(*
ERROR_METRIC.sml

Seth Porter <symmetry>

Signature for an abstract error metric which
can be updated by a merging operation when
two vertices are merged.

examples are Garland's quadrics, and Ronfard & Rossignac's
sets of planes
*)

signature ERROR_METRIC =
sig

    structure Geometry : GEOMETRY

    type metric

    (* point sequence (of length three) defines a plane, which
       determines a metric over space *)
    val init : Geometry.Point.point Sequence.seq -> metric

    val zero : metric
    val plus : metric * metric -> metric

    val evaluate : metric * Geometry.Point.point -> Geometry.Number.t
    val optimal : metric -> Geometry.Point.point option
    val toString : metric -> string
	
end