Use Subdivison when drawing new topology on top of exiting geo?

Is there a way to draw topology on top of existing geometry and and to have subdivision levels available for that secondary layer of geometry?

In this little exercise I have first rougly fleshed out the overall volume of the tool, then I used the Retopo tool to lay out some of the topological details (the raw volume mesh is set to almost completely transparent here). At some point a preview of the smoothed mesh would be extremely  helpful – that way one could massage the vertices of the retopo mesh closer to the desired shape. When using SubD levels however the Retopo tool stops working here.


The non-subdivided secondary layer


With SubD preview on – at this state one can no longer use the background constraint to drag the mesh vertices into position.


The idea here is not to get an as low poly mesh as possible – with this second layer I rather would like to create a second Hi Res mesh, one which not only has the desired outer shape, but also the required topology to hold the detail. Note that I don't actually work on that particular part, it's rather a general problem I'd like to solve.

Here's the file, in case you want to have a look.

Is there a way to draw topology on top of existing geometry and and to have subdivision levels available for that secondary layer of geometry?

Works Ok for me using Andrei's interface.

- Turn on retopo and specify which existing geometry you want to retopo over
- Draw some new polygons on existing geometry with retopo on
- Turn on Sub'd for the new polygons
- Extrude or move edges of new polygons

Hmm,
in subdivided state and with Retopo on (which turns on the background constraint) I can not use any of the functions of the actual Retopo command (Common Modeling Shortcut Tools > Retopo). Can you?
 
While I'm sure that it didn't work yesterday I can now use the normal tweak command to drag vertices around and als extrude via the normal edge extrusion command. But this only applies for certain regions of the model. Can you edit along the symmetry plane? No avail here...

Hi Polyxo

I only did a simple test of creating a sphere and making it the retopo reference object. I then created some polygons on that sphere using retopo commands and subdividing it. I continued to tweak verts, extrude edges on those polygons while subdivided and it all works well. I just tried symmetry and that works fine also.

I should say, that most people who retopo objects do that in the unsubdivided state though. Of course you turn subd on and off to check how things are looking.

Kevjon,
thanks again for testing. It's interesting that you did not run into issues with your own test, but the last gif I posted hopefully demonstrates that there clearly is a problem. You could try it out yourself with the file I shared.

I should say, that most people who retopo objects do that in the unsubdivided state though.

The word Retopo is misleading in this context. I used the Retopo workflow to create new, more complex geometry with an existing volume as the guide for the outer shape. For this purpose useing SubD was very helpful. I explained this in my first post – but I'd be glad to learn about an elegant alternative way to do this.