Highlight puddle caused by star point

[ant77]

Hi, I'm having trouble with a highlight puddle caused by a star point:

The TSplines manual recommends that star points should be placed on "flatter parts of the surface to more predictably obtain an aesthetically pleasing model'. This surface is not flat, but certainly isn't radically curving, and is distant from an edge. Point editing doesn't fix it, nor does 'make uniform'.

Unfortunately to get the model finished we had to patch it in Solidworks:

Patched.jpg (29.62 KiB) Viewed 789 times

None of us felt very good after that...

[Matt Sederberg]

Here's a post Sky wrote about how he approaches this issue...

http://betterlivingthroughcnc.com/2011/ ... ar-points/

[ant77]

Thanks Matt, here's what it looks like after applying Sky's technique. Not perfect, but maybe a little more point editing before subdividing will improve things...

Resulting surface after applying Sky's technique

star-point-wobble-2.jpg (76.17 KiB) Viewed 764 times

[stratosfear]

Hi, Ant

The topology for this model looks like a complete mess to me. Please post a file so that we may help you. You have far too many star points and I can't figure out why you have a creased edge where a planar surface should be.

[ant77]

Hi, here's the file. I only have Rhino v4 so if you post a change could you please use that format? Thanks for offering to take a look.

[stratosfear]

Hi, Ant

Not all the edges along your model's hard edge were creased. However that's not really important because all those faces are unnecessary as they are better handled by a planar surface. After I deleted them and ran the remove crease and make uniform commands, your model started to look good. I used Rhino's rotate command to better align the model to the origin. I then moved some some of the verts around the star point with the translate manipulator set to the UVN Dragmode. I also used the SetPt command to better align some the verts along the outer edges. After that I converted it to a polysurface.

I decided to show you an alternative approach to this model using Rhino's patch command. I used Rhino's duplicate edge command over the polysurface to extract all the curves. I should have rebuilt all these curves and then done some point editing but I felt the results were good enough. This surface is degree 3 and can be point edited in it's un-joined state. Solidworks is incapable of producing a surface like this as it's spline functionality is seriously sub-par.

I hope this is helpfully.

[ant77]

That's awesome, thanks stratosfear!

I was able to replicate your results on the original model. The step that had the biggest impact was to remove the crease and then run 'make uniform'. That fixed the puddle, and then I could reapply the crease without the puddle returning.

You didn't mention above that you have deftly removed two of the star points on the planar face, nice work! I take your point though that it's better to make planar faces as regular nurbs faces, and only use t-splines for the organic shapes. Juan said something similar in another post.

Thanks for the demo of Rhino's patch command, it looks really powerful. As a purist however I like the fact that the isoparms of the converted t-spline surface are all running in the right directions.

Thanks for taking time out to help me.