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  Tutorials 3D Graphics Tutorials Polygon Modeling: Techiques I

Polygon Modeling: Techiques I

Onno van Braam Tutorials Jun 15, 2006

Summary

Okay, now that we have covered most of the available tools in each sub-object, it is time to apply them. Yet we will not apply them to a specific modeling problem just yet, such as modeling a wheel rim. Why not? Because it's time to understand the interaction between your Editable Poly and MeshSmooth. This interaction can be be delicate at times and at other times it works completely logical.

The Essentials and 2 Examples

When you're modeling and you apply meshsmooth to a model you will have noticed that not your entire mesh gets evenly smoothed (and not because of vertex weights, we will not use them). This is always because of your mesh density: your mesh density, as I call it, is the all important thing when polymodeling in combination with MeshSmooth. So what is the mesh density? Well your model could look exactly the same as mine before MeshSmooting, but afterwards it could look totally different.

Example 1: Suppose we have a cube (100x100x100 in size), on the left it has 1 segment in each dimension, in the middle three and on the right it has ten. As anyone can see, and which is pretty obvious they all have exactly the same shape... they're cubes, so duh! But then I apply a meshsmooth (MS from now on) with one iteration, the result is shown below each cube.

image 1

THIS IS IT, this is what poly modeling is all about. Try to understand what is happening here. The result is very very clear: the cube with 1x1x1 segments is extremely smoothed (it has almost become a sphere), the second cube is way less smoothed but then again, the cube with 10x10x10 segments is still very similar to it's original shape.

The denser your mesh before MS'ing, the less smoothed it becomes.

That's the rule and that is what you will think of all the time when you're poly-modeling. Every action you perform, you think: hm, what will happen when I MS? Or even better, know beforehand, and therefor you will think: I do this and this, because when I MS, this will not get smoothed since I made the mesh dense.

Let's redo the example above, only in a slightly different way.

Example 2: We make the second cube again (100x100x100, with 3x3x3 segments). Only this time we will want to create the same end result, so after MS'ing as on the cube with 10x10x10 segments. As you will understand it is a lot more efficient if we could do that (MS'ing quadruples your polycount on each iteration). So create it, convert it to an EP, then go to the VSO and move the middle two rows of vertices closer to the edge (I selected and scaled them 275% from different viewports, it doesn't matter how you do it, as long as you get it done).

image 2
Click to enlarge

So I move all the vertices towards the edges (literally) of the cube, since what I want is a cube with sharp edges, I don't want a blobby cube, I want a well defined cube only then with nice smoothed edges. I did it in three steps as you can see on the images, below the 4 is the end result (with and without meshsmooth), a bit zoomed in. You can see clearly that the shape hasn't changed at all, it's exactly the same as before. The only thing we did was move some vertices around to densify our mesh at the places where we want them, which is exactly the whole idea behind polymodeling. On the final right bottom image the result is shown: a very cube like shape, only with nice semi-smooth edges. It's a step in the right direction. Moving vertices around to densify your mesh in desired places is a valid way of getting what you want out of MS. Yet it means that the vertices that you move away from where they were didn't define a shape you wanted... otherwise you would loose the shape of your model, but gained definition at other places. There must be other ways to get where we just got.

Chamfering

There is indeed: it's called chamfering. As explained in the previous tutorials, and especially the one about the ESO, I mentioned chamfering and how important it would become later on. Well here goes.

Example 3: Create a new cube, 100x100x100 in size with 1x1x1 segments, convert it to an EP, go to the edge sub-object. Okay we are going to get the same result as before, but this time we create the smooth edges by chamfering, so you get smooth edges and a denser mesh at the borders which will in return result in what you want when MS'ing. Select all edges, click 'Chamfer' (the little window next to it), set Chamfer Amount to 1.0 (default) and click Ok (not Apply). Congratulations, you have chamfered and therefore your are! ;) Apply a MS with 2 iterations. We use more iterations because our mesh is so empty before MS'ing that it gets very little definition would we use 1 iteration (try and see what I mean). Okay, so our goal is accomplished, but there is still some things to explain.

Do the same as before only set the Chamfering Amount to 5. Both steps and results can be seen in the next image, and work both as we expected: set the Chamfer Amount smaller and the end result are very sharp borders / edges, set the Chamfer Amount larger and the end result is smoother. So the denser your mesh, the sharper the end result.

image 3
Click to enlarge

This about wraps it up, concerning the chamfering and densifying your mesh. Try to understand what I am getting at, since it's the core of poly/MeshSmooth modeling. Hereafter I will explain some of the techniques I have learned over the years.

Making holes

This won't be an explanation of theory, but more an application, or serie of events to create nice round holes in an object. The end result isn't very tidy (in that you are left with some garbage vertices, but it gives a good idea of how to do something).

So create a new box, 100x100x100 with 1x1x1 segments, convert to EP, go to the PSO. Select a side polygon (1), click 'Tessellate' twice (2) (this as mentioned in Tutorial 4 slices your polies). Then select the middle 4 polygons (3) and click collapse (4). Now you have a sort of star like polygon configuration where your original polygon used to be.

image 4
Click to enlarge

Go to the VSO, select the middle vertex of the 'star' (1) and chamfer it (to the size you want) so that you create a new centered circular shaped polygon (2). Go to the PSO, select the new center polygon (3) and extrude it inwards (4).

image 5
Click to enlarge

That's it, but we want it to look good when MS'ing! So go to the ESO, select on the edges (1) of your hole and another one on the inside (2), and then press 'Loop' (3). Hopefully it selects the two 'rings' of edges, in my case it didn't so I had to select them by hand. Then I chamfered the edges by an amount of 1.0 (4).

image 6
Click to enlarge

Then to make the whole cube not become very blobby and smooth when MS'ing, I also chamfer the other edges (1) by an amount of 3.0 (2), since I want them to be defined but not as much as the hole edges. Then I apply a MS with 2 iterations (3).

image 7

If you want the hole go from one side to the other, then do the exact same procedure on the other side of the cube, but delete the two center polygons and connect the two newly created cubes by welding the vertices.

Another way of doing it: select the whole side and hole (1), for instance by using grow after selecting the center polygon, then shift-rotate it 180 degrees (hold shift and then rotate your selection which will in effect copy it, press a beforehand to rotate with steps of 5 degrees), clone to element and move it a bit away (2), deselect it. Then rotate your view and delete the side polygon after selecting it (3 + 4)

image 8
Click to enlarge

Then turn on snap (s) and set it (by right clicking it) that it snaps to vertices. Select one of the polygons of the copied hole (1), start clicking grow like a madman until the whole hole is selected (2), then move it (by using snap) towards the place where you just deleted the polygon (3).

image 9
Click to enlarge

Deselect all, go to the VSO, select all, and then press 'Weld' (the vertex count should be 4 less after the welding), apply the MS again and lo and behold the result. It probably doesn't work very well, since the original side is still different from the original one, this is because the chamfering was done after the collapsing.So the best way would be to just copy the entire side, including edges (1), delete the whole other side and do the same as explained before (2). More vertices should weld and the result should be better (3).

Polygon Modeling: Techiques I

The last part went a bit quickly and sloppy, but it's just to explain certain handy procedures.

This about wraps it up for this tutorial, more in Polygon Modeling: Techiques II.

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