Creasing a Mesh (part1)

Hi,

I’ve been quite active posting videos, so I now want to catch up writing some posts about the videos and some other interesting topics for any 3D user.

I covered creasing a couple of videos ago, so I’d like to write about it, and dig more into some details for Mesh in general. We already talked about how the fact of having a smooth, continuous surface is achieved by producing an approximation with polygonal faces by adding vertices and subdividing those faces. Continuity is definitely the most interesting characteristic of this scheme.

 

Strange as it may seem, both the cube and the sphere in the image above are topologically the same. The sphere started as a cube that was smoothened into Level 4. The whole structure of the object has not changed after these operations. That’s why we can go back into any level of Smoothness if needed.

Bus as we saw in the example in the video, there are times in which we may need to have certain edges or faces which don’t get smoothed. That’s when we apply Creasing. This command specifies that next to a selected edge, the subdivision needs to be done sharply, by adding steps, which can go from 0.1 into infinity. Actually AutoCAD can use a range from 0.1 to 2 for what we will call variable creasing. The more steps used, the more creased the surface will be. A Crease value 0 means that the object is smooth.

The command MESHCREASE can be found in the Ribbon, with the command MESHUNCREASE, which obviously removes the creasing from a selection. Both commands work either by selecting the geometry and then applying the command, or by selecting geometry after applying the command. Though it may be debatable, I normally use the command after having selected geometry. It may also happen that after the manipulation of a face or edge, we want to crease the selection, and since we already have it done, so it’s just a matter of clicking on the icon or typing the command.

Once MESHCREASE is invoked, we can define its value. The option Always means that we’re applying infinite creasing, meaning, as we said before, that the edges or faces selected are sharp. We can also input any value between 0.1 and 2.

If we need to change the value of any creasing applied, it can be edited through the properties palette, which will display a new category called Crease. Selecting the Type By level, we’ll see a new row called Level appear. That’s where we will input a value for variable creasing.

 

It is important to understand that creasing a Subobject of the Mesh will change the properties of the subdivision, and depending on how we make the model, we may have some challenges when trying to convert into a solid or surface. But it’s all about knowing best practices, so stay tuned for the next post.

Comments

[Mat B]

thanks for the info, very useful blog!
how did you get the layer drop down into your QAT? ive tried and fiddled with all sorts but cant figure it out

[Guillermo Melantoni]

thanks! for the layer drop down, just right click on the layer drop down in the Ribbon, and you'll get an option to put it in the QAT.I'll explain some more tips in a couple of posts.

[Eirik K]

Hi Guillermo.

Thank you for your informative blog.

I have a question:
in architecture terminology and archiCAD (used to work with this) a mesh is often interchangeable with a topographical model. In AutoCAD Architecture 2008 (we had this earlier in our office) we had big problems creating a good topographical model. Now, we switched to 2010, and we thought maybe the Mesh tool would help us to create meshes (topo models). But for now it just seems as if the mesh is a tool to create free form objects, not topography.

Is there a better tool in Autocad 2010 Architecture to create a topographical base for modeling, or is mesh the right place? How would you then go about turning elevated polylines into a mesh?

Would greatly appreciate a little video or a link to tutorial/documentation on the creation of a landscape mesh in ACA 2010.

Cheers,

[Guillermo Melantoni]

Great question, Eirik. There are some potential uses that we can talk about in following posts. Let me prepare an example with some workarounds about this.

[Eirik K]

Thanks Guillermo,

that would be great!

Just to give you an idea of how it works for us, we, as many other architects, often receive a dwg file from our surveyors, sometimes with elevated polylines, sometimes we have to elevated the lines ourselves. But when we use drape for instance in ACA we only get a fairly inaccurate model. We have experienced with creating the mesh in Sketchup and importing it in Autocad, and this sort of works. It is a bit disappointing to us that we don't know how to achieve this in ACA and keep the design and documentation process in one program.

Looking forward to your post : )

Have a great day!

[Matthew Anderson]

Surveyors use Delaunay triangulation to create their surfaces and generate lines of equal elevation, typically shown as contour elevations.