How do I mirror modelling on surface?

Hi. I have a half of a subD face that I'm working on. I mirror it and attach it. Now, is there a way I can model on one half and have the other half respond, even though its a whole surface? Basically I want half of the surface to be instanced.

thanks for your time
ktpr

Well you instance the half and do a neg scale on it but you have to hold offf on attaching it

use CPS(Connect Poly Shape) plugin

or, if you model with the poly/cage, instance the half, combine and merge/union the halves and sds the result (flip its interactivity off, and the sds too, and flip on the input halves). im going to tidy up a real light script for automating this and post it soonish. or, like beaker sais, use cps ...perhaps even kill the smoothing, and sds it instead, effectively using just its mirroring functions.