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Snap to vertex?


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What would be incredibly useful to me- maybe there is a way to do this, but I haven't seen it- is the ability to snap a given NURBS vertex precisely to a vertex on another NURBS object.

I'm creating very complex curves and would like to use the create surface from curves tool for some objects, but find that I can't reliably edit the vertexes to create intersections. Snap to objects works if things are drawn exactly right, but the intersection is lost if you do any keyboard editing of the vertex positions- even keying them into the same X/Y/Z positions does not create an intersection.

Does anyone have a suggestion for ensuring that given curves intersect at a particular location in space?


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I'm using 10.5. I may not totally understand the snap features in the new release, though. Will they work to snap a vertex to another object when you are only moving a single vertex, not the whole object?

I'm fairing complex curved shapes by adjusting the NURBS vertex of the defining curves through keyboard entry, and I'd like to be able to make sure the two curves intersect when I move the two vertices to the same location.



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  • Vectorworks, Inc Employee

In VW10.5, I think you can snap to points on another object while reshaping. As you might have noticed, you can snap to the control points of the NURBS curves (hint comes up as "Point"). You can also snap to any point of a NURBS curve. Double click on the Snap to Object button in the grid palette. You will get a dialog - turn on the snap to Edge Point - and you should be snapping to all points.

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Thanks for the suggestions- I've tried to use the snap to edge constraint, and it does work to create intersections when drawing or dragging vertices, but does not appear to work when entering values from the keyboard.

What I would like to be able to do is to draw a NURBS curve constrained in one dimension that will snap to intersect with my other NURBS curves - like a topographical contour line, or the waterlines on a boat hull intersecting with cross sections through the hull.

I may be missing an obvious way to do this, as my experience is limited, but if I have

1) the constrain to working plane constraint turned on, and

2) the snap to edge points checked, and try to draw a NURBS curve, the snap to edge points does not work to place the vertex at the intersection of the working plane and the curve I'm trying to intersect with.

If I don't have constrain to working planes switched on, the vertex is not placed at the working plane either. Is there a simple way to draw something like a contour line that would intersect other curves and constrain it in one dimension?

My workaround has been to create a NURBS surface, position it sectioning through the curves, use the NURBS analysis tool to place a 3D locus at the intersections, then draw a NURBS curve through the loci. However when I do this many of the curves don't actually intersect, although they appear to do so in the drawing. I'm going to try this again, though, I'm not too sure that I have had the snap to edge constraint turned on when I was doing this.


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Well, now this is getting frustrating- I am still having difficulty getting NURBS curves to make a surface. Here's what I'm doing:

I have snap to edge points turned on from the constraints palette. When I draw the curve, the "POINT" cue comes on, and the curve I'm drawing appears to snap to the other curve at a vertex. However when I try to create a surface a good portion of the time there will be an error: "surface could not be created from curve network". Usually when I look up good and close, the curves are not intersecting- though the cues were there and made a nice "snap" sound.

When reshaping a vertex, likewise, the points appear to snap together. They show as being in the same position in the object info palette. The points appear exactly coincident, even when I zoom in 50,000% or more.

If I use the NURBS analysis tool to check the intersection, only one 3D locus is placed at the intersection, not 2 as would be if they did not intersect.

But when I select "create surface from curves" from the model menu, I get the message "surface could not be created from curve network".

By only adding one curve at a time, getting a failure, then systematically eliminating intersections with other curves until the surface creation succeeds I can slowly isolate the problem intersections- but snapping the vertexes again does not always succeed. Sometimes it does, and I can add another piece to the surface. But if it doesn't snap right away it does not seem to matter how many times I reposition the vertex with either the "POINT" or "OBJECT" cue showing- the create surface command will fail if that intersection is included. I don't see any difference between the successful and the failed intersections. With a minimum of 170 intersections it's pretty tedious- one failed intersection means redrawing a line with many intersections, any one of which could fail as well.

I'm assuming curves not intersecting is why the Create Surface from Curves fails, but maybe I'm missing something basic here?

VW- it would be a lot easier to troubleshoot this stuff if the curves missing an intersection were indicated.

RonR [Confused]

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