Let me start out by saying I am not a MOI user, but we are looking into MOI and I am wondering if I could get some feedback or suggestions as to whether or not MOI would be an appropriate tool for what we would like to do.

Basically we have a design that we would like to import into Alibre. However, it is currently created/generated as a large mesh and we would like to remodel it as a nice smooth continuous surface that we can easily and quickly import into Alibre. I wrote a little blog entry which shows pictures and slices of the shape we are modeling. I can already generate the shape as a 3d mesh, but this is really non-optimal to try to import into Alibre.

http://www.flightgear.org/blogs/curt/uas/misc/3d-modelling-with-perl/

I can separate the top and bottom halves the the model and each half is then really well behaved. I forget the word I want, but for every X,Y horizontal location, there is only one Z value. From a top view perspective, the shape never overlaps itself and is one continuous surface within the overall outline.

I can generate my mesh (i.e points on the surface of the mesh) with pretty much any resolution ... just a few points as a reference, or tons of faces. I can import my mesh into blender and export it in a variety of other 3d formats (but all still as a mesh.)

We would like to import our shape into Alibre so we can add some additional things to it, draw the interior components, etc.

I am wondering if MOI would allow me to do this?

I don't necessarily need to do a surface fit of an arbitrary mesh (if I can do a direct fit, that's great, and as I pointed out my surface is well behaved in terms of not overlapping itself when viewed from the top down.)

The final surface we generate doesn't *have* to be an *exact* fit of the original mesh. The mesh that I have generated is an approximation of the original prototype which was hand made, so we have some flexibility with respect to the final exact shape as long as it captures the artist's intent.

If I provide a set of points *on* the surface of my shape, can MOI fit a surface through those points? If I provide a top down "outline" of my shape, can MOI clip the surface within that outline?

I spent 2 days writing the perl script to generate a mesh surface of our design, so it seems like it can't be *that* hard to model this same shape in an advance modeling tool. But we are struggling to find a way to bridge from where we are now: "a big mesh of triangles" to where we want to be: "a nicely modeled surface in Alibre."

Any suggestions? Is MOI the silver bullet we are looking for? Are there better ways to create a curved surface for Alibre when there is a requirement that it matches an existing curved surface and outline pretty closely?

Thanks in advance!

Curt.

Did you know that MoI has a Conic tool with an RHO input???

Do you have a sample file you can post here?

Hi BurrMan,

Thanks for the reply. All I know so far about MoI is what I'm learning from the web page and forum here. I don't know all the MoI and 3d modeling lingo so I apologize that I need a little help just understanding your message.

Conic tool would imply a tool to make cone-like things, right?

I don't know what "RHO" stands for?

I'm guessing you are talking about some tool that can create a shape by rotating some curve around an axis (kind of like what a lathe could physically do?)

Our design doesn't really have any rotational shapes in it though.

The link I included in my original message shows the shape and a breakdown of the cross sections pretty clearly, along with a couple 3d renderings (wire frame and solid/shaded.) If there is a reason to post a 3d mesh file, I could probably generate a low res version for quick download ... what format works best?

Thanks.

Hi Curt - No I don't think that MoI is the right tool for the particular job that you're describing there.

You're talking about what is called a "Reverse engineering" workflow - that's where you are trying to construct a model to fit it to some kind of existing data (either a point cloud, polygon mesh data, etc...).

That's a much different area of work than what MoI is focused on - MoI is focused on drawing shapes from scratch where you are creating the model directly. It is not focused on reverse engineering a model from some existing surface point data as you need.

There are some reverse engineering tools out there that are specifically focused on the kind of thing that you need to do though - one of the main ones is called Geomagic: http://www.geomagic.com/en/

There are also a few different kinds of reverse engineering plug-ins that you can get for Rhino, it's possible that one of them could do this kind of a job:
http://www.rhino3d.com/resources/default.asp?category=13&language=en

Also if you can get a set of points as you describe into Rhino you could try using Rhino's "Patch" command to try and fit a surface through them, that may work if your surface is pretty simple and does not really bend around very much.

