Full Version: creating nurb surface

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Hi airdog - right now MoI is mostly focused on drawing/construction type operations, like drawing curves and then creating surfaces by sweeping, lofting, etc... - it currently is not focused so much on squishing surfaces directly with control points.

That's because a lot of the types of projects that you might squish points around for tend to work better in a polygon / subd type modeler instead of a NURBS modeler. But I do expect to add more stuff for point manipulation in the future.

In the meantime, it is possible to set up a squishy surface like you want by using the Extrude command with the special "Set path" option.

To do this, start by drawing 2 curves at right angles to one another, using Draw curve / Control points. Place as many control points along each one as you want in the final surface, like this:



Then select one of those curves, run Construct / Extrude, and then push the "Set path" option that appears in the upper-right options area. Then you can pick the other curve, and a surface will be created.

This surface will be a combination of the control points of both those input curves, like this:



So you can now manipulate those points to squish the surface around:



In the future I expect to update Add pt so that it will work on surfaces, right now it only works on curves.

But the type of objects that MoI uses (NURBS) always have a regular rectangular grid layout to their control points, it isn't possible to add just one single point in the middle of a surface, you have to add a whole row or column of points. That's the reason why polygon/sub-d type modeling is usually better for a lot of point squish type modeling, you are more free to connect up points there however you want.

Hope this helps though,

- Michael

Attachments:
surface_control_points1.jpg
surface_control_points2.jpg
surface_control_points3.jpg

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cool!

just built meself a cube with this idea wich might come in handy!

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If I may, there's a secret for this process to work: you need to select the generated surface have "Show pts". (I guessed right, didn't I?)

Cheers,

- Diego -

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Hi Diego, yup that is correct - select the surface and use "Show pts" to turn on its edit points.

One quick note about "Show pts" - it does not work on all solids, it only works on a solid if all the surfaces touch one another at a "natural edge" rather than a "trimmed edge".

There is some description and illustration of that here:
http://moi3d.com/wiki/FAQ#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F

But you can always use "Show pts" on an individual un-joined surface though.

- Michael

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There seems to be a bad bug in using this technique in the latest Nov 12 beta.

When you go to pull points around after extrude->setpath, it adds edges to the surface which crease when points are pulled.

Edit
Did some further testing, it only happens when using polylines. Still works Ok when using curves.

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Hi kev, that's not a bug, it's normal for the surface created in this way to inherit the exact same nature of the curves that are input into it.

If you input a polyline, then the generated surface will behave like a polyline in that direction too, and when you pull around points of a polyline it makes sharp corners, so the surface created in that way will have sharp creases in it in the same way. When a surface is edited in such a way that it develops a sharp crease in it, it gets divided into separate pieces at the crease area, that's where those edges come from.

If you want it to deform smoothly, you'll need to give it input curves that would deform smoothly themselves, that's why the original instructions mentions using Draw curve / Control points specifically.

- Michael

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