water-tight model of a face scan in 3d

[Mihaly]

Hi, I have a laser human face scan which consists of topographical-line-like curves about every .05 inch. I need to make a water-tight model. I suppose I could model it in either mesh or nurbs and still export a stl file, right?

What's the easiest was to do this with Rhino? Or, what are the best several different ways to do this? Should I use the loft command then somehow find the edges and then make a planar back to the face mask?

In my true ideal world I'd make the mask like a shell .25 or .5 in thick. But really, I'd just be happy with whatever is the quickest was to make it a water-tight model. Should I just make a zillion polysurfaces then weld each of them together until the object has no holes? This seems like it could take a week.

I have Rhino 4, but presumably there's no free downloadable software that could also help simplify this process(?)

[awerby]

First make a surface by trimming all those curves with a plane so each is separate, then using the Interpcrv command and the Near object snap to create a grid where each new curve crosses each original one. Use the NetworkSrf command to create a single NURBS surface. Then offset that surface inside, so that you have an outer surface and an inner one. Split them with a plane to remove ragged edges, and split the plane with the surfaces to make a flat surface that connects the two face surfaces. Join all 3 surfaces to create a solid (as far as Rhino's concerned, anyway) and if you want to print it on an additive RP machine, save it as a STL file without open objects.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[Mihaly]

Thanks Andrew,
You're the Man! I trimmed off a little part of the chin to make a small sample model before I go over the whole face. I did all the steps you described. It seemed to work perfectly. I don't see how it couldn't have been watertight. Then I clicked "save as". But Rhino said "The STL File you are saving is not adequate for creating rapid prototyped parts."

So I went back into Rhino and converted the nurbs model to a mesh. Then I tried mesh repair tools, but when I tried to save it as an stl I got the same warning. What can I do? When Rhino says it's not adequate, does that mean it's probably really not watertight.

[awerby]

If you just made a surface, then it won't work as a RP file, since it has no depth. You need to enclose some volume before it will work. If you did make a Rhino solid and it still didn't work you might look at your tolerances - they might not be tight enough to close all the seams adequately.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

Thanks Andrew,
You're the Man! I trimmed off a little part of the chin to make a small sample model before I go over the whole face. I did all the steps you described. It seemed to work perfectly. I don't see how it couldn't have been watertight. Then I clicked "save as". But Rhino said "The STL File you are saving is not adequate for creating rapid prototyped parts."

So I went back into Rhino and converted the nurbs model to a mesh. Then I tried mesh repair tools, but when I tried to save it as an stl I got the same warning. What can I do? When Rhino says it's not adequate, does that mean it's probably really not watertight.