trouble with section cuts and planar surfaces

Dear all,

I found myself in some trouble with grasshopper, hope someone came across the same and knows how to solve it.

I've created a model in consisting of three lines, divided in equal parts and then connected via curves. Eventually loft the curves to get a closed Brep. (see attached pictures)

Now I want to make section cuts (along an orthogonal axes) but since these sections sometimes cut the earlier created curves the created sections are 3 Dimensional instead of planar.

this leaves me with empty sections, which is causing me trouble.

Does any one no how to solve this? is there an possibility to make a smooth surface from the loft, where it doesn't have the history of the original lines in it?

Thanks,

Tijl

Attachments:

Replies to This Discussion

Permalink Reply by Tijl Uijtenhaak on February 6, 2011 at 2:12pm

extra file of zoomed in trouble, the two lines crossing and both becoming the section (non planar).

Attachments:

trouble.jpg, 141 KB

Permalink Reply by Tijl Uijtenhaak on February 9, 2011 at 9:35am

All,

After emailing my trouble to Giulio of McNeel he found out that the section outcome was wrong since i used a straight loft.

If this loft(see ghx file, attached) is set to normal, this solves the problems.

Unfortunately if the value of divisions in this example is less than 67 the joined loft becomes an open instead of closed Brep.

Although for now the outcome of my problem seems all right, it does feel strange that this change happens.

It also happens if I scale the lines by any factor larger than 1.

This time I do add the files instead of the pictures, so if any one fancies a look to help me solve this mystery, please!

Tijl

Attachments:

20110209_loftTrouble.ghx, 900 KB
20110207_HalSections.3dm, 56 KB

Permalink Reply by Tijl Uijtenhaak on February 9, 2011 at 10:03am

Found the problem with open Breps.

This causes non closed section lines and therefore it is not possible to make planar surfaces out of the sections, something i need further down the process.

Permalink Reply by Giulio Piacentino on February 10, 2011 at 2:14am

You could use the original curves to close the brep, like in the attached definition?

- Giulio
____________
giulio@mcneel.com
McNeel Europe, Barcelona

Attachments:

20110209_loftTrouble-originalCurves.ghx, 904 KB

Permalink Reply by Tijl Uijtenhaak on February 10, 2011 at 3:36am

For the top part of the GH file it would be perfect if I could realy make a volume out of the three lines, but i don't know how to do this so it follows the interpolated curves and create a closed Brep. Therefore i divided the curves in as many divisions as possible (or as many as my computer can render). If I then use the drawn curve it will never perfectly close the total volume.

For the bottom part i do want to approximate the curves by poly lines this to compare the volume difference if you use less divisions. I might do this the hard way, creating sections, extrude these and then solid difference the two selections (basicaly integrating in a finite set of steps)

If i scale your solution i get back into the open Brep and therefore no closed planar surfaces that i can extrude later in the process for my 'intergral' solution.

Hope this answers your question, Thanks for digging into this!

Tijl

Permalink Reply by Giulio Piacentino on February 11, 2011 at 1:18am

Hi Tijl,

I've added a couple of more normal lofts and used interpolated curves among the divided points. Please see if this helps any further.

- Giulio
___________

giulio@mcneel.com
McNeel Europe, Barcelona

Attachments:

20110209_loftTrouble-moreNormalLofts.ghx, 932 KB

Permalink Reply by Tijl Uijtenhaak on February 11, 2011 at 7:56am

Hi Giulio,

This does help, but again changing the number to say 3 it creates an open Brep again..

I came up with an other idea, being to extrude the edges of the loft.

This goes well if the curves(vertical) aren't divided up in segments. (see top of grasshopper canvas)

If the vertical curves are divided than the edges suddenly become many and its hard to understand how to solve the edges. But getting these from the polylines the first loft was created by creates an closed Brep again: see middle bottom and middle top grasshopper canvas

So I think this is solved but i did recieve an email of the Rhino development team that they will solve this in the next WIP.

Thanks,

Tijl

Attachments:

20110209_loftTroubleoriginalCurves.ghx, 1.4 MB

Permalink Reply by Giulio Piacentino on February 11, 2011 at 7:59am

Yes, there were two things. One intersection bug that was reported and an open question about how to approach this. Nice to hear also the second is solved!
It will be great to hear about the next developments.

- Giulio
___________

giulio@mcneel.com
McNeel Europe, Barcelona

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