But no, MoI is not really the right tool for what you are describing.

- Michael

Hello Curt

I've been trying to find something affordable to convert a poly mesh to nurbs and finally came across http://www.resurf3d.com/

They have a RhinoResurf plugin (for Rhino of course) to do this, and 2 stand-alone applications:

Mesh2SingleNurbs - I have tested and purchase this and have produced some reasonably good nurbs approximations. I can tell you is that the surfaces are not perfect, but they might be usable for you. I have not tried editing them in other applications.

PointCloud2Nurbs - I have tested this and was unable to get any of my files to produce anything usable. The demo file supplied with the app did work, but it had too few points to be useful for me. Might work for you though. I was using pointclouds with 0.5 - 1.0 million points.

You can download fully functional demos (time limited) to see if they will work for your purpose.

Good Luck,
Chris

Hi Michael, thanks for the comments.

I just downloaded the demo version of MoI which I probably should have done before my original post.

One advantage we have on this project is that we don't need to exactly reverse engineer the original design. We just need to capture it's essence. My mesh model I created is not exactly like the original prototype, and the prototype isn't exactly like the artist's 3 view (not to mention the artist's top, side and front dimensions don't exactly all match up either.) So there is some flexibility in the final result.

This is an RC scale aircraft (7-8 foot wing span) so the only major constraint is that we need the *exact* airfoil contour where the wings plug in. I have this contour as a series of X, Y data points. Is there a way to import a set of X, Y points into MoI and build a curve that passes through those points smoothly and exactly? There's about 60 data pairs, so it would be pretty tedious to plunk these in manually.

In my own little program that generated the mesh model of our design I just loaded in the X, Y points and built a cubic spline out of them. Can I create a curve in MoI from some external set of coordinates?

After playing with MoI for 10 minutes, I think that if I could import the exact airfoil contour somehow ... then I could mess around with the other curves and build the rest of the shape by dragging the control points around interactively. Once I had the airfoil locked in, I could probably spend 10 minutes on all the other parts and be awfully close to final result.

Is it possible to import a set of curve coordinates from some external data file?

Thanks,

Curt.

Hi Curt,

> Is it possible to import a set of curve coordinates
> from some external data file?

There is a plug-in that you can download and copy to MoI's commands folder which will then make a new command called ImportPointFile available which can do that, see here:

http://kyticka.webzdarma.cz/3d/moi/#ImportPointFile

- Michael

Hi Curt,
A conic curve is based off of a parabala type curve, so yes a cone is involved, though a conic curve is a type of analytical curve..

Conic curves and RHO values were used to design "airfoils"..... FOr a wing, you could have your "exacting measurements".

And as Michael said, I wouldnt want to try to reverse it, though from what I saw in your link, you should be just creating this stuff in MoI, from the start!

Hey guys thanks for all the help. Using the ImportPointFile extension, I was able to import the slice boundaries I generated externally from my script as curves in MoI. Then I was able to generate a quite nice "Network" surface from them. Now I get to send it up stream so hopefully it doesn't come back for more tweaks. :-) Wow, MoI is a very cool and intuitive program ... really impressed with it.

Ah yes, another bitten by the MoI bug...welcome Curt :)

Cheers

""""""""""Ah yes, another bitten by the #########MoI bug###############...welcome Curt :)"""""""""""""""""""

Sacrileges!!!!!!!!!!!!!!!!!!!!

lol.........not that type of bug Burr!

Cheers

Hi Curt,

Can you make a scren shot and share it with us on what you have done with MoI and import points ?

Thanks

Here's a quick screen shot. I have to apologize ... I'm normally a Linux user and I can't remember the magic combination of keystrokes to grab a screenshot on windows. Could probably google it in 10 seconds, but it only took 5 seconds to whip out my cell phone ... :-)

Key of the keyboard "Print Screen" ;)

In MoI, there is also a script to capture the viewport at "Any Resolution".... So if you want a high quality image, like 4000x4000, you can set that and get an image of your model!!!!!!!!!!

Very cool....