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notice, this text has been added to the reference manual where up-to-date documentation should be maintained:

https://developer.blender.org/diffusion/BM/browse/trunk/blender_docs/manual/modeling/modifiers/deform/surface_deform.rst

Surface Deform Modifier

The Surface Deform Modifier allows an arbitrary mesh[note] surface to control the deformation of another, essentially transferring its motion/deformation. One great use for this is to have a proxy mesh for cloth simulation, which will in turn drive the motion of your final and more detailed mesh, which would otherwise not be suitable for simulation. (Brief technical documentation)

Options

SDef UI.png

Target 
The object to which to bind. (This setting is unavailable after binding)
Interpolation falloff 
How much a vertex bound to one face of the target will be affected by the surrounding faces. This essentially controls how smooth the deformations are. Note that while lower values result in smoother deformations, they may also introduce slight artifacts. (This setting is unavailable after binding)
Bind 
Bind the current state of the modified mesh to the current state of the target mesh, such that any later change in the target mesh will deform the modified mesh as well. Note that until the bind has been executed, this modifier will have no effect whatsoever. (This does not affect the target object)
Unbind 
Once the mesh is bound, the Bind button changes to Unbind. Executing this frees the modified mesh from the target, and resets it its original shape. (This does not affect the target object)

Notes

  • The meshes are bound with regard to global coordinates, but later transformations on the objects are ignored. This means that one can freely transform the target or modified object after binding, without affecting the modified object. The modified mesh will only pick up changes to the target object's mesh itself.
  • The further a mesh deviates from the target mesh surface, the more likely it is to get undesirable artifacts. This is an inherent characteristic of surface binding in general, so it is recommended to have reasonably well matching meshes, in order to get a good bind.

Target Mesh Validity

While there are no restrictions with regard to the modified mesh, the target object's mesh has a few constraints, which if not followed, will prevent a successful bind. The target mesh has to follow these conditions:

  • Must not contain edges with more than two faces.
  • Must not contain concave faces.
  • Must not contain overlapping vertices (doubles).
  • Must not contain faces with collinear edges.

Here is a handy reference of what is and isn't valid:

SDef MeshValidity2.png SDef MeshValidity1.png

Demo

SDef demo.gif

A detailed mesh with blue thingies, bound to a simplified mesh with a cloth simulation.