One of the most exciting options in the new Mesh modeling commands is the ability to convert a mesh into a solid or a surface. It is really a differentiator, since we can handle different topologies, and have workflows among them.
Once the mesh is converted, it can be manipulated with the Autodesk Shape Manager (ASM), which means that Boolean operations (Union, Subtract, and Intersect) and other operations for solids can be performed.
There are four options for converting to either solid or surface, which are smooth optimized, smooth not optimized, faceted optimized and faceted not optimized. Why so much choice? As a user, do I need to care? In fact, you do, if you want to take advantage of the whole power of this operation.
Let’s start with Convert to Solid.
In order to convert into a solid, we will use the command CONVTOSOLID, or access it from the Ribbon (it is located in the Mesh Modeling tab, in the Convert Mesh panel.
In order to be successful in the conversion into a solid, the object must comply with a couple of conditions. It has to be a watertight structure, which means that there should be no gaps in the model. If there’s a gap, then the operation will not be successful. The example below shows a mesh with a gap. It was done with a revolution, and as you can see, it is not closed. This is the kind of mesh that won't get converted into a solid.
The object can’t self intersect. Self intersections may happen really easily with all the flexibility and power for manipulation that our tools provide. The whole point is that you may not care, if you are going to remain as a mesh. We have already explained how mesh modeling is much more pervasive in the media and entertainment side, and in those cases, fabrication is not an issue. But when we try to create a solid, self intersection is not acceptable.
This is a clear example of self intersecting mesh.
The first option that appears in the right side of the panel will be by default Smooth Optimized. We’ll focus on this option today.
Smooth Optimized will create a smooth solid, and AutoCAD will attempt to stitch faces with G2 continuity. That ensures a solid with the least amount of Nurbs patches. This is especially useful when exporting into Revit. But we’ll leave that for other posts.
I will show a couple of examples that may help understand how much we can optimize the amount of Nurbs patches. It will also help to keep in mind how to proceed when doing mesh modeling. If the final destination is Revit, we will want a low number of patches. If we will remain in AutoCAD, you don’t need to care!
In this first example, I started with a box, increased the smoothness level to 2, and did some manipulation of edges and faces.
When the model is converted into solid, it has 6 patches, which is the least amount of patches that a box can have.
When a crease is applied on the edges of an object like in the example below, you will notice that the solid has one more patch, in order to solve the creasing. Since creasing is basically affecting the continuity, it seems quite obvious that there will be an effect on the way AutoCAD converts into a solid.
Once we convert into solid, it is still worth noting how the conversion still provides a low amount of patches in the rest of the solid.
In the next example, I creased all the faces at the bottom of the box.
This is a pretty obvious case when modeling a building that may normally need to be firmly based on the ground. Something similar happens with the patches in the solid. In the previous examples, more patches were created next to the creasing. The same thing happens here. You’ll notice a second row of patches, simple because of the fact that the creasing affected all the faces at the bottom, thus having an effect over the whole ring of edges.
Another case to take into consideration is when you refine the mesh. If the refinement is done for the complete model, it will behave pretty much in a similar way to the first case.
This is a basic mesh primitive (box) that was refined when in level 2.
The solid created with Smooth Optimized is exactly the same as if we had used the primitive in Level 2 with no refinement.
AutoCAD can really make a good optimization of the faces in the mesh. You can see this in the example below.
In this case, we'll refine the box and make some manipulaitons that add more complexity to the overall shape.
After refining and manipulating faces, we still have 6 patches!
However, if we refine a specific part of the model, the optimization will be less predictable. Refining selection is in my opinion a very interesting way for working with less faces, and only adding complexity where needed. As I said before, you may or may not care about the amount of Nurbs patches in the object.
This is the mesh with a couple of faces refined.
The resulting solid has much more patches.
There’s a lot more to cover, but we’ll keep it simple now, and elaborate in following postings.