Ah, 2 good ideas - thanks Burr!

Hi NightCabbage,

> Ok, so that makes sense, but still, shouldn't I then be able to
> adjust the trimming edges?

Well, no - not to reshape the surface.

The trimming edges are things that are contained within the surface, marking which parts of the surface are active or inactive.

The trimming curves themselves do not define the shape of the surface geometry - the surface's control points are what do that.

This may give you a better idea of what I was describing earlier, about why you can't just pull any edge curve around to reshape a surface with NURBS - if it is a trim curve it is not defining the shape but instead marking active/inactive regions on the surface.

- Michael

Hi NightCabbage,

> Also, perhaps I should be using something like Network
> instead of Planar for this kind of thing?

No, for planar surfaces it is normally best to use Planar and get a simple plane that is trimmed like you did already.

Network has the requirement that you have to give it a regular criss-crossing grid of curves, you can't just grab any set of random curves and use Network on them, they have to have a grid pattern which can be bending or compressed in different areas, but still needs to have the same kind of grid thing as longitude and latitude lines on a map. Basically there has to be a rectangular pattern to the curves to be networked.

- Michael

Thank you for the explanations Michael :)

I think I understand it, but I'm still not sure why you couldn't change the trimming curves, except for the one problem of if you tried to move then outside the surface.

Hi NightCabbage,

> I think I understand it, but I'm still not sure why you
> couldn't change the trimming curves, except for the one
> problem of if you tried to move then outside the surface.

Well, you can't re-shape the surface by changing the trimming curves, which would probably be normally what you would expect to do by editing them like you would in a polygon modeling program.

For example, when you edit edges in a polygon program, it is not unusual to move the edge up or down in 3D or stuff like that to mush the points all around.

It would be theoretically possible to edit the trimming curves but it would not behave like the polygon modeling editing, it would be more like you would drag the curves around within the surface but not be able to move them up or down off the surface or stuff like that.

In the future at some point it would be good to try and enable that kind of special trim curve editing, but it will take quite a bit of work since there are all kinds of situations to look out for, like you can't make trim curves cross over one another or have outer loops cross over inner loops, deal with other edges and loops that are joined with that one, etc... etc...

- Michael

I think I'm beginning to understand the complexities of a NURBS system...

I'm glad to see that you're interested in adding these features in, however, as I really think you have a great product :)

Hi NightCabbage, yup I'm definitely interested in them, but they aren't really a "natural fit" with the NURBS structure and will require quite a lot of work to make them happen in a way that does not make broken or invalid objects too easily.

So that means I don't really know when it will happen, possibly not for a fair amount of time.

- Michael

I usually use the command 'ShrinkTrimmedSurface' which shrinks the underlying surface to the boundaries of the new shape.
You can find the explanation here....... http://moi3d.com/wiki/Hidden_Secrets
12th Secret from the top.

Cheers

I also struggled a bit with NURBS at the start. I had only just started to get the hang of polygons :-)

I try to think of NURBS more as a block that I am going to cut bits away from to make my final shape. I use other shapes to cut the block into whatever you want. I use booleans and extrudes more than planes.

For your building I would have started with a block then used another block to cut out the corner. This would have left me with a solid model.