Opening Mesh File Formats in Alibre Design

A prospective customer put this question to me today:

It has been great trying to use SYCODE software to import 3DS files from ArchiCAD to Alibre. I would love to work with both platforms more interconnected. Do you have a suggestion of how I could do that? I plan to use Alibre Design for my structural working shop floor steel fabrication details for units designed with ArchiCAD. I know Telka is great for this, but so is its price. More information will be greatly appreciated.

While we do not have an ArchiCAD to Alibre Design bridge, there is something else I would like to mention about opening mesh formats like 3DS into Alibre Design. We often receive support requests on this issue. So I decided to write my thoughts here on this blog for the benefit of others trying to do the same thing.

Here is the thing. Alibre Design is a solid modeling system. It does not have a mesh data structure. Neither does it have a mesh visualization structure like SolidWorks or Pro/ENGINEER. That’s why our Alibre Design add-ons that import mesh formats like 3D Studio (3DS), Wavefront (OBJ), SketchUp (SKP), Stereolithography (STL) and Visualization Toolkit (VTK) need to cough up solid models from the mesh objects described in these mesh files. So this task is not a simple conversion from one data structure in one format to another data structure in another format, which is what happens say in the case of importing a STEP file into Alibre Design. The task involves creating a trimmed planar NURBS surface for each triangle/quad of the mesh and then stitching them together to yield a closed solid or an open surface.

Maybe I should explain this by means of an example. Assume that we have a simple solid model of a sphere stored in a STEP file. The solid model contains just one closed spherical surface. Alibre Design’s STEP file importer simply reads the spherical surface stored in the STEP file and converts into a spherical surface in Alibre Design. However, the same sphere in a 3DS file would be stored as a mesh object consisting of maybe 200 triangular faces depending on the resolution selected when saving the 3DS file. So our 3DS importer add-on for Alibre Design needs to create 200 planar surfaces, trim them and stitch them together into a solid. This takes a lot of computing resources as well as time.

In fact, the time required increases exponentially with the number of faces to create, trim and stitch. So if you have a huge mesh containing thousands of faces, you are going to end up staring at a progress bar that appears to be stuck up. In reality the add-on is working overtime. The Task Manager will verify that.

So my advice to anyone trying to open a mesh format into Alibre Design (or for that matter, any other solid modeling system) is to try and break down the mesh into parts if possible. Unfortunately, in the case of STL, that cannot be done since a STL file holds all triangles as a single mesh object. But the other mesh formats I mentioned above can all store more than one mesh objects.

So in the case of the prospective customer I mentioned above, it would make sense to save individual objects or small groups of them in ArchiCAD to individual 3DS files and then import them one by one into Alibre Design using our add-on. I understand that the process may seem a bit tedious, especially for large models. But this method may actually end up yielding a desirable outcome as opposed to waiting endlessly for the add-on to stitch thousands of triangles and possibly run out of memory.

If you have any questions related to this issue, please do leave a comment. I will try my best to get you an answer or suggest a workaround.

  • jamesgardiner

    I could do this. Do you think there is a big demand for it? Don't mean to advertise but an example of a mesh in Alibre is here:
    http://www.femdesigner.com. The FEA module testing is still ongoing but the mesh shown there is just the usual collection of triangles in a vertex buffer to which I cunningly add contour plots via textures. The mesh is easily combined with the other solids on the same. In fact that is a pain for volumetric meshes :) because they occupy the same space, so I give an option to hide it.

    Off course I can show sliced tetrahedra too but that's a different issue :)

  • http://www.deelip.com Deelip Menezes

    People want to get meshes into Alibre Design so that they may do solid modeling on them (drill holes, shell, etc.) Is your mesh imported as a 3d solid or just a visualization graphics?

  • jamesgardiner

    Sorry I didn't make it clear I was just talking about this bit:
    “Neither does it have a mesh visualization structure like SolidWorks or Pro/ENGINEER”. Presumably 3DS mesh visualisation is a useful feature by itself. I'll put one together anyway at some point since the bones of it are there already.

  • http://www.deelip.com Deelip Menezes

    Yes, mesh visualization can be very helpful at times when you simply want to view the model and not do anything with it.

  • marcuswolschon

    “In fact, the time required increases exponentially with the number of faces to create, trim and stitch. “

    I would expect it to be linear (O(n)) in the nunber of faces,
    polynomal (like O(n^2)) at worst but never exponential (like O(2^n)).
    Your aproach seems to have quite an algorithmic issue there.

    I my own (unfinished) STL-code I´m at least combining coplanar, connected triangles into a single face.
    Special handling for the detection of at least round horizontal and vertical
    holes is planned for the time after it´s complete and working.

  • http://www.facebook.com/GloverRashad Rashad Glover

    I use stl 2 step. It is awsome. I also use sketchup pro and import my files to  Alibre 2011. I twas kind of hard at first but once you get the hang of it cool. Also if make sure your sketchup files are all separated before you bringing them in Alibre or your going to have problems.




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