Converting Blended Surfaces To Solids in Fusion 360?

[sohnrog]

Hello Guys and Gals,

I have a project I'm working on that involves CT scan data.  I use a program called Osirix to generate a 3D surface model from CT scans.  The data can be exported into .iv, .obj, .stl, .rib, and .vrml.  I have been able to import the .obj and .stl files.  I am able to see the surface model, but I can't seem to do any operations on the surface.  

I'd like to be able to convert the surface to a solid and then cut and modify as if it were a regular part file.  I have read some of deyo's comments that converting a surface of trangles to T-splines is not an easy task.  I was hoping someone could help me with this conversion.  I am using a Mac, but I have access to a PC if there were some free conversion software.  I've added a sceenshot so you can see what I'm working on.

Thanks!

Roger 

[jakefowler]

Here's the resultant bunny, BTW 😉

[sohnrog]

Hello All,

Thanks a lot to Trippy Lighting.  That screencast was awesome and I owe you a huge thanks.  I was able to get the obj into fusion and convert it, but it still appears to be a surface model only.

1.  How to convert it to a solid body?

2.  What I'm really trying to accomplish is to cut the bone (humerus) at the anatomic neck.  I have placed a construction plane at the level I want to cut the head.  I also have an axis down the shaft of the bone.  However, for my research project, I need to be able to rotate the cutting plane on the shaft axis by 10 degree increments and cut the head again at each respective angle.

3.  The final result for my research will be to determine the volume of material that is in the dome of cut bone for each varied angle of cut. Any way to determine the volume of material in fusion?

Here's the link to my fusion model to download:  http://a360.co/1SlLvlP

Thanks so much for all your help so far.

Roger Sohn

[sohnrog]

To clarify what I"m trying to accomplish, I've attached a couple pictures of what we do in surgery.  We cut the humeral head with a guide that is attached to a post that is down the shaft of the humerus shaft.  We can vary the angle of our cut by rotating the cutting guide around the post and then we pin the guide in place and cut the bone.  I'm not sure how to get a construction plane to behave like the cutting guide does when we rotate the guide on the post.  

I hope some of this makes sense.

Please feel free to ask for clarification.

Roger

[TrippyLighting]

OK, here's wht I'd do.

1. Upload the .obj file to the cloud using the data panel in fusion 360

2. Open the file in Fusion 360 and convert. This converts the mesh into a T-Spline. This is the purple symbol listed in "Bodies".

3. This is optional, but you can actually delete the originl mesh, whcihis the orange sybol in "Bodies"

4. Save and close the file.

5. Insert the file into a new design using "Insert in currnt design" You'll be skae to savethe currnt design before it lows you to insert the bone file.

The bone will now be inserted as a linked component ( not a body) into the current design. Familiarize yourelf with the difference betwen a body and a component. You'll want your bone to be a component going forward.

Go to "Learing->Function->Build Assembies->Bodies and components"

6. Right click on theat new component and break the link.

7. Save the file.

Now in this new file you will by default also record the timeline, which will allow you to change feaures more easlily.

7. Create your construction planes as desired to intrsect with the bone.

8. You can simply sketch a big block on one of the contruction planes and use the "Modify->Combine" tool to use the big block as a cutting tool. 

[Anonymous]

Hi Roger, very cool system (although I get a little queasy thinking about stuff like that).  I cut the bone body you shared by going in Model workspace to Modify > Split Body and choosing the construction plane as the splitting tool. 

For calculating volume right click on the desired resulting body in the browser tree and go to Properties. 

Just for future reference, as I stated before you can just directly convert a mesh into a Brep body in the Create Base Feature mode, provided under 10,000 faces, without needing to convert the faces to quads. 

Good luck!

Jesse

[Anonymous]

Of course the conversion to quad faces then importing as Tspline results in a nicer non-faceted surface, so what you did is probably a good idea if you're looking for that high quality appearance.

Jesse

[sohnrog]

Hello All,

Thanks again on all your help with this research project.  I have had a lot of fun with this process so far, but it seems like the scale of the final model is off.  I don't know where the scale is being changed, but I suspect it might be with Meshmixer.  Others on the Meshmixer forum have complained about scale issues.  Is there a way to insure the accuracy from one program to the next?  

My workflow is this:  

1. Osirix tranforms CT scans into 3D surface model (stl).  

2.  Import stl file into Meshmixer and smooth the surface --->save as obj file.  

3.  Import smoothed stl into Blender and remesh into quad faces with lower octree value to reduce number of faces --> output ojb file.  

4.  Import Obj file into Fusion 360 and do my analysis.

The scale is off by about 10% in the 3 samples I have run so far.  Please feel free to chime in if you have a solution.

Thanks!

Roger

[jakefowler]

Hi Roger,

Is there any chance you could share the original STL?

