[postgis-devel] <<->>

[Sandro Santilli]

On Fri, May 22, 2015 at 05:28:18AM -0700, Paul Ramsey wrote:

> > > - I could hack something up, that would fuse a true 2d or 3d
> > > distance with a centroid-based distance for the M dimension
> 
> In this case, for a 4D object I’d get the 3d distance, square it, add the square of the distance of the M dimension from centroid to centroid, and sqrt that. So “kinda” like what you’d get if you ran an actual 4d distance.
> 
> > > - I could have a hybrid that does centroid distance for 3dm and 3dzm
> > > but true distance for 2d and 3dz.
> 
> This would do full centroid distance (for all dimensions) for some cases, and real distance (for all supported dimensions) for others. 

Could option 1 be further tweaked to use the the M values of
the closest 3D (or 2D) points rather than the centroids.
I think the distance function (at least the 3d one) is already
based on finding the "closest points".

--strk;