5256369.25  6014741.46)  g1
(5256301     6014697.5  , 5256369.5   6014741.5 )  box2d(g1)
(5256301     6014697.5  , 5256369.5   6014741.5 )  box2d(dropbbox(g1))

(5256301.4  6014563.13, 5256456.23  6014741.46)  g2
(5256301.5  6014563    , 5256456       6014741.5 )  box2d(g2)
(5256301     6014563    , 5256456.5    6014741.5 )  box2d(dropbbox(g2))

As you see the box2d is rounding, and box2d(g1) is not inside box2d(g2).
I can't understand why.