Plane Problem

 From: NightCabbage 27 Aug 2009  (1 of 14)
 Hi guys Ok, so I've create this object out of lines, and then used Planar to put a surfaces where I want them... But as you can see, when I use show points, it gives me these as the points, not the actual points of the lines that the shape is made out of... Here is the file... building.3dm Thanks!

 From: Michael Gibson 27 Aug 2009  (2 of 14)
 2884.2 In reply to 2884.1 Hi NightCabbage, yup that is normal - what you see there is the "underlying surface" which is a plane that is made up of 4 control points. All NURBS surfaces have an underlying surface, which has a rectangular type grid of points. (not necessarily just 4 points, on other surfaces especially curved ones, the point grid can have more points in it than that, the 4 point one is the most basic one). Then there can be trim curves on that surface to cut different areas away or make holes. When you use Construct / Planar, it builds a large plane going through those curves, and then those curves become trim curves on that plane. There are some other illustrations showing that exact same kind of thing in that FAQ answer That whole mechanism of "underlying surfaces" and "trim curves" are one of the big differences with NURBS models as opposed to polygon models. - Michael EDITED: 28 Aug 2009 by MICHAEL GIBSON

 From: BurrMan 27 Aug 2009  (3 of 14)
 2884.3 In reply to 2884.1 NightCabbage, THat is the "Underlying Surface" that Michael had spoke to you about in a few threads back regard how nurbs work. Try selecting all the edges of that surface and deleting them and see what happens. THis is the "Trimmed Planar surface" that you created [EDIT] Foiled again by that MoaI Guy! [EDIT]

 From: NightCabbage 27 Aug 2009  (4 of 14)
 OOOHHHH! That's what you mean by "trimming"!! It literally trims a part of the surface to the shape that you want! Hah! That makes sense now. Ok, so that makes sense, but still, shouldn't I then be able to adjust the trimming edges? Also, perhaps I should be using something like Network instead of Planar for this kind of thing?

 From: BurrMan 27 Aug 2009  (5 of 14)
 2884.5 In reply to 2884.4 You can select all the edges of that surface and copy and paste them, then delete the surface. Now select all the edges and join them, then show points and adjust them. Point pulling on solids and surfaces is not a prefered method of working with NURBS. [EDIT] Deleted some as it was incorrect info[EDIT] EDITED: 27 Aug 2009 by BURRMAN

 From: NightCabbage 27 Aug 2009  (6 of 14)
 Ah, 2 good ideas - thanks Burr!

 From: Michael Gibson 27 Aug 2009  (7 of 14)
 2884.7 In reply to 2884.4 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

 From: Michael Gibson 27 Aug 2009  (8 of 14)
 2884.8 In reply to 2884.4 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

 From: NightCabbage 27 Aug 2009  (9 of 14)
 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.

 From: Michael Gibson 27 Aug 2009  (10 of 14)
 2884.10 In reply to 2884.9 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

 From: NightCabbage 27 Aug 2009  (11 of 14)
 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 :)