The translation workflow you described doesn't sound like it would cause the kind of issues you are seeing: translation issues tend to result in large changes in scale (due to units mismatching) like 10x difference - rarely anything on the scale of ~10%. Do you think it's possible that the smoothing operation in Meshmixer is reducing the volume? If you export the smoothed OBJ after step 2 directly into Fusion, how does it look?

One other culprit could be the remeshing in Blender, although I haven't seen such issues with this workflow. Did you try using Memento's quad export for this step?

BTW - we're working right now on adding Meshmixer-like tools directly into Fusion - let me know if you'd be interested in giving us feedback on the functionality we're working on.

Thanks,

Jake

[sohnrog]

Here's the original file.  

Thanks so much for your help!

https://dl.dropboxusercontent.com/u/94424269/humerus%20without%20ostps.stl

[sohnrog]

Hi Jake,

Yes.  I would love to give feedback on the new functionality you are testing.  Let me know how I can be involved.

The smoothing function in meshmixer should shrink the model but I'm noticing an increase in the model.  I measure 52mm diameter of the humeral head on CT scan.  It has grown to about 65mm by the time it is a model in fusion.  Does meshmixer automatically adjust the scale when importing stl files?

I have run 3 separate bone samples for data.  2 of the models seem to be pretty close to the original measurements.  It's just the 1 sample that seems to be too big.  I need to be able to figure out where the error crept in before I run all of my samples.  

I noticed that when remeshing in blender, there is a button for "scale" that is defaulted to 0.900 (right next to octree depth).  I suspect this is a problem.  I tried changing it to 1, but it only goes to 0.990.  Could that be the issue?  It seems like it would make the model too small, and I'm seeing a model that's too big...

I didn't try memento, but I will give it a try if necessary.  I'm trying to keep the workflow as simple as possible.

Thanks again.

Roger

[sohnrog]

Ok.  I think I figured it out.  I eliminated blender altogether and accomplished the quad mesh transformation using Memento.  It was much simpler and allowed me to reduce the number of faces.  No scaling issues now.  Thank you all for your help.  I look forward to seeing these tools brought into fusion some day.

[jakefowler]

Glad that helped! And thanks for sharing the STL.

Our aim obviously is to make the workflow even smoother (and results better) inside Fusion. Will be in touch about that 🙂

Jake

[qforms]

In last week or two, when I trying insert quad mesh in sculpt mode, it insert as triangulate mesh like I insert mesh in model mode.

[TrippyLighting]

Yes, we know.

Did you read the entire thread and are there still equations on how to resolve this issue ?

[sohnrog]

Hello. It's me, the OP. I've been having good reaults with the steps outlined by grippy lighting. However, I have recently had some hiccups. I use mesh mixer to smooth the model. Next, I import into blender and reduce the faces using remesh at octree level 5 or 6. It defaults to a scale of 0.9, so I increase it to 0.99 (the maximum allowed) then I export as obj file. When I import the file into fusion, the scale is off in some models. It seems to be a 10x distortion. I'm trying to identify where the error gets introduced. I was wondering if anyone can help troubleshoot. I suspect it's the blender remesh step that's the problem but I can't figure it out. I also previously was able to use memento as an alternative but it's no longer freeware. Any help is appreciated.

[TrippyLighting]

Try Instantmeshes. I's very fast as well!

[sohnrog]

I was able to download the free version of remake (formerly memento).  However, the scaling issue persists.  Now I"m starting to suspect the issue is in Fusion 360's import because the scaling problem happens with both blender and remake.  I've attached a link to a screencast.  I appreciate your help.  

<iframe width="560" height="315" src="https://www.youtube.com/embed/odtaAqfhJVI" frameborder="0" allowfullscreen></iframe>

If it's possible to rescale in Fusion 360, that might be my second choice, but I worry about introducing error in case the scaling issue is not exactly 10x.

[sohnrog]

Never mind. This is not the problem. See my next post.

[sohnrog]

Here's a screen cast of the issue.  It seems like I can insert the mesh without any scale issues.  However, if I actually go to upload the obj file from the cloud, the 10X scale issue happens every time.

[jakefowler · Accepted solution]

Hi @sohnrog,

This looks likely to be a cm/mm mismatch. Our cloud translators use cm as base units when the data doesn't contain units information, but ReMake uses mm by default. So I would strongly suspect that this resulting in an exact 10x scale.

There are a couple of ways to handle this:

• Instead of importing the OBJ through the data panel, create a new design and use the Insert Mesh tool to insert the OBJ. This will give you a dropdown to choose the import units. If the OBJ was exported from ReMake using millimeters, and you choose millimeters from the Units dropdown in this command, the model should come in at the expected scale.
• Alternatively, you can change the units in ReMake before Export. In Model Settings > Set scale and units, switch to cm and scale by 10%. The model should now be the same physical size, but represented as cm. Now when you export from ReMake and import through the Fusion 360 data panel, it should be imported at the correct scale. 

Let us know if these didn't work for you. Our long term plan is to provide units settings and other options when importing models through the data panel, which should make this easier; but for now hopefully one of these two will work for you.

Thanks,

Jake