[postgis-devel] <<->>

Paul Ramsey pramsey at cleverelephant.ca
Fri May 22 11:17:53 PDT 2015

Yes, I think a special operator function that looks at the incoming geometry and chooses the right distance function, and interpolates the M values could be built out of the parts we have lying on the table.



On May 22, 2015 at 7:27:21 AM, Sandro Santilli (strk at keybit.net) wrote:
> 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;

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