Points on All Primitives

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 From:  Brian (BWTR)
3227.1 
An update to 3D Coat today really highlights the potentials that could be advantageous in MOI.

Is there any big problem in having all the primitives to come with the points as we can get with the sphere?
(Sorry if this duplicaates earlier posts)

Brian
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 From:  Michael Gibson
3227.2 In reply to 3227.1 
Hi Brian, the way MoI's NURBS geometry works is very different from 3D Coat.

It is difficult for MoI to have control points turn on for primitives that are made up of trimmed surfaces, rather than all untrimmed surfaces.

You can actually turn them on if you want by using Edit/Separate to break an object into individual surfaces - you can always turn on points for just a single surface that is all by itself.

But by default MoI does not turn them on for joined trimmed surfaces since it would be too easy to pull things apart and end up with gaps between what used to be a shared edge.

For some more information and illustrations, please see this FAQ entry:

FAQ: Why does show points work for some objects but not others

It's easier to have points on all the time for a polygon-based modeling system than a NURBS-based one, due to the system of an "underlying surface with trim curves", that is used with NURBS. But it is also that same system that makes booleans work much better with NURBS as well.

If you want to work with surface points a lot, you may want to use a polygon modeling system for that particular kind of work rather than MoI.

- Michael
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 From:  Brian (BWTR)
3227.3 In reply to 3227.2 
Thanks Michael, I had not picked up on that one.

In effect, if fractionally different working proceedures, it really does get much the same similar end result to the new "special" primitives options in 3D Coat.

Brian
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 From:  Michael Gibson
3227.4 In reply to 3227.3 
Hi Brian, yeah actually another thing you can do instead of Edit/Separate is to select the caps and delete them, leaving only the cylinder or cone surface which can then have points turned on.

Then after you have squished the points around if the end is still planar you can use Construct > Planar to recap it, it looks like you have probably already figured that out.

It's those end caps on a cylinder or cone that are trimmed surfaces, they are a larger plane that has been trimmed down to a circular outline.

- Michael
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 From:  jbshorty
3227.5 
Hi Brian.

You can easily make your own single surface primitives:

Cone = Revolve
Tube = Revolve
Cylinder = Revolve
Box = Rail Revolve

Just be sure that your input curves don't have any sharp points, and they will remain single surface and point-editable. The control point structure of the input curves will determine the point structure of the resulting surface...

jonah
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 From:  Michael Gibson
3227.6 In reply to 3227.5 
Hi jonah, actually it is not necessary to do anything special to set up a control point editable box in MoI unlike Rhino.

That's because MoI has a feature where it also allows you to turn on control points for a polysurface if the polysurface is made up of untrimmed surfaces that are joined to one another along a natural surface edge.

So in MoI you also don't need to worry about not having sharp edges in your revolve profile, the part that you do have to worry about is planar end caps since those are trimmed planes.

- Michael
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 From:  jbshorty
3227.7 In reply to 3227.6 
Hi Michael. I was assuming that Brian wants to manipulate these in some way, perhaps make them "squishable" as with the sphere primitive...
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 From:  Michael Gibson
3227.8 In reply to 3227.7 
Hi jonah,

> I was assuming that Brian wants to manipulate these in
> some way, perhaps make them "squishable" as with the
> sphere primitive...

I guess you mean making more internal points for the box? Yeah if you want to have more points to squish around instead of only points at the box corners then you may still want to use rail revolve for that.

But you do not need to worry about the sharp corners in the revolve profile preventing control points from being turned on like you do in Rhino, since MoI allows points to be turned on for objects made up of more than one joined surface if the joins are at natural surface edges.

Of course if you want to have a totally smooth shape throughout then you should not have any sharp corners in the revolve profile since you will be starting out with sharp corners in that case.

- Michael
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 From:  Brian (BWTR)
3227.9 In reply to 3227.8 
Michael/Jonah

Jonah's idea adds a lot to modelling approaches. Whacco!
Between the two of you it really reduces the need to work with poly apps .

Thanks
Brian

EDITED: 6 Jan 2010 by BWTR

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 From:  jbshorty
3227.10 In reply to 3227.8 
Hi Michael. A similar thing can be done in Rhino by using the SurfaceCreasing plugin, which allows you to output a creased single surface from commands such as Extrude, Sweep, Loft, etc. Any kinks in the curve will become a crease. Of course, it has the same toplological restraints as a single surface. But it can be point edited... It can be a very useful tool, but dangerous in the wrong hands! Many times resulting in the question "why can't i fillet this edge?". And the usual response "because there is no edge there!" :P

jonah
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 From:  Brian (BWTR)
3227.11 In reply to 3227.10 
Good fun!
Brian
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 From:  Michael Gibson
3227.12 In reply to 3227.10 
Hi jonah,

> It can be a very useful tool, but dangerous in the wrong
> hands! Many times resulting in the question "why can't i
> fillet this edge?". And the usual response "because there
> is no edge there!"

You'll probably also run into other problems in Rhino with surfaces like that, like meshing not working correctly in all cases on such a kinked single surface and also potentially problems in surface intersection and booleans as well. Also you can't use Explode on that kind of thing to break it into components anymore like you normally would be able to do with a faceted object.

The nice thing about MoI's method is that it just works directly on a polysurface, there is no need to set a special mode to create unusual geometry and so you don't need to run into all those side effects.

- Michael
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 From:  jbshorty
3227.13 In reply to 3227.12 
Hehe... Yes the meshing is the other question which people always ask. The mesh generates just fine. But the vertices on the crease are not welded as they would be for an edge. So once you move the points, the vertex shading normal sometimes gets a bit screwy... Rhino does have a command to split it into a polysurface, called DivideAlongCreases. So you can continue adding fillets, etc...
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 From:  Michael Gibson
3227.14 In reply to 3227.13 
Hi jonah,

> Rhino does have a command to split it into a polysurface,
> called DivideAlongCreases. So you can continue adding
> fillets, etc...

Yeah, but this is another good example of how Rhino has gotten so far out of hand with such an enormous pile of commands...

MoI just always splits kinked surfaces into a polysurface, but without losing the ability to point edit it.

Basically the need for the extra command has been engineered out of MoI by an improvement in a more fundamental mechanism (just regular turning points on).

- Michael
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