topic Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh in Fusion Support Forum

Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

m.savazzi — Fri, 06 Apr 2018 15:24:42 GMT

I've followed the different video but I do get always an error on too many facets.

In this object I have 102916 facets: https://a360.co/2GDoYTV

Can you help me?

What am I doing wrong?

Also I could avoid to do the conversion if I would be able to project the mesh on a sketch but I've not found how to do it

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

jeff_strater — Fri, 06 Apr 2018 15:35:08 GMT

yes, your mesh has way too many facets. I think the limit is 20,000 for this conversion. What are you looking to do with this mesh? You mention projecting it to a sketch. Have you tried out the Mesh Section tool? This is not a project, but is a cross-section through your mesh - it's good for doing reverse engineering to re-create a BRep from mesh data. I'll post a video shortly.

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

TrippyLighting — Fri, 06 Apr 2018 15:40:34 GMT

After importing the mesh you need to change into the Model workspace and create a mesh section. I am wondering what you want to achieve with this though.

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

m.savazzi — Fri, 06 Apr 2018 15:42:15 GMT

My primary objective is to have it back as object to manipulate it and integrate it with other objects I'm doing.

I think that with 3d printing and STL objects this is a super common requirement and a major headache for everyone... it would be great to have Fusion to do it automatically 🙂

The process is not that difficult... either you convert to object,,, either you do the projection on surfaces

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

m.savazzi — Fri, 06 Apr 2018 15:47:47 GMT

that's coooool 🙂

a good step ahead!!!

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

jeff_strater — Fri, 06 Apr 2018 15:54:03 GMT

The screencast below is just a sample of the workflow. It's not clear exactly what you want to do with this mesh, but this will give a flavor of how you can use these commands to create sketches, which can then be used features such as Extrude, Revolve, Loft, etc to rebuild your model.

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

m.savazzi — Fri, 06 Apr 2018 16:13:26 GMT

It's a step ahead but on complex objects is a nightmare

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

TrippyLighting — Fri, 06 Apr 2018 16:16:19 GMT

The purpose of CAD is accuracy. If that would not be the case we'd all be using Sub-D mesh modeling software. In fact because of the low accuracy of 3D printing, Using Sub-D software to create models for 3D printing is very popular. No CAD needed in many cases.

Converting a .stl into a solid or surface model that represents the same accuracy as the original model cannot really be done. When that .stl is created fro the original model accuracy and fidelity and the mathematical representation of the model are lost. The reason is obvious. A mesh has a finite resolution whereas a CAD model is described by mathematical formula that are accurate to the limits of the computing hardware.

The second reason that people seem to not understand is that .stl files are fully triangulated meshes. The difference between a properly structured Sub-D model, a quad-mesh and a fully triangulated mesh is that the fully triangulated mesh does not have a topology (in the mathematical sense).

So when a .stl is created accuracy and topology are lost. They cannot be recreated fully automatically without human input.

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

m.savazzi — Fri, 06 Apr 2018 16:59:02 GMT

TrippyLighting

yes and no at the same time.

Yes you are correct on the degradation, on the lack of mathematical structure etc...

No because in any case the Mesh is a closed space, is an object, approximate but is an object, inside and outside. So it could and should be possible to create backward and object.

Then there are a lot of stuff the computer can do without humans that is to reconnect splitted surfaces, splitted line in one original line. Computer can recognize easily patterns to decide that a set of triangles is a circle etc...

Also surfaces can be reduced by F360, it is what is possible to do on the mesh with the Patch menu 🙂

The request is not to go form STL to the CAD design below but to be able to have something decent to start to work with... and I think this is doable. 🙂

In any case if you use tinkercad (from Autodesk) it allow to work on objects. what it lacks is to retro project them

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

TrippyLighting — Fri, 06 Apr 2018 18:11:13 GMT

@m.savazzi wrote:

TrippyLighting

No because in any case the Mesh is a closed space, is an object, approximate but is an object, inside and outside. So it could and should be possible to create backward and object.

That is not generally true and is also easily observable in your mesh, which is also not closed 😉

I think I've come to understand the subject of meshes fairy well in the almost 30 years I have worked with computer graphics, rendering, 3D modeling and CAD. I am fairly what can be done with computers and I am also keenly aware what other softwares are out there and how they approach this subject.

You are correct that "something" can be done, but that is why I started my response with "the purpose of CAD is accuracy". "Something" is usually not accurate. There is a lot of research going on in the area of re-creating NURBS/CAD data from meshes, predominantly from scanned mesh data with the aim to reverse engineer a given object. Reverse engineering is big business and that really drives this research. As such there are software solutions available that do this, e.g. 3D systems with their Geomagic Design X and Space Claim are some of the leading mid range software solutions aiming at this market segment. These software packages are magnitudes more expensive than Fusion 360.

Having all that said, the purpose of such solutions is definitely not to revers engineer Thingyverse Mesh Models that were created as .stl, which in days and low cost or even free CAD software is really quite hard to explain. Most of those models and I would go so far as to extend that to you model as well, don't need any automated conversion process, but are quite easy re-designed with native Fusion 360 tools.

I am not suggesting that your model is a Thingyverse model and while of clearly technical nature (rather than being an organic shape) is complex and will take some time to re-construct with native tools.

I am also not by any means suggesting that the following applies to your particular case, but based on vast and overwhelming experience on this forum I can say the the majority of such requests come from people very new to the matter the expect an easy button at zero cost.

Re: Issue converting STL - Mesh to BRep conversion - Projecting a Mesh

TrippyLighting — Fri, 06 Apr 2018 18:32:08 GMT

I've looked closer at this model and it is definitely NOT easy to redesign with native CAD tools. It can be done but it would be a lot of work.

Depending on what modifications you want to make Autodesk Meshmixer is a free but very powerful software package with the hole purpose of working with triangulated meshes. Working with it is quite different from working with a CAD model, but you might find that it is a good solution to solve your problem. IF you want to 3D print this object you'll have tp loose the mesh but I believe Meshmixer has a good toolset to do that and you won't have to convert your mesh first into "something" else. You can work directly with mesh data!