# complex shape construction

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I am trying to create a 3d object that is essentialy like an undulating slab (sort of like a furling ribbon or arcing wing). I've got a contour (footprint) sketched on a one foot grid (x,y) and elevation info that tells me a numerical height (z) of the contour at each point where the contour/footprint intersects a grid line. Elevations on one side of the object's contour are often different from the elevation on the other side (ie- the surface rarely stays parallel to the working plane but instead furls up and down causing twists of various sorts).

I have tried making a 2d polygon of the contour in such a way that each vertex is located at a grid intersection, then converting that to a nurbs curve, then cycling through all vertices of that nurbs curve and typing in the correct z height . But when I try to make a solid object from the nurbs curve (so I can display it as a shell or thin slab) I can't get anywhere. I've tried coverting it to a nurbs surface and then using the shell tool but it will not compute. I can't figure how a mesh might work in this situation. Should I try to loft between two curves. There must be some way to do this but I'm not figuring it out. I have zyx cooridinates for each point where the contour meets the grid but I'm not sure how to use bezier curves because then the vertex of the polygon is the curve control handle not a point along the contour.

I read your description a couple of times, but failed to understand what you mean. It's probably my lack of understanding decent English. Could you post a couple of screenshots or other images to make it more clear?

Thanks,

BaRa

here is a link to some photos (rough models of the shapes i need to ceate in 3d cad)

Ischeer,

What are you going to do with the CAD model?

If you need all the detail, perhaps 3D scanning might be a better way to approach this shape. There are various application to convert scanned data to nurbs, if your application requires nurbs surfaces.

You might be able to model it in VectorWorks if you don't have other options, but other software may present a much faster and direct method.

I think a polygonal modeling program, with subdivision surfaces, might be a good option. If you need nurbs, you could then have the polygonal model converted.

Regards,

Chris

Don't try this in VectorWorks - the 3D navigation and manipulation tools don't allow you to model this within an acceptable timeframe. This is not a job for a CAD package like VectorWorks, but for a visualisation package or industrial design solution. Think Maya, C4D, Rhino, etc.

Good luck,

BaRa

I suspected that vectorworks might not be able to handle this but the reason I'm trying is cause I need to produce some cad drawings for structural engineering details (bracketing for a sculpture) and I use vectorworks as my primary cad program. All I want to do is get a very simple 3d representation of the basic form (just the outside edges as they describe an arching plane in space and not any of the specific inside forms). I've always put off incorperating other more sophistocated 3d modeling programs- besides, I'm MAC based and many of them are not available on this platform.

You could try one of the photo modeling applications. I know there's at least one (ImageModeler) available for the Mac. You would have to stick reference targets or dots to the object to define the curves, prior to taking the pictures.

You could get a general shape this way. I would not recommend this method if you needed more detail because it is very time consuming for a lot of points.

Chris

There are a couple of approaches you could take to this.

This looks like it may be handled pretty easily in a rough sort of way by creating loft surfaces with two rails (aka a birail sweep).

The other possibility is to turn your thinking 90 degrees and instead of trying to loft between two curves put in 15 (or so) curves along the legnth of the wing and loft those. Do it in a couple of sections and use the extend surface tool to extend one surface to meet the others.

BaRa may be right that there are other tools that may handle this sort of work a little more easily but the core functionality to make this shate does exist in VW.

good luck

Rick

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