Join Veejay Gahir for an in-depth discussion in this video Analyze curve problems, part of Alias Essential Training.
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- One of the most important parts of surfacing is to be able to, obviously, create good quality curves and good quality surfaces, but also to analyze that data effectively. I want to show you how to do that using Curve Analysis. Let's take a look at this basic scenario here. This is not a Class-A surfacing course, so I'm going to touch on the basics of continuity, but we'll leave it at that. I want to show you more of the evaluation functionality. At the very top here, you can see that we have two curves.
Quite obviously, we have a gap between the two. At this point here, we would call this, two curves that don't even meet, G0 continuity. They have a gap. The next two curves that we see down here are G0. What happens here is that the first control point that we see here on this curve and the control point on this curve occupy the same point. As long as they sit on top of each other, we've at least achieved G0, or positional continuity. Now, in this case here, we have a curve on the right-hand side, we have positional continuity because this CV and the CV on this one here occupy the same space.
But we've also got tangency, or G1 continuity, because the combs from both curves lie on exactly the same plane, like this. When they sit on top of each other, we have tangency continuity. Now, the outlines are different. Different values are in different locations, so we haven't achieved G2, but at least in this case, we've achieved G1 or tangency. In this case here, we have again positional, because the two endpoints lie exactly on top of each other.
With tangency condition, this CV, this CV, or those two CVs, and this CV here, all occupy the same line. Remember, those three have to be in the same line to achieve tangency continuity. At the same time, the outside comb, you can see, reaches the same point for both sides. So the value of curvature for this curve and the value of curvature for this curve are exactly the same. Even though there's a peak here, that's fine. That's achieved G2 continuity.
Again that's quite a high level of continuity. In this case here, the last condition, we have G3. Now, with G3, we've achieved positional, we've achieved tangency, combs align right on top of each other, and the outside portion here, in purple, is running through nice and smooth, and that's what we call G3 continuity. Let's go back up to this very top curve here. Let's go ahead and I'll show you how we can achieve this manually. I want to pick this curve, set the pivot point at the end, and then say Move and then snap it to this curve here.
Right now, you can see that we do have tangency. But if I pick this control point here, and I move it vertically, you'll see now the combs are peeling apart. So we've lost tangency there. We still have positional, but we've lost tangency. Now, these combs are located under Locator, Curve Curvature. Let's do a reset. This is how we set those combs up. They're actually locators. If I press l, I will lose all of them. But again, very easy to apply.
Let's go back to Locators, Curve Curvature, and you'll see that we are always using the comb in outline. You can choose just the comb or just the outline. We are selecting Curvature. Not Radius, but Curvature. If I say go to this, I can select this one, this one. Left mouse button increases the amplitude. Middle mouse button increases the density. That gives us a good visual idea of what's happening with these curves. Now, what is the tangency error between these two right now? Well, we can go to Evaluate, Continuity, Curve Continuity, and let's check for tangency.
Let's go Go to that and we can pick that point there, like that. Right now, we are at 8.466 tangency error. If I do control 5, I open up my information window. You can see right now, also, we have 8.46 indicated here. I can go back and change this to Positional. Positional is good. Tangency is narrow, and obviously, curvature is going to be off, as well. Let's see how we can change this to become at least tangent. The first thing to do would be to pick this CV, move it vertically.
Now, as I'm moving it vertically with my right mouse button, I'm going to hold my control right near this point here, and just going to snap it horizontal. I can pick this one at the same time, vertically, hold, and snap like that. Now we are at zero. At this point here, we haven't quite achieved G3, which means that the outside comb would flow over really nice and smoothly. Right now, we've got G2 and we're close to G3. The rule is that we can only now move these control points horizontally. We can go into this mode here, we can say control point, xyz, middle mouse button.
Let's go back into that. I'm actually going to just pick xyz, but I was on proportional modification there. in this case, we're going to go back to the middle mouse button. As you can see now, the combs are still lying on top of each other, so I'm not destroying tangency. But I am changing the curvature value, like so. In order to get them to roll over, I've now adjusted both of them at the same time, like this. What I can do is, I can hold my shift, pick this control point, too. I can also go to the Scale function.
