Welding Vertices in MAX 4

Polygonal modeling is basic, and the serious modeler understands his or her polygonal modeling toolset completely. This current series of lessons represents nothing other than my own very careful attempt to clarify for myself the ways in which the new generation Editable Poly object differs from the traditional Editable Mesh. It's smarter to obtain this understanding with simple tests, than by winging it in a real modeling project with all of its practical complications. I like to understand my tools, at least in a fundamental way, before I being a serious task.

Thus far, the Editable Poly has proven more flexible and easier to use than Editable Mesh in every respect. Let's focus on a contrast between the two that is a bit more confusing.

Once again, we see an Editable Mesh cube (in pink) on the left and an Editable Poly version (in green) on the right.

Welding vertices is a basic operation in all polygonal modeling applications. The traditional approach in Editable Mesh is easy to use and commonly practiced. In the Vertex sub-object mode, you have two welding choices - Selected and Target.

To use the Selected approach, you first select all the vertices you want to weld into a single vertex. Then you press the Selected button to weld them. All vertices that are within a threshold distance of each other are welded. You often have to adjust the distance spinner next to the button to make sure that you've set an adequate distance.

Here's the Editable Mesh with two vertices selected.

After setting a distance spinner to a value large enough to include the distance between these vertices, I press the Selected button. The edge between the two vertices disappears, and the two vertices merge into one at the midpoint between their original distances.

This looks simple enough, but let's examine things a bit more carefully because, after all, this is MAX. If we switch to Edge sub-object mode, we see peculiar dotted edges. What's that all about?

As it turns out, the welding process created duplicate edges. Instead of four edges meeting at the welded vertex, there are eight. Each apparent edge is actually two edges on top of each other, as you can confirm by selecting and checking the display in the Editable Mesh panel. In fact, the situation is even worse than that, because an invisible diagonal edge has also been doubled. Try this out yourself to make sure you understand the issue.

What does this mean in practical terms? In my experience, this duplicate edge problem can sometimes cause bizarre peculiarities when editing a mesh, and that seem to defy understanding. In any case, it's confusing. For the moment, just be aware of the issue. As welding is so essential, you just have to put up with the consequences.

Target welding involves dragging from one vertex to another. The vertex that you drag from is welded to the second vertex, right on the location of the second vertex. This technique can be a little confusing to those who are not used to it. You must first activate the Target button to get into the Target weld mode. With the Target button on, click on a vertex to select it. The Transform Gizmo will appear with its axis tripod, but don't be misled by this.

Drag across the screen until you are on top your target vertex. The vertex will not follow, but a little cross icon will appear when you reach the target vertex. Release the mouse button to perform the weld. Be sure to click on the Target button to get out of the Target weld mode.

If you now jump to the Edge sub-object mode, you'll find duplicate edge problems, similar to what we saw before. In fact, if you collapse an edge, rather than weld its two vertices, you'll also find duplicate edges in Editable Mesh. There seems to be no way around it.

With this background, let's consider the welding in the new Editable Poly object.

The Vertex sub-object panel of Editable Poly contains precisely the same welding options as its brother in Editable Mesh. But if you try to use the Selected option to weld two vertices on a cube, you get a rather peculiar message.

Any reasonable person would think this means that the threshold distance hasn't been set high enough. But you can set the distance as high as you want and still get this message. The real point of the message is that there are no weldable vertices selected.

As it turns out, you can't use the Selected weld option on an Editable Poly object at all, with one important exception that we'll get to shortly. The only alternative is to select the edges between the vertices you want to weld and collapse them. But there's a good side to this. This approach doesn't produce any of the peculiar duplicate edges that we find in Editable Mesh.

What about Target welding? Give this a try on an Editable Poly cube and notice that activating the Target weld mode has no effect. You can't select any vertices, and you don't even get any error messages. In this case, there's no alternative. You're simply out of luck.

So why are these welding options on the Editable Poly panel at all? They survive in a limited, but important, way. The Editable Poly object offers a new sub-object mode called Border. I'm afraid I haven't yet come to fully understand it's value, but the idea is that one can select all the edges that define an opening in a polygonal mesh. For example, if we select the top quad on our Editable Poly cube and delete it, the top four edges can be selected as a single border.

This concept of a border is somehow fundamental to the internal representation of an Editable Poly object because vertex welding is possible only on vertices surrounding an open region of mesh. And even this is much less than one would expect. For example, you can't seem to weld two adjacent vertices around a border, regardless of whether you use the Target or Selected method. On the other hand, you can perform other welds that would destroy the mesh.

The real value of this exception for border vertices is the ability to weld together two separate mesh elements to create a single contiguous piece of mesh. This might take place when stitching a new unit onto a larger mesh (like a hand to the end of an arm), but is most common when merging the two mirrored halves of an object (like a character figure) that was modeled only on one side.

Editable Poly is as new to me as it is to all MAX users, but I'm satisfied that this is the direction to go. Older MAX users like myself need time to adjust to new toolsets, but newer users should jump right in with Editable Poly. The greater flexibility and ease-of-use in Editable Poly is important, to be sure. But I'm even more hopeful that this new kind of object will be more reliable than Editable Mesh. Editable Mesh (and Edit Mesh) modeling has long been plagued with indefensible bugs (like the constant and mysterious generation of duplicate vertices requiring welding). Although it's too early to say, it's possible that working with Editable Poly will require less tedious vigilance and will be much easier for newcomers to learn.

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