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Asked: 2026-06-05T02:02:28+00:00

I try to understand how does overlapping box with infinity works Why does the

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I try to understand how does overlapping box with infinity works

Why does the following exemple doesn’t work. It works fine except when i try to introduce two infinite values.

This exemple should return true.

SELECT box '((1,1),(infinity, 1))' && box '((2, 1),(infinity, 1))' AS overlap;
overlap 
---------
f

The two exemples below works

SELECT box '((1,1),(4, 1))' && box '((2, 1),(infinity, 1))' AS overlap;
overlap 
---------
t


SELECT box '((1,1),(4, 1))' && box '((2, 1),(5, 1))' AS overlap;
overlap
---------
t

So my question is : Is there something i’m doing wrong or that i don’t understand?

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1 Answer

  1. Editorial Team

    I asked on the postgresql buglist:

    Tom lane gave me this answer :

    The test for this involves

    FPge(box1->high.x, box2->high.x)

    where FPge is defined as 

    #define FPge(A,B)    ((B) - (A) <= EPSILON)

    When both high.x values are infinity, you have infinity minus infinity,
    which yields NaN in IEEE arithmetic, so the comparison to epsilon comes
    out false.

    In general I don’t think we promise that geometric operations involving
    infinite endpoints will behave sanely. There are probably a boatload
    of corner cases besides this one that’d need to be fixed before we
    could consider that a supported case.

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