Join Veejay Gahir for an in-depth discussion in this video Symmetrical modeling, part of Alias Essential Training.
- Let's take a look at a very important part of surfacing, and that is symmetrical modeling. So, by symmetrical modeling, we are looking at modeling on one side of the vehicle or a component, and having those changes reflected on the other side of the vehicle at the same time, so there's no danger of having a crease across the center line. So, if we take a look at this example here, I'm going to shade this model up. This model is a concept that I was doing, and it's a very quick concept. At this point here, it's the front hood of an Audi. The way this has been constructed is that this is one surface, but I want to have a nice smooth transition right across the center line.
Let's take a look at the surface itself. You can see that the surface was actually one large surface that's been trimmed back to this particular shape that accomodates the aperture and the opening for the fender. So let's go up to Surface, Trim, Untrim, and we can just go ahead, keep clicking this until we untrim it completely. So again, you can see that this is one slab. During the process of modeling, whenever I change something on one side, I have to have the change reflected on the other side. Otherwise, we're going to have an unbalanced surface.
So there are different techniques to doing this. Some are better than others, but it's down to personal preference and what works best for you. So let's click on the layer single tab, let's hide the trimmed, and let's hide canvas images. Let's go ahead and shade this up. If you don't like the blue color, we can just go to Color here, and let's just pick a gray. Okay, so in this case here, this is the first technique that you can use. Now this one takes a lot of discipline. Essentially we have a surface across the center line, and if we want to change any one of these control points, what we have to do is we have to pick the corresponding point on the other side of the X Z plane.
So, in other words, if I want to change this CV here, I have to pick this CV as well before I go into the Move command. So now if I move like this, both move at the same time. I'm maintaining balance across this center line. If I put on my horizontal vertical zebra stripes, let's window over those two CVs again. Let's say Move, you'll notice that the change is maintaining G3 continuity across there, which is critical in this particular case. Let's go back to regular shading.
If I pick this point here, and I want to move in the X, I have to make sure that I pick this point as well before I make that move. So, this is fine but it does involve a lot of discipline. Where things can go wrong is when you zoom in to an area like this, and you're just fine tuning this area. Let's go into control point movement, we're going to go XYZ control points, and we've got a step size. I've picked this control point and I'm just kind of fine tuning this like that, and I forget to pick this one on the other side. Before you know it, you've got an unbalanced situation.
Another way we can do this is by using just one half of the surface. So let's go ahead and shade this again. So I'm going to pick this surface here and I'm going to just switch on my symmetry. In this case, I'm going to light up the control points on this particular side and now my focus is only on this half of the model. This side here is an instance. So again I can go into Pick CVs, but again if I move this CV, I have to move this one here to maintain tangency across the center line. So, we'll go into the Move command, I can move like this, now I need to adjust this CV here for some reason.
I can go to CVs, pick this one, but I have to pick this one as well. Then go into move. If I don't pick this one, I'm going to lose tangency, and if I put on my zebra stripes here, and I just go to move this one, you can see what happens here with those zebra stripes. If I pick this one at the same time and move, you see at least I'm maintaining the tangency condition there. Again this is fine, but again it involves a little bit of discipline in making sure that you always pick these two control points if you're going to be moving anywhere near that center line.
Now, if we move out toward to this control point here then I don't have an issue because I'm not worried about tangency across the center line. So, again I can put on my zebra stripes. Let's just exaggerate this movement. I can move like this, I can move this one like this, but across the center line, I've got a nice smooth transition. Get a wireframe, and we're going to look at another technique here. This one is called symmetrical modeling. So in this one here, with symmetrical, I want to select the data, let's put on our CV holds.
I'm going to go to Object Edit, Symmetrical Modeling. So with symmetrical modeling, you'll notice that the border goes green, and I have this yellow plane that appears. Now this is the plane of symmetry. So, let's go ahead, pick a CV. I'm going to pick this CV here, but you'll notice the corresponding CV across the X Z plane is selected with a blue marker. Let's select it again, let's go to Move and move up, you'll notice that that one moves accordingly. So now I've built this safety factor where I really can just work with just one CV either in X, Y, or even in the Z direction.
This will always maintain curvature continuity across that center line. So again, let's take a look at this. This is a great way to work, but you do have to have one slab that goes right across the center line. Another way to do this is by using planar line. Now in this case, the benefit of this command is that I'm working with just one half again, I don't have to worry about what's happening on the other side. We've got a bit of an error here as you can see. We don't actually have our border or boundary of the surface sitting exactly on the center line.
Now in this case, I've exaggerated it, this is very obvious to see that. In some case, we could be point one of a millimeter and that's not so easy to see. So in this case, let's select symmetry on, and this is a condition obviously we don't want to have in our modeling process. So how to correct this, we're going to go to Object Edit, Align, Symmetry Plane Align. In this case, the only option that we have is to Project For Position. Now, we're going to leave this on, because if we don't have this on, it will not fix this border here or this boundary.
We want to be able to project this boundary onto the X Z plane. The only way that will happen is if we have Project For Position selected on. Let's say go to that. I'm going to go into the top view, and very simply let's just select this border here. So that's corrected the center line error, and also now we have these blue line markers that's telling us now that we have some sort of symmetry associated to that surface. So let's see how this works. We're going to pick this surface. We're going to put on our CV holds.
Let's go ahead now, pick CV, or we can use our Transform CV tool. Make sure we're in CVs, XYZ, let's take off step size. I'm going to pick this with my right mouse button, move up, and you'll notice now the surface is automatically moving with that movement there. Now if I pick this one here, which is right on the border, it will move this CV. If I move this one, it will pick the one that's on the border, so this is a really great way to model. The focus here is on one half of the hood.
That's a lot better way to model. So, we can just keep continuing on like so. The only thing I don't want to do really is try to move this in the Y direction like that. That's going to break any continuity across there, and that's something that you want to avoid. So let's control Z that, but everything else you can just keep tweaking and the symmetry will be applied accordingly. So this is probably one of the better ways to work, but again, it's all down to preference on which one works better for you, which one you feel more comfortable with while you're doing your modeling.
The main thing to be aware of here is that when you are modeling, and something has to be reflected on the other side, just pay very close attention at certain intervals, just do a check to make sure that everything is symmetrical.
- Manipulating views and entities
- Working with layers
- Creating curves
- Sweeping, extruding, revolving, offsetting, and blending surfaces
- Modifying geometry
- Moving, scaling, flipping, and rotating objects
- Trimming curves and surfaces
- Creating copies of objects
- Aligning, combining, and splitting objects
- Analyzing geometry
- Shading models