This is my 1st post here.
In my day job I normally use the solid modeller, however I've been trying to learn more of the Shape Studio surfacing toolset.
My attached image shows a sequence of steps I took to create a sort of curved scoop in an existing surface, where I wanted to control the continuity of my surfaces closely.
I craeted the scoop by making a revolved surface and then creating a studio surface between the revolved surface and the existing surface.
I managed to control the surface continuity between the studio surface and the existing surface to either G1 or G2, and between the studio surface and the revolved surface to only G1.
The steps I took are as follows:
STEP 1 - created sketch on plane above existing surface.
STEP 2 - revolved sketch through 180 degrees, so the revolved surface overlaps the existing surface nicely.
STEP 3 - trimmed surfaces to leave the desired surfaces I wanted.
STEP 4 - created sketch on plane below the existing surface. I constrained the start points of the arcs in the sketch to be tangent to the revolved surface I created in STEP 2.
STEP 5 - projected the sketch onto the existing surface.
STEP 6 - trimmed the existing surface using the projected curves from STEP 5.
STEP 7 - Created a line between points on the revolved surface.
STEP 8 - extruded that line to create a sheet that would bisect the revolved surface.
STEP 9 - trimmed the revolved surface using the extruded sheet surface, and hid the sheet surface.
STEP 10 - Created a studio surface between the trimmed revolved surface and the existing surface.
I wanted continuity between the studio surface and existing surface to be G1 or G2, so that it faded out and no visible G0 line.
I have achieved G1 between the studio surface and the trimmed revolved surface, but this is not really what I was wanting, I really want G2, tangency and curvature continuous.
I am unable to get G2 continuity between the trimmed revolved surface and the studio surface when I try and use the arcs of the projected curve as cross curves.
I know I can't have G2 between these surfaces when using those arcs as cross curves, however I would like to know if there is a way I can achieve the same sort of overall look to my end result, with the fading edge at one end, but with G2 continuity between the trimmed revolved surface and the studio surface?
Instead of using a studio surface between the trimmed revolved surface and the existing surface, I attempted to use a section surface, fillet-bridge, and I managed to control the continuity to G2 and better control the shape using the skew and depth values at the start and the end. I still couldn't get close enough to my desired shape though, and even if I could, I wouldn't be able to trim the section surface to the existing surface to get the clean scoop I'm looking for.
Are there any advanced surface designers here who could suggest a way of getting the scoop shape I managed to achieve using the studio surface, but getting the G2 continuity between the trimmed revolved surface and the studio surface, so that the transition is much smoother than the G1 I currently have? I also need to maintain that G1 or G2 continuity at the other end to create that vanishing edge effect.
Hoping someone may give me a solution, possibly by making the surfaces totally differently from the way I have done them.
Solved! Go to Solution.
So one of the challenges of surface modeling is creating high quality continuity between regular mathematical surfaces (such as cylinders and spheres) and freefrom NURBS surfaces. I tend to work with one or the other and when possible (although technically not always doable) avoid mixing the two. So first I have a question for you regarding the requirements of the model. What are the technical constraint of the design, does the bowl have to be perfectly spherical? Do the edges have to be arcs and lines?
Can then better suggest a solution knowing the design constraints.
So you are wanting to create a surface that flows smoothly into the spherical depression. Do you want to control where it intersects the surface exactly with curves or can the intersection be defined by other criteria such as starting point or center line of the scoop surface?
With surfacing the key is to contruct curves to your techncial spcification first not to the end shape.
I think the issue is that rapid change in curvature at the corner point of the trimmed sphere.
You can get close if your guide curves are G2 to the trimmed edge of the sphere but to have it truly G2 you need to set back the two surfaces and create a bridging surface between.
One possibility attached.
Thanks a lot for taking the time to reply to my post.
I think the most important thing I want to achieve with the look here is:
1 - The trimmed sphere must truly be spherical
2 - The surface continuity between the trimmed sphere and the joining studio surface or whatever surface type it is must be G2.
3 - At the other end of this surface,it must be G1 or G2 to the existing surface to get the vanishing edge look I want.
I'll check out the model file you've attached is that using the bridging surface method?
Thinking about it again, I know you said that mixing the mathematically accurate sphere with the nurbs surface should be avoided, so if the bowl part can be constructed in another way using nurbs surface would that make life easier for achieving better surface continuity between the two nurbs surfaces?
Also, the arcs I've used in the sketch don't have to be so, if you can suggest a method here to get close to my original look, but which gives me the continuity I need them I would be v happy!!
The thing with using arcs that flow into the sphere edge, basically arc is that you have a mismatch of curvature at those points which make match the surface G2 more of a challege.
One method would be to first use the arc method you originally used then create G2 bridge curves along the arc and along the spherical edge. Do no have to run too far into each curve but enough to create a smooth transition of curvature.
In free form work I will often start with lines and curves to define the design contrains but then other nurbs curves (splines, bridge) and surfaces will be driven and contructed from them that are then used to contruct the final surfaces. This way you have dimesional control of free form geometry.
Thanks for the reply again, I understand the curve mismatch at the trimmed sphere and so I'll use the approach you advise of laying bridge curves on top of my arcs & constraining the first point of the bridge curve as G2 where it meets the trimmed sphere. That's a great tip so thanks.
What I really need is professional training on surfacing, I'm trying to get that arranged through Siemens just now. I'm a product designer by uni degree and I want to learn surfacing to assist me with my out of work consumer product designs. My day job is as a mechanical design engineer where I use solid modelling all of the time.
I'll let you know how I get on.