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Loft Problem


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I am trying to loft two nurbs and they are not taking. I am posting a file and a link to a video of what I am seeing. I am hoping this is a operational problem of something I am unaware of and not just a bug.

Any help is as always appreciated.

Matt

Edited by MattG
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Matt

The inner nurbs curve has a sharp hitch on the bottom left corner and a discontinuity on the bottom right corner. And one curve has clockwise direction and the other has a counter clockwise direction. And one curve has 27 vertices and the other has 25.

One or some combination of those caused the failure.

I've found that when using the first mode of the loft tool (and the 3rd mode, for that matter) for objects like this it helps to have the same number of vertices in each curve. That way the loft tool doesn't have to pick what face to make a triangle.

By using the polyline tool I was able draw each shape w/ 15 vertices and it worked fine.

hth

mk

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Matt,

There are some small geometry issues that are causing things to fail. Both shapes have points that are almost co-incident but not quite so they are not actually closed shapes.

Snap one point to the other. Decompose and then recompose all the resulting NURBS curves to create a closed shape.

Also, each profile has a different number of points. That won't make things fail but does create a messy shape. Deleting them aligns things for a cleaner loft.

And as Michael mentions, they are running in opposite directions.

Kevin

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Edited by Kevin McAllister
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Thanks guys, sorry I didn't really thing of that. I created the geometry offset from each other performing the same operations so it is a little surprising that they ended up being slightly different.

I actually pulled this out of a file and there are about 8 layers to this. This was the only one I couldn't get to work, but that does make sense.

I did know about the closed and not closed portion of this. However I didn't realize they wanted similar number of points.

Thanks,

Matt

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I suspect it was the combination of all the issues more than anything.

They don't necessarily need to be closed shapes. Almost closed is more likely the culprit. Really open or entirely closed is probably best practice.

I did a test and they don't even need to be running in the same direction, its just really messy if they're not.

KM

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What determines direction? The way I made those shapes was to start with a rectangle and set it to the dimensions I wanted. I drew a arc along one side. I mirrored the arc. I trimmed the piece in the arc to create 2 lines and 2 arcs. I composed them.

I than went about drawing the little insert piece, mirrored it, and subtracted the two pieces from the larger piece. Like I mentioned I did this about 8 times and only one came up with this issue. I guess I am curious what determines direction in this scenario and how I could avoid having this issue in the future.

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Can't prove this is true, but....

For polylines and polygons that are converted to nurbs, the direction is taken from the direction drawn.

For other shapes like rectangles and arcs, it just decides. Maybe it's clockwise in the northern hemisphere and counter clockwise in the southern.

In practice it doesn't matter until you're ready to make a loft object. Just check Show Direction in the OIP before running the loft tool or, when running the loft tool you have a chance to check and change the direction of all the nurbs curves in the dialog box after the green checkmark.

Either way, you can usually create the loft object with curves running in opposite directions, it just gives you a not very useful shape.

hth

mk

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Matt,

Just making sure you know about Adding and Subtracting surfaces and the Paint Bucket mode of the Polygon Tool.

I tend to draw using surfaces with lines as guides only. In your case I would draw the rectangle and filled arcs. Send the rectangle to the front and subtract surface from the arcs. Delete the unneeded arc remnants (the points) and then select all three elements (rectangle, two arc shaped polylines), combining them with add surface.

Also note if you hold down shift while using the Polygon Paint Bucket you can keep adding to the initial shape it creates. The OIP tells you if a polygon/polyline is open or closed. Make sure its closed before converting to NURBS. The 2d polygon/polyline editing is much easier than editing the NURBS after.

Kevin

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