[postgis-users] How to get the centroid of an bounding box using st_extent

[Charlie Savage]

Hi Martin,

> Charlie, this is not a problem.  Floating point rounding error only 
> comes into play when you are doing computations using numeric 
> operations.  Extent computation only uses comparison operations, and 
> these are exact.

Ah - that's interesting.

   So if a BBox is computed for a geometry and it has the
> max and min x and y being exactly the same, it can be determined to be a 
> Point, with no worry about error.  (Conversely, if a geometry is not a 
> point, it must have at least two coordinates with different Xs or Ys, 
> and so its BBox will have a non-zero extent.

Thanks for the information.  Ok, then I'll see if I can fix up the bbox2 
  to geometry conversion so it returns a point if either xmin=xmax or 
ymin=ymax.  Currently it returns an invalid polygon - same problem that 
envelope had.

Charlie
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