Join Veejay Gahir for an in-depth discussion in this video Evaluating curve continuity, part of Alias Essential Training.
- Let's take a look at how to evaluate curve continuity. So we looked at surface continuity and curve continuity is just as important. Typically when we're doing a surfacing exercise, we'll start with curves, so if we can make the continuity really good between those curves, the resulting surfaces will inherit that quality level and should be a lot better. So let's take a look at these two curves here to start with. So we're going to do an Evaluation function here, so Continuity, Curve Continuity and we're going to say Reset with that and let's just go with Position for now.
So I'm going to pick right at the common point between those two curves and I end up with a little green square. Now that's telling me that that is positional continuity or G0. Now, I've got my Information Window opened up as well. Because that locator is selected, I can get information about that. If it's not selected, just go up to Pick, Locators, pick that locator and go back into Information Window. So the Information Window is great because it tells you that you're on Position continuity and if I want to now change to Tangency I can simply go Tangency from here.
So now it's telling me that we have a .083 tangency error between those two curves. It's not always a good solution to just go ahead and apply an align to fix this because sometimes, we want to be in more control and a little bit more discreet about how we fix this error. So this is a tangency error, so what we have to do now is we need to modify one of these control points so that we have all three lined up in a straight line. So for the moment, I want to delete this and let's take a look at this error here.
Ideally we need to have a straight line so let's go ahead and just put a line in like this. And I'm going to switch off the control points and let's move our Control Panel down like this and I'm going to go into a View Twist mode. And then let's go ahead and exaggerate the vertical axis like this, and this is where this function starts to be really important. And you can see here, that we do in fact have a slight kink in those two control points. So, there's the straight line and that's exactly where we need to be.
So either we can move those two points down or we can move one of these points up until they're all in a straight line. Let's go ahead and let's delete this. Let's press this option here to bring it back to 1 to 1 scale and we're going to go left. So let's go back to Continuity, Curve Continuity, let's pick that. Information box let's change to Tangency. And let's take a look at how we can fix this. So we're going to use control point manipulation, so let's go to our Transform CV tool. I'm going to move CVs XYZ, and we're going to turn the mouse sensitivity right up like this, because we are going to be moving very very small movements here.
If we don't, it's going to be a little bit too erratic. And just simply with my right mouse button, I'm going to move this point up like this, until that marker goes green like so. So as soon as it drops below .05, it's green, so we've met tangency here. I could continue on until I get to an absolute value of 0. Let's take a look at what value, or how that's set, so we can go into our Preferences, let's go to Construction Options and we're in Inventor and under Tolerances, Continuity, Tangency or Continuity Angle, has to be less than or equal to .05 millimeters.
And sure enough, we ended up just below 05 and now we're at 009. So again, I could go ahead, I could keep moving this, or if I really want to get to a value of zero, I can turn the mouse sensitivity right up to maximum because we are really going to be moving very very small increments here and I'm going to go down to, there we are, zero. So let's go back to our information and we're going to back, pick our Locator. Pick the locator like that, Information Window and let's go to Curvature now.
So the curvature value is 016, so we change this as well. We use the same principle but this time, I'm going to have to move in a tangent vector. If I move this up, I want to break tangency. So let's pick this CV over here and I'm going to go back and change the mouse sensitivity back to something like, somewhere in mid way like that. Maybe a little bit more would work. So what we need to do here is look at where it starts to go green, and at this point here, I'm going to change my mouse sensitivity like this, and now I can do some real fine movements and there we go.
So under .05, we have G2 continuity. Now again, I could carry on doing this if I wanted it to achieve zero but this would meet all the criteria for Inventor if we send this data through. Now, as well as taking a look at curve data, we can also analyze curves on a surface. So I'm going to move over to a different layer now. And let's just make this one invisible. So what we want to do now is we want to analyze the way, let's say, these two fillet edges are running into each other.
So we don't have curves here right now, we can do an Evaluation, we can do Surface Continuity, we can do Tangency, just pick this edge here like that and you'll see that we get an internal tangency reading. And also, this is telling us that the ends are tangent but I want to specifically look at those curves. So the way to do this would be to extract those curves, so I could go to Curve Edit, Duplicate and I could pick this piece of data here, spacebar to accept, this piece of data here, this one, spacebar, and spacebar again.
So let's do this now, let's go Pick, Components, everything Off, pick only the Curves, let's say Go, and then hide everything else. So what we have now, if I switch off the CV/Hulls, actually let's go ahead and switch off the Edit Points as well. So we have two distinct entities, we have one here and one there. What we can do now is just measure the tangency between those two curves. Actually, I'm going to just put on Edit Points on one of those curves like that so I can see where the common point is.
So again, let's go to Curve Continuity, we're going to go to Position, let's select this one and we can go up and change this to Tangency. So right now, it's telling us that Tangency is at 0.055 so it's just a fraction out, in that case. So in this one here, we can also change this one to Tangency. So in this one here, we're fine at 0.002 but this one here we're at 0.055. Now ultimately, we would check the surfaces so if I bring all the surfaces back, the real test will be checking the evaluation values for the surface rather than extracting curves and then checking the curves.
When we extract a curve from a surface, we are actually creating a re-approximation of that edge. So if you do need to do that, just rebuild those edges and then do an evaluation, as I've shown you.
- 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