Now, with the Scale function, you'll see that I'm having some really strange results here. Control z. Let's try the middle mouse button. Middle mouse button works way better in this case here. So I'm getting a condition where I'm changing the curvature quite dramatically on the right-hand side. I want to get to a point like this, here. Let's go back to moving just one control point at a time. I'm just moving these out. That's getting very close now to G3 continuity. Now, remember, you can also change other control points to help you get G3.
Let's get close like this. I can actually pick this control point here, and I can actually move this control point. Again, I'm moving it with my left mouse button, but the point here is that you want to try to achieve a kind of roll-over condition. At this point here, we want to be almost flat, as far as the curvature goes. Doing this is what we're looking for. I can achieve that. Then I can middle mouse button to change the height. So that's kind of what I'm looking for now. I can do the same on this side here.
Get close like this, middle mouse button on this one here, and that gets close to G3, like that. Again, this is just a manual way of doing it and getting close. Okay. Let's take a look at some other options with curvature plots. I'm going to go ahead and open up this layer here. Let's zoom into this curve. Let's go into Locators. Let's double-click, and Reset, Go, and this is what we have. Left mouse button, amplitude.
Middle mouse button is density. Okay. Pretty standard stuff. This is a 2D entity. So if I go into my top view like this, you can see that the curvature plot doesn't show anything in this particular view. Let's go back into this view here. What I'm going to do now is, I want to change this into a 3D entity. I want to pick one of these control points, pick CV, jump back into here, and let's say, Move.
I'm going to move with my right mouse button. Now I've started to create more of a 3D entity, like this. Now if I rotate this around, you can see that the curvature plot now is twisting. Now, typically, when you do curvature plots and you're analyzing this kind of data, it's a good idea to try to work in a 2D mode. In other words, try to work in a true view like this. This gives a little bit more of a clear representation of what's happening. Looking at entities in 3D is not always the easiest way to decipher where the problems are. Let's go back to the top view.
I want to pick this CV and I'm going to move this vertically and I want to snap to this NCV here. Let's do the same with this one and snap to the NCV there. Now, I've still got this one selected. I'm just going to move it out just a fraction, like this. Let's go back to this view. Now, there is a different option that we can use here. We can go back in. Let's Delete Locators, open up Curvature Plot, and what I can do now also is, I can add something called Torsion. Let's put on torsion. Let's say Go.
Let's click this, increase the amplitude and density. And if I go into the top view, or I go into a view like this, you'll notice that I have an extra row of combs that appear. Now, this is showing me the twist in the surface as well as the curvature. If I do go ahead and pick one of these control points, say, for example, this one here, and I move like this, you'll notice as the twist in that surface increases, so does that torsion plot. So I do get the option to view twisting, as well.
Let's press l to delete everything. Let's go back into a view like this. Let's pick all the CVs. Let's move vertically, and I'm going to hold alt down and snap them all back down onto the grid like that. Let's go in this view here. Another very useful function in curvature plots is to be able to identify certain radius values. We're always looking at a curvature plot, but we can switch to radius and we can, actually, show radius limits. Let's have a look at this curve.
I want to identify the limits between 100 and 200 millimeters. I'm going to ask Alias to show me where those portions are on this particular curve. Let's pick that curve, again increase the amplitude, left mouse button. My middle mouse button now, I can go ahead and increase the density. By the way, when you're using this command, the denser you make this comb, the more accurate visually you'll be able to see where the imperfections are. This is good for us right now. I've come out of the command.
You can see we have a segment of green here. Now, remember, the analysis was between 100 and 200 millimeters. Let's go ahead and check where exactly that is. Go ahead under Locators, Measure, and we're going to measure the radius. Let's zoom in here. I'm just going to pick on this curve and I'm going to move the locator, like this. I'm going to move just where it starts to turn red like that. I can just hover over that area. You can see that's roughly 200 millimeters. Again, down here, as I move, as I just touch the red portion, it's 100.
So the green area is showing me the area between 100 and 200 millimeters. Now, this can be very useful if you're trying to check a modification, or if you just want to check a specific radius value.
- 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