[postgis-devel] <<->>

[Sandro Santilli]

On Thu, May 21, 2015 at 11:15:25AM -0700, Paul Ramsey wrote:
> I'm looking at converting this operator to do "true" KNN, just like
> <-> now does (for PgSQL 9.5).  A couple things hold me back:
> 
> - having to renovate the regression tests to handle testing both pre-
> and post-9.5 behaviors conditionally (yuck!)

You could have both expected files as different ones and set the
correct one in place at ./configure time.

Having two different operators for bounding box and real distance could
be a minor problem, if possible. BTW, can the 9.5 "recheck" capability
also be used to change && to be a _real_ overlap operator ? If it can,
would it make sense from a user point of view to change the behavior so
drastically ?

> - the lack of a "true" distance4d function to apply in the case of
> GeometryZM and GeometryM inputs. We have support for 2d, and 3dz
> inputs, but nothing for others.

Yep.
Defining an ND distance function for anything but points is pretty hard.

>   - I could hack something up, that would fuse a true 2d or 3d
> distance with a centroid-based distance for the M dimension
>   - I could have a hybrid that does centroid distance for 3dm and 3dzm
> but true distance for 2d and 3dz.
>   - I could do nothing and leave the <<->> operator as it is now

It'd be nice to get real-3D distance for 3DZ inputs.
But I don't get the difference between first and second options.

--strk;

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