ST_SetM, ST_SetZ, (ST_SetX, ST_SetY?) functions

[komzpa]

I have a multipoint that I'd like to assign M to before ST_Collect'ing it with other multipoints and pushing into ST_GeometricMedian.

I see no way to do it without complete deconstruction of geometry into sets of x/y coordinates and building them back with ST_MakePoint with an extra argument.

It would be cool to have ST_SetM (and in other cases ST_SetZ) that will allow getting Z/M value for all objects in geometry from some other calculation/column.

[dbaston]

Could ST_GeometricMedian be made into a multi-column aggregate function, instead of abusing the M ordinate?

This seems like a useful addition regardless.

[komzpa]

This is actually doable via ST_Force3D / ST_Force4D optional arguments now.