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You are here: Homepage /  Tutorials & Tips /  Tutorials / Polygon Modeling 6: Techniques II
 Polygon Modeling 6: Techniques II
Posted: Jun 04, 2007
Homepage: none
Software: Autodesk 3ds Max
Category: Modeling
Skill: Intermediate
 Tutorial Steps 1Summary 2Creases 3Problem 2: Crossing Creases II 4Problem 3: Creases / chamfered edges on bend surfaces

Summary

More techniques and procedures will be explained in this tutorial. And also problems you could encounter when applying the explained techniques.

Creases

Everybody wants to know about creases, especially when car modeling they're essential for a nice result. Very often you see those blobby creases which make a car look very undefined and ugly. In the next section I will try and explain way(s) of making them.

The steps will be:

Edge: Chamfer

Poly: Extrude

Edge: Chamfer

Once again create a box, 100x100x100 in size and 1x1x1 segments, convert to EP. Go to the PSO and select all polygons (1), from a side viewport slice your box in half (2) using Slice Plane (3), go to the ESO, select the newly created edges (4) (or they should already be in fact) and chamfer them with an amount of 3.0 (5).

You can see the crease approaching! ;) Back to the PSO, select the newly created polygons (1), extrude inwards (2) (By Group, height -5.0). Then when you go back to the ESO, you should notice that the edges are still selected (3) (exactly the ones we want), chamfer them by an amount of 1.0 (4). Then if you want the cube to remain cubish (this is not necessary, but we'll do it anyway) select (5) and chamfer (6) the other edges with an amount of 2.0.

The important and essential steps are of course: chamfer edge, extrude inwards, chamfer edge, as described beforehand. If you want you could also chamfer the edges on the inside of the extrusion part. Anyways, apply a MS with iterations 2 and your result should match the next image:

That is it, there is nothing more to it: chamfer, extrude, chamfer. Remember that, apply it and it always works. At least is has for me in the last years.

Problems

Off course it's not always as straightforward and easy as with this cube. In fact it hardly ever is... And then it may well be that you (and me too) will run into problems. These problems could be (an explanation of how to deal with them follows below):

1. You could have created a crease one way and then want another crease and that crosses the original one. This problem is best to be avoided.

2. Creating crossing creases (the 1st one is almost the same, but this one is still different).

3. Creases / chamfered edges on bend surfaces: one of the mother of all problems when polymodeling.

Problem 1: Crossing creases I

Suppose you have made a couple of creases on your model (like I did on the image below) and want to make an additional crease along the red line. It looks trivial, but unfortunately it's not. The second part of the creasing process, the poly extrude will not work as expected.

I will have a go at it, so I select the edges (1) (by using 'Loop'), chamfer (2), since that shouldn't be any problem. And then select (3) the polies that need to be extruded inwards.

Here lies the problem... we can't just go and extrude! Since then the part where there already is a crease will be extruded inwards for the second time. There's a way to extrude anyways now, but it's very, very cumbersome and hard work. It would encompass extruding parts, then deletion of existing polygons, creating new ones and hoping it all matches up. As follows: deselect the already creased part (2), extrude inwards (3), select polies that are in the way (4), delete them (5), create new polies to fill up the gaps (6 + 7 + 8). It works, but then you also have to make the chamfering of the edges match. And believe me all this is very very tedious work.

So there's a solution, but is there others? Yes, yes there is. It's a trivial one: create all your creases that cross at the same time! This will save you so incredibly much time. As you can see in my Porsche WIP progress from image 2 to 3 I created all creases in one big sweep. It was one 'chamfer' command, one extrude and one chamfer again, because they were almost all linked together somehow it had to be done all at once.

Problem 2: Crossing Creases II

It's very easy to think that this is not a problem. But I will show you it is! ;) You don't have to do this yourself, looking at my images and reading what I do will be enough to see what's going on.

I create a box, 100x100x100 with 2x2x2 segments (1), and create the crossing creases (select (2), chamfer (3), extrude (4), chamfer (5) and MS with 2 iterations (6)) exactly the way I did in the previous example, only now with some more edges to which I apply the chamfer, extrude, chamfer trick.

As you can see, where the creases cross each other a big tearing / hole appears. Not what you could possibly want. The question of course is, before we can solve it: why is this happening? It is happening because densifying you mesh when chamfering has a direction and MS has too. MS tends to smooth negatively perpendicular to the average of normals of the surfaces. So if you would take the normals of two faces, averaged them, and then inverse it (make it negative), then you get the direction MS would work in. Sounds a bit complicated, but it's a feeling you will get along the way of learning how to model. In the next image I tried to explain by drawing some images, how the direction would be.

Now that we know the cause of the problem, we can go and do something about it. Naturally our mesh densifying by chamfering comes to the rescue. Select the four standing edges, see image below, and chamfer them, so that they create a sort of barrier for the MS.

Hooray! That'll teach 'em! We win, we will always win. :D Modelers: 1, MeshSmooth: 0. Anyways, when MS doesn't do what you want, like it did just now, then densify your mesh in the places you think the cause of the problem lies and see whether it gives the desired result. If not then try other places to densify, densifying is always the solution. Always.

Problem 3: Creases / chamfered edges on bend surfaces

This is a problem that is hard to avoid and also quite hard to defeat. In short it's a problem that you want to densify your mesh somewhere, and it does what you want, but as a side effect it has effect on your model when you MS which you don't want.

I will use a tube in this example, which is curved and not flat as the cube was, converted to an EP and some extra segments. I'll first chamfer the edges of the side by selecting two edges (2) and then Loop (3), chamfer (4) and MS with 2 iterations (5). All expected behaviour: one side with nice edges, other side very blobby.

All is well, yet now the problem: what if I want a rectangular inset in the side? I'll do it and the problems will occur automagically.

So I selected the polygons I wanted to extrude inwards (1), extruded them inwards (2), selected the edges (3) and also the edges on the inside (4)(including the standing ones in the corner!), chamfered them (5) and then applies MS with 2 iterations.

Looks good, but in fact it's fairly hopeless. From this angle it's hard to see the problem, but let me rotate the camera for you. See this side view:

It's not circular anymore see the right part of the previous image, there's a bulge right now. It seems minor, but believe me this is something that you see when you use reflective materials such as a car paint or chrome. Also realize that this problem will always occur when you have a curved surface and you start extruding inwards and chamfer some edges. It's a problem you'll be facing non-stop if you're working with cars. There's almost no car where there's no things that go inside on the car body and those are the places where it goes wrong. With NURBS this would be a piece of cake, but we're modeling indirectly, so it may look like it's going okay but the only thing that counts is after you have applied meshsmooth.

And now for the solution: the solution isn't one way. There's no default solution. The only general plan of work is to make your mesh denser around the problem area and form it the way it would look after you had applies MS. This way you 'fool' MS: it's dense so MS doesn't have much influence, and it has the right shape so it will remain good. Let's have a go at it.

I sliced a couple of times and moved the vertices around (with a Circle as guidance to see whether it matched up with it) while using the 'Show end Result' button in the modifier roll-out to instantly see the result of moving the vertices and slicing. It takes a bit of feeling (which is hard to explain in this tutorial) but just slice a bit to dense it up, and then reshape it so that is matches the shape you want again. So once more the densifying is the solution.

As said, there's very little that you cannot solve by making your mesh denser. And that is no surprise, since what you de facto do is play to be MS, you are actually smoothing things out. So try to make your mesh as undense as possible and let MS do the work, yet if that doesn't give the wanted result, then you densify it at place where it fucks up. If that gives wrong result again, try to tweak it and fool MS.

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