[postgis-users] st_equals strangeness

[Mark Cave-Ayland]

Paul Ramsey wrote:

> More to the point, it's a float32 box, not a double64 box. Your two
> points are in fact different, waaaaaay down deep into the precision of
> their 64-bit double coordinates. So deep in fact that the human
> readable decimal representations don't show it (look at the hexewkb
> output, and you'll see the differences, you should be able to do that,
> points are small enough to eyeball in hex).
> 
> So when the 32-bit box is extracted from the 64-bit doubles, the
> points are identical at that level of precision and = returns true,
> while st_equals working against the doubles does not.
> 
> P

Again, another demonstration as to why BOX2DFLOAT4s should never be used 
for calculations and only for internal "within" checks :(


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
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