Form to a surface

[LeonMF]

I had to drop in here to lob off a question but I'm stumped on this one.

The use case:

I want to fit a an item around a surface.  A good example of the type of thing I'd ike to do is the 3D printed cast:

http://www.wired.com/wp-content/uploads/blogs/design/wp-content/uploads/2013/07/cast1.jpg

So, I've got a 3D scan of an object which I've reduced to 5000 points and converted to a BREP.  Originally, I thought I could place a cylinder around my object and use the pull command.  Unfortunately, the large number of faces results in unpredictable results.  So, I was able to get some good results by creating a cylinder body and using combine with cut to create a perfect fit to my surface.  I can then use the scuplt tools to shape my object.

However, I'd like to start with something that is fit to the surface of my object.  Ideally, I'd like to create a shell of a small (1mm) thickness around my object that I could then work on with the sculpt tools to refine my shape.

I'm sure I'm missing something obvious and I'd appreciate any help.

Thanks!

[brucehuang]

Hi, thanks for your post here. 

Currently, I know there's a TSpline modeling command in Fusion can do some limited work about this. It's under "CREATE" toolbar group. There's an "Object Snap" option. Once it's toggled, then the new TSpline face's vertices will be snapped onto the reference object (normally it's a stl surface). You can also specify an offset for the snapping. 

 

Hope this helps, and happy new year.

Bruce (Fusion Development)

[deyop · Accepted solution]

You can probably get better performance by using the mesh directly instead of converting to BRep.  The conversion takes each mesh facet and makes a single BRep face out of it which is expensive when using the Pull or Object Snapping commands in the Sculpt workspace.  You may not need to reduce it to so low a face count if you work directly with the mesh.

Here is an overview of some of the techniques that can be useful when fitting to a target surface, either mesh or BRep.  Keep in mind the target surface cannot be a T-Spline so when you do need to fit to a T-Spline you may want to convert to BRep.  This may also be a reasonable time to use Direct Modeling instead of Parametric Timeline until you have a form you are satisfied with.  The reason for this would be the ability to mix BRep and T-Spline bodies in the same environment.  

Snap Vertices to Objects tutorial

I did a similar approach with this leg form for a prosthetic.  I have provided a link to the data below so you can download it as an example.  If you are trying a more complex "skin" then you may want to build the individual T-Spline faces on the mesh with the Face command with Object Snapping turned on.  Another point to keep in mind is that the  Object Snapping of vertices actually places the controls on the target, not the surface itself so you have to adjust for this offset either through an offset value  when snapping or using Interpolation when you have finished all of the snapping.  The Pull command will actually place the surface points on the target which is preferable.  Get the cylinder as close as possible initially and then Subdivide to create more vertices for snapping.  The more vertices the closer the match.

Link to LegForm

This Object Snapping process is not ideal for converting captured forms into usable parts but currently is the best alternative.  We are working on a number of projects to simplify this process.

Let us know if you have further questions.

Thanks

[LeonMF]

I had tried playing with this command but, either my skills are too rudimentary or it is a far too tedious process to use.  I wasn't able to make something work but I will go try again.

[LeonMF]

The reason I had to convert to brep is that I couldn't figure out how to scale a mesh and Fusion 360 imports my meshes at 10X size so my workflow is to convert to brep and then shrink the brep.  I'd love to skip that step.

I will review your techniques and see what I can utilize.

Thank you!

Leon

[deyop]

Are you importing the mesh as an STL or OBJ?  If so you will see an option for setting the units to those that were used to create the input mesh file.  This should address the difference in scale.  Here is another posting that may help explain.

You can also select the Scale command in the Model - Modify dropdown.  Mesh is a valid input and will allow you to scale to the required size.  You may want to explicitly set the scaling point so you know where the scaling originates.

Thanks

[LeonMF]

I've been using the upload mesh from the data panel.  Using insert mesh results in the same scaling problem, even when I select mm.  The model is dimensionally accurate except for being scaled 10X.

I misspoke earlier when I said I couldn't scale the mesh.  I can do that.  I was having trouble selecting and moving the mesh once I enabled timeline.  I suspect using the create form or base feature mesh insert method will resolve that issue.

[dunderhead]

The scaling problems you're encountering may be this:

 BUG: fix STL import scaling and translation,

see my comment there for a possible work-around. As for obtaining a nice grid like the one shown below, here's how I do it:

• Delineate the outer most face, using the face command (single, snap) that'll contain a single T-spine patch (with no funny business, no star points) -- you'll have to think about the eventual u-v mapping, that is your isocurves or countour lines or what you like to call them
• Select the face, then edit form, and select the "vertex" box in Selection Filter; then window select the whole face again, so that all 12 "grips" or tangent handles -- they are red -- become selected-- by now a yellow link symbol, saying Link tangent handle will appear; press the yellow symbol (this is to overcome the problem described in  Subdivide, insert edge, ... create strange folding artefacts near outer edge, which may eventually result in self-intersecting surfaces)
• Now, subdivide your 1x1 patch using the default 2x2 setting  -- again with snapping
• Select all the four faces and apply the subdivide command again, still snapping
• And, again, select all faces, now sixteen, and subdivide
• Repeat until satisfied
• And as *only* the final step, select the grid, and use "pull" in surface mode

Any deviation from this recipe (using "pull" too soon, not recursively subdividing, or not deleting the tangent handles) may result in ill-formed meshes, possibly with self-intersecting folds or other ugly stuff! The resulting T-splines mesh is by no means perfect, but you can of course decide yourself where to subdivide it further for handling detail. The trick is again to avoid pull-to-surface until the last moment because it induces much lateral movement of the vertices.