topic Re: Combining Surfaces in AutoCAD Forum

Combining Surfaces

Anonymous — Fri, 14 Jul 2017 21:06:08 GMT

Hello,

I have a solid terrain created by contours. The top surface of solid is collection +500 small surfaces. I do need to combine all top surfaces and make them as one surface to be able to create a mesh in another pre-processor for meshing procedure. Can anyone help me out please?. The file is attached in case you wanna look at it. Thank you.

Regards,

Muhsin

Re: Combining Surfaces

Alfred.NESWADBA — Sat, 15 Jul 2017 08:19:41 GMT

Hi,

one possible workflow:

delete the 3D-Faces, so only the 3D-Solid remains.
you can now use command _CONVTOSURFACE

another option is command _CONVTOSURFACE, but that creates many objects (area-by-area) which then need to be joined using command _UNION.

HTH, - alfred -

Re: Combining Surfaces

SEANT61 — Sat, 15 Jul 2017 08:34:04 GMT

This may or may not help. The solid was sliced via lofted surface, and may not work well with downstream processing either.

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 15:39:36 GMT

Dear @Alfred.NESWADBA,

I have converted the solid to surfaces using _CONVTOSURFACE. Because the top surface of solid had many small surfaces, I exploded top surface and tried combine them. Unfortunately, I failed. How can I union the exploded surfaces ? the file is attached.Thank you.

Muhsin

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 16:01:02 GMT

Hi,

>> Unfortunately, I failed

Which message did you receive from AutoCAD, by default it shows you one or more reasons about what happened.

- alfred -

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 16:19:26 GMT

I was using Union function, assuming it may work for surfaces. It took around 10 min to recover itself. but nothing happened to top surfaces.

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 16:28:11 GMT

Hi,

>> I was using Union function, assuming it may work for surfaces

Yep, it works for surfaces, but not for (none coplanar) region objects. And your second drawing only contains regions, no surfaces.

So I guess _EXPLODE is not an options.

And I'm quite sure you have got a message back from AutoCAD:

- alfred -

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 16:33:42 GMT

Yes, I had that warning in the prompt. So, I have no idea how to merge those surfaces. What would u suggest me in that case ?

Thank you.

Muhsin

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 16:45:41 GMT

Hi,

>> What would u suggest me in that case ?

At least not using _EXPLODE.

Or when you want to start with the region objects you can use command _MESHOPTIONS to convert the regions to meshes, then run command _UNION and convert the meshes to surfaces.

But it's hard to say what would be the best for your workflow as I don't know your goal (and have not understood it from the other thread where I created that solid).

- alfred -

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 16:54:18 GMT

Hi,

please find attached the result of the alternative workflow mentioned in my previous post.

- alfred -

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 18:10:27 GMT

Dear @Alfred.NESWADBA,

My goal is to having a solid that has one single surface at the top and 5 at the sides and bottom. I am going to transfer that solid to FEM software. In this case I cannot work with this solid because small small surfaces causes problem with meshing process in FEM software. Sorry for misunderstanding. Unfortunately, The surface you created in the last attach is still having small surfaces at the top. Thank you

Muhsin

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 18:19:03 GMT

Hi,

>> My goal is to having a solid that has one single surface at the top and 5 at the sides and bottom.

Well, your first drawing in your post has such a 3D-Solid.

>> In this case I cannot work with this solid because small small surfaces causes problem

>> with meshing process in FEM software

So you need to reduce the quality from the triangulated 3D-Solid ... but this triangulation was based on your contour lines.

So the way to go is back to Civil 3D, create a surface based on your contour lines, then reduce the quality (which tolerances are given for that process?)

After that recreate the 3D-Solid from the Civil 3D surface.

- alfred -

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 18:27:13 GMT

I need that topography to place the structure on. I have used 80x80 spacing for the current file to from the surface. Wouldn't reducing the quality give the collection of triangular surfaces again? Thank you.

Muhsin

Re: Combining Surfaces

Alfred.NESWADBA — Sun, 16 Jul 2017 18:36:38 GMT

Hi,

>> Wouldn't reducing the quality give the collection of triangular surfaces again?

Working with Civil 3D always generates surfaces based on triangles.

Does your FEM-software only work with rectangle based faces?

Is the limitation the size of the triangles or the number of the triangles?

At least reducing the number of geometry will reduce the quality (as long as you don't have neighbored faces with the same slope ... they can be combined to one face without losing quality)

- alfred -

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 19:02:54 GMT

I am going to try to reduce the quality. But can you please tell me how I do combine the top surfaces to one surface? That's the killing part I guess. Thanks

Muhsin

Re: Combining Surfaces

SEANT61 — Sun, 16 Jul 2017 19:07:58 GMT

What happens when you try to use the solid that I attached in Post #3 of this thread?

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 19:15:17 GMT

Deat @SEANT61;

I am so sorry I just realised you have attached a file to this thread. I looked at it now and I could successfully transfer the solid to FEM software with single a single top surface. I appreciate it. Can you please explain a little bit more what you have done to the solid ? Thank you.

Muhsin

Re: Combining Surfaces

SEANT61 — Sun, 16 Jul 2017 19:28:12 GMT

I’m working on an AutoCAD add-in that processes contours at elevation into a rectangular lofted surface. I used that surface to Slice a solid to produce the solid you see in that file.

Re: Combining Surfaces

Anonymous — Sun, 16 Jul 2017 19:50:29 GMT

Dear @SEANT61,

I am sorry but I am having difficulty to understand what you have done. It might because I am not a native speaker. Can you please rephrase the steps you have done? I spent lots of time to solve this problem but couldn't. Thank you.

Muhsin

Re: Combining Surfaces

SEANT61 — Sun, 16 Jul 2017 20:18:17 GMT

Similar to the process that creates a surface with Civil 3D, I'm using a command that is not native to AutoCAD. The command analyzes contours and recreates the surface via a rectangular lofted surface. The attached is the intermediate step, before using the surface to slice a solid as I did in my first attachment.