Shrink wrap and retopo problems

[inge_xsi]

I've been struggling trying to retopo high resolution geometry in XSI using the shrink wrap method suggested in several threads on XSIBase and CGTalk.

Yes, I can shrink wrap a grid to the high res surface but the problem is that when I then try to translate a point, face, etc... using the tweak tool I get crazy results. What do I mean by that? Well, simply that when I attempt to translate the object that has been shrink wrapped it will not move as expected... it behaves in a crazy manner. Like I try and move it and it seems to scale or attempt to move in a direction other than the way that I'm moving my mouse... I don't get it.

I've tried the various other options available in the shrink wrap operator such as along normal, to closest surface, etc and no joy, it does not want to behave.

Any ideas what it going on here? I would simply expect the object that has been shrink wrapped to the surface to stick and then to allow me to move the points along the surface in a predictable manner but that simply isn't happening.

I don't get it.

Any clue what I've done wrong?

Inge

[Projectghost2501]

i know this may be insulting your intelligence so please don't take offence if you have or haven't tried this stuff but have you tried freezing the model once you've applied the shrink wrap? or you could try setting neutral pose on the mesh that has the shrink wrap applied to it. Also you might be in the wrong translation type selected (view, COG, Global, Local, etc). Also make sure you don't have any animation lying around on there as that may have an effect.

Like i said this is probably stuff you've tried but thought i'd throw in my 2 cents ^^

[inge_xsi]

i know this may be insulting your intelligence so please don't take offence if you have or haven't tried this stuff but have you tried freezing the model once you've applied the shrink wrap? or you could try setting neutral pose on the mesh that has the shrink wrap applied to it. Also you might be in the wrong translation type selected (view, COG, Global, Local, etc). Also make sure you don't have any animation lying around on there as that may have an effect.

Like i said this is probably stuff you've tried but thought i'd throw in my 2 cents ^^


Hi,

Nope you are not offending me or insulting my intelligence in anyway, after all if I was smarter then this would be working for me.

Well, let me outline what I am doing....

1. brought in a high res obj file into XSI, about 250K polygons, open manifold.

2. After import it was pretty huge, so I scaled it down to a more reasonable size, roughly 3 SI units.

3. Rotated the mesh so that it faced the proper direction in the view ports.

4. Froze all transforms - mesh now zeroed out.

5. created a polygon grid, rotated it 90 degrees, translated it out so that it would be just slightly in front of my mesh.

6. Selected the grid, froze all transforms, nice and zeroed out.

7. With grid selected, switched to shape animation construction mode.

8. Deform>Shrinkwrap and picked high resmesh and then ended pick session.

9. Tried several options, nearly all seemed to create havoc with the grid with the exception of follow normals; so I will go with that.

10. Switch modeling construction mode.

11. Enable tweak tool (note I am working in the perspective view) in the "view" mode (not cog, not local, etc.)

12. Try to move some points.... and whoa.... it is crazy weird. First off there is lag but when stuff starts moving it is simply crazy. The grid acts like it's made of springs, if I move a single point other points surrounding it try and compensate in some way. If I move a point some of the others seem to scale or translate in strange or unpredictable ways.

Oh and NO... before you ask I do not have the proportional tool enabled.

BTW - I have no animation or other keys set or stored.

I've got no idea why this is happening but it seems like some kind of a bug. Perhaps the shrink wrap op does not like large meshes or perhaps the fact that it's an open manifold mesh is making it act crazy.

I will have to test this with a closed, watertight mesh to see if that makes any difference but if anyone has any further ideas... well, that would be great because I can't make this work at all.

Thanks.

Inge

[grahamef]

Ah... an imported mesh. They can sometimes cause problems.

Try the techniques here: http://softimage.wiki.avid.com/index.php/Cleaning_up_Imported_Meshes

[inge_xsi]

Ah... an imported mesh. They can sometimes cause problems.

Try the techniques here: http://softimage.wiki.avid.com/index.php/Cleaning_up_Imported_Meshes


Yes, imported mesh but despite that fact the problem still persists even after trying as suggested on the wiki.

From the looks of things it appears that something is not quite right with the shrink wrap operator.

BTW - I tried testing this with a standard primitive sphere and guess what, I get similar results so something is wacked. Try it yourself and see. Create a poly sphere and up the res in the UV directions and then follow the steps that I posted previously.

Oddly, you will notice that if you press the m key and then try to translate a point (note that I said translate) that not only do you obtain translation but also rotation... WTF?
Why on earth are points rotating (when rotation is not enabled)? If I look at the rotation values in the MCP when I move a point they are giong all over the place... too weird.

Anyway, as far as I can tell something is not right with this.

Still, I'm hoping that someone else can repro or suggest a remedy.

Fingers crossed.

Inge

[grahamef]

OK, I think I see what you're getting. If you mute the Shrinkwrap operator you can see why it's doing what it's doing. The cumulative effect of all the MoveComponent operators on the grid has changed the directions of the vertex normals, so then they get projected in different directions when Shrinkwrap is set to Follow Vertex Normals further up the stack.

This doesn't happen with other options. I don't know why Closest Surface and Closest Surface (Smoothed) aren't giving you good results. They always work well for me.

One thing you can try, in Secondary Shape mode before you shrinkwrap, is to select all the points and scale down to zero in local Y (press Ctrl when dragging the manipulator and you will snap at 0.5 then 0). This will flatten the grid before shrinkwrapping but after moving the points in the Modeling region.

[mantom]

Check your transform mode when activating the translate tool. Translating subcomponents will behave differently depending on which mode you have active.

Deform by surface is a perfect example. If you surface deform a grid onto a NURBS surface, then translating points in local mode will move the grid's points in the coordinate space of the surface deformer, not the grid. X translation is along the NURBS surface's U direction, Z translation is along the NURBS surface's V direction, and Y translation is along the deforming surface's normal. If you change to other transform modes (view, for example), then the rules will change to be based on the camera's pov or the grid's transform.

In any event, play around with the various modes and you'll hit on one that works to your liking.

TIPS:
- Play around with using COG and REF modes.

- Check out the transform preferences as there are additional options to modify subcomponents as a group or individually - which can be drastically different depending on what you're doing.

- Pay attention to where operators lie in your construction history. translating points is typically a modeling operation whereas the shrinkwrap operator usually resides in the animation portion of the construction history - in other words, the shrinkwrap is evaluated AFTER the movecomponent operators generated from moving points. therefore, you may want to set construction history to secondary shape mode to ensure translations are evaluated after the shrinkwrap.

Matt

[bblevins]

You may want to check out Topogun, its meant to do exactly what your trying to do with shrinkwrap. Its very easy to use.

http://www.topogun.com/

[Black104]

When ever i encounter problems like that i click on the "snap" tool.
Try Using the snap functions set to face or point. - Once your done just click it off and contunue retopoing.

Hope this